Browsing by Author "Melis, Robertus Johannes Maria."

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A study of bruchid resistance and its inheritance in Malawian dry bean germplasm.
(2007) Kananji, Geoffrey Acrey Duncan.; Melis, Robertus Johannes Maria.; Derera, John.; Laing, Mark Delmege.
Dry bean (Phaseolus vulgaris L.) is economically and nutritionally an important legume, not only in Malawi, but in many parts of Africa and Latin America. Unfortunately, two bruchid species (Acanthoscelides obtectus Say, and Zabrotes subfasciatus Boheman) are known to cause extensive damage in storage, reducing the economic importance, food value and planting value of the crop. The aim of this study was to: i) ascertain farmers’ perceptions of the importance of bruchids as storage pests, and to identify their preferred varietal traits in dry beans; ii) screen Malawian dry bean landraces for effective and adaptable sources of resistance to the two bruchid species; iii) determine the gene action and inheritance of bruchid resistance. Farmers’ perceptions on the importance of the two bruchid species to beans both in the field and in storage were established using a participatory rural appraisal (PRA) in three extension planning areas (EPAs) in Lilongwe agricultural development division (ADD). Results confirmed that the two bruchid species are important storage pests, causing serious storage losses among smallholder farmers. In the absence of any control measures, farmers indicated that more than 50% of their stored beans could be lost to bruchids. Indigenous bruchid control measures are not very effective, making it necessary to search for other control methods. It was also clear from the PRA results that breeders need to consider both agronomic and culinary traits in bean cultivar development. This would enhance uptake of newly developed varieties. To address the problem of bruchid damage experienced by smallholder farmers, a total of 135 dry bean genotypes, comprising 77 landraces and 58 improved varieties (obtained from collaborating partners) were tested under laboratory infestation (nochoice test methods) and field infestation (free-choice test methods). The objective of this study was to identify effective sources of resistance to the two bruchid species. Results of the study showed that there was a wide variation among the genotypes for resistance to the two bruchid species. Overall results showed that 88% of the genotypes ranged from susceptible to highly susceptible to Z. subfasciatus and only 12% of the genotypes were moderately resistant to resistant. Genotype screening for resistance to A. obtectus showed that only 12.5% were resistant, whereas 87.5% were moderately to highly susceptible. All of the improved genotypes were 100% susceptible to A. obtectus in storage. One landrace, KK35, consistently showed a high level of resistance to both bruchids under laboratory infestation, with results similar to the resistant checks (SMARC 2 and SMARC 4), while another landrace, KK90, displayed stable resistance under both laboratory and field infestation. However, performance of most genotypes was not consistent with field and laboratory screenings, suggesting that mechanisms of bruchid resistance in the field are different from that in the laboratory and field screening should always be used to validate laboratory screening. Resistance in the field was not influenced by morphological traits. The seed coat played a significant role in conferring resistance to both bruchid species in the laboratory, whereas arcelin did not play any significant role in conferring resistance in the landraces. The inheritance of resistance to A. obtectus was studied in a 6 x 6 complete diallel mating design, involving crosses of selected Malawian dry bean landraces. The F1 crosses, their reciprocals, and six parents were infested with seven F1 generation (1 to 3 d old) insects of A. obtectus in a laboratory, no-choice test. There were significant differences among genotypes for general combining ability (GCA) and specific combining ability (SCA). However, SCA accounted for 81% of the sum of squares for the crosses, indicating predominance of the non-additive gene action contributing to bruchid resistance. A chi-square test for a single gene model showed that 5 of the 13 F2 populations fitted the 1:2:1 segregation ratio of resistant, intermediate and susceptible classes, respectively indicating partial dominance. The eight F2 populations did not conform to the two gene model of 1:4:6:4:1 segregation ratio of resistant, moderately resistant, moderately susceptible, susceptible and highly susceptible classes, respectively. Average degree of dominance was in the partial dominance range in five F3 populations, but in general resistance was controlled by over-dominance gene action in the F2 populations. The additive-dominance model was adequate to explain the variation among genotypes indicating that epistatic effects were not important in controlling the bruchid resistance. The frequency distribution of the 13 F3 populations for resistance to A. obtectus provided evidence for transgressive segregation, suggesting that resistance is conditioned by more than one gene. Reciprocal differences were not significant in the F2 generation seed; but were significant in four crosses in the F3 generation seed for adult bruchid emergence, suggesting that maternal effects or cytoplasmic gene effects also played a role in the inheritance of resistance to the common bean weevil. Through this study, important sources of bruchid resistance in dry bean have been identified in Malawian landraces (KK35, KK90 and KK73). These resistant sources will be used in a breeding programme to develop bruchid resistant bean cultivars, as well as improve resistance in susceptible commercial bean cultivars currently grown by farmers in Malawi.
Breeding and evaluation of cassava for high storage root yield and early bulking in Uganda.
(2013) Tumuhimbise, Robooni.; Melis, Robertus Johannes Maria.; Shanahan, Paul Edward.
Cassava (Manihot esculenta Crantz), is the world’s most widely grown starch storage root crop. It is a principal food staple in sub-Saharan Africa where it accounts for approximately one-third of the total production of staple food crops. It plays a key role as a food security and an income-generating crop for millions of smallholder farmers. In Uganda, cassava ranks second to bananas (Musa spp.) in terms of area occupied, total production and per capita consumption; however, nearly 5% of the total population experiences hunger with the prevalence of food energy deficiency at the country level standing at 48%. Cassava is a crop with high potential to alleviate food shortages and energy deficiencies, owing to its unique advantages of producing acceptable yields and starch on infertile soils amidst erratic rainfall, when most other crops would fail. Hoewever, its yield potential has not been fully realised since most of the cassava cultivars grown are susceptible to pests and diseases, low yielding and late bulking. The main objective of the research was to develop high yielding, early bulking cassava genotypes that combine resistance to cassava brown streak disease (CBSD) and cassava mosaic disease (CMD) with farmer preferred traits for cultivation in Uganda. The specific objectives were to: (i) evaluate farmers’ attitudes to and/or perceptions of cassava early bulking, production constraints and cultivar preferences; (ii) determine the extent of genetic variability in storage root bulking and other important traits of selected cassava genotypes; (iii) assess the effects of genotype x environment interaction on early bulking and related traits of selected cassava genotypes; (iv) develop and evaluate cassava F1 families for early bulking in terms of the attainment of early, high fresh storage root yield (FSRY) and resistance to CBSD and CMD; and (v) determine the combining ability and gene action controlling early bulking and yield-related traits, as well as resistance to CBSD and CMD. Through the farmer participatory survey, a number of cassava production constraints were identified, key of which were: diseases, especially CBSD and CMD; lack of early bulking cultivars; rodents and insect pests. Farmers rated early bulking as the second most important preferred trait after FSRY, but suggested that early bulking should be complemented with high dry mass content (DMC), sweetness, high FSRY and resistance to pests and diseases. The analysis of variance of 12 cassava genotypes selected for evaluation in three diverse locations and at five different harvest times indicated significant variation among genotypes, harvest times, locations and their interactions for FSRY and most of the other traits evaluated. Fresh storage root yield and the other traits evaluated were predominantly under the control of genetic variation, indicating that genetic advance would be achieved through hybridisation of the test genotypes. Additive main effects and multiplicative interaction (AMMI) analysis of the data collected at nine months after planting (MAP) indicated a non-significant GEI for early FSRY, but significant GEI for other traits assessed. Eight of the 12 genotypes analysed had relatively low interaction with locations for early FSRY, signifying that these genotypes were relatively stable for early FSRY. Thirty-six F1 families were generated from a 9 x 9 diallel and exhibited a high degree of variation between and within families for all the traits assessed at the seedling evaluation stage. Diallel analysis at the seedling evaluation stage at 10 MAP indicated that additive gene effects were predominant in the expression of early FSRY and most of the other traits analysed. At the clonal evaluation stage, the 36 families were assessed for early FSRY at 8 MAP and this trait together with most of the other traits assessed were found to be predominantly under the control of non-additive gene effects. High mid- and better-parent heterosis for early FSRY was recorded in most families at the clonal evaluation stage with NASE3 x Nyara, Nyara x B11 and NASE3 x B11 recording the highest. Selection from the 36 families at the clonal evaluation stage based on farmers’ top two preferred traits, viz. early bulking for FSRY and DMC, plus resistance to CBSD and CMD identified 50 genotypes that had early FSRY of ≥25 t ha-1 at 8 MAP compared to the best parent, CT1 that had 15.9 t ha-1 at 8 MAP. The selected genotypes also had high DMC and dual resistance to CMD and CBSD. Advancement of the selected genotypes should go a long way towards increasing cassava yield per unit time, reducing food shortages and increasing the income of smallholder farmers in Uganda.
Breeding dry bean for resistance to bacterial brown spot disease conditions in South Africa.
(2018) Salegua, Venancio Alexandre.; Melis, Robertus Johannes Maria.
Bacterial brown spot (BBS) disease is a major disease in dry beans in South Africa causing yield losses of up to 55%. The overall goal of the research was to improve dry bean production through identifying high yielding and stable cultivars, with resistance to the BBS disease, classifying or detecting mega environments for dry bean production and to conduct prebreeding trials that will provide information that will contribute to BBS disease breeding in South Africa. Four hundred and twenty three Andean Diversity Panel (ADP) dry bean genotypes were screened for grain yield and BBS disease resistance in three regions. The plants were inoculated with three isolates of BBS strains or inoculum at 21, 28 and 36 days after planting. Disease severity was rated at 7, 14 and 21 days after the first infection and the relative area under disease progress curve (RAUDPC) was calculated. The analysis of variance revealed significant differences (P<0.001) in grain yield and BBS severity for genotype, environment and genotype by environment interaction (GEI). Genotypes were classified as resistant, moderate resistant and susceptible based on BBS severity and RAUPDC. The study identified 21.0% of the genotypes as resistant and 41.6% as moderately resistant to BBS disease. The RAUDPC was significantly (P<0.001) negatively associated with grain yield (r= -0.55). The small seeded genotypes showed lower RAUDPC than the medium and the large seeded, and genotypes with an indeterminate growth habit showed lower RAUDPC than those with a determinate growth habit. Genotypes ADP-0592, ADP-0790, ADP-0120 and ADP-0008 were selected for both resistance to BBS disease resistance and high seed yield across three environments. The best genotypes had grain yield above 1.45 t ha-1 across sites, and above1.85 t ha-1 at individual sites, and had grain yield above the grand mean (0.87 t ha-1) and the best performing cultivar (1.13 t ha-1), and mean BBS severity below the grand mean (39.85) and the best performing cultivar (31.67). These genotypes can be useful sources of genetic resistance for future dry bean improvement.
Breeding for ascochyta blight [Phoma exigua var. diversispora (Bubak) Boerema] resistance of the common bean (Phaseolus vulgaris L.) in Rwanda.
(2017) Urinzwenimana, Clement.; Melis, Robertus Johannes Maria.; Sibiya, Julia.
Abstract available in PDF file.
Breeding for Cassava brown streak resistance in coastal Kenya.
(2008) Munga, Theresia Luvuno.; Melis, Robertus Johannes Maria.; Shanahan, Paul Edward.; Laing, Mark Delmege.
Cassava (Manihot esculenta Crantz ssp. esculenta) is the second most important food crop and a main source of income for the rural communities with potential for industrial use in the coastal region of Kenya. However, its productivity of 5 to 9 t ha-1 is low due to the low yield potential of the local cassava landraces caused by cassava brown streak disease (CBSD) among other biotic and abiotic constraints. Breeding for CBSD resistant varieties with farmer desired characteristics is hampered by limited information on the current status of the disease and farmers’ preferred characteristics of new CBSD resistant genotypes. In addition, there is a lack of an effective inoculation technique for cassava brown streak virus (CBSV) for screening genotypes for CBSD resistance. Information about the general combining ability (GCA) and specific combining ability (SCA) for CBSD above and below ground symptoms, fresh biomass yield (FBY) and fresh storage root yield (FSRY) (kg plant-1), harvest index (HI), dry matter % (DM %) and picrate score (PS) is limited and conflicting especially for the cassava germplasm in Kenya. These studies were carried out to update information on the status of CBSD, farmer’s preferences for cassava genotypes, and identify the most effective CBSV inoculation technique. In addition, the studies aimed to: determine the GCA and SCA for, and gene action controlling, the incidence and severity of above ground CBSD, root necrosis, FBY, FSRY, HI, DM %, and PS; and identify CBSD resistant progeny with farmers’ desired characteristics. A survey carried out in three major cassava-growing divisions in Kilifi, Kwale and Malindi Districts indicated that there was potential to increase production and productivity by increasing the area under cassava production and developing CBSD resistant genotypes that are early maturing, high yielding and sweet. In addition, CBSD was widely distributed, being present in 98.0% of the farms surveyed at a mean incidence of 61.2%. However, 99.0% of farmers interviewed lacked awareness and correct information about the disease. The genetic variability of cassava within the farms was low as the majority of farmers grew one or two landraces. Highly significant differences (P < 0.01) were observed among inoculation techniques for CBSV for which the highest infection rate of up to 92.0% was observed in plants inoculated by wedge grafting infected scion. Highly significant differences (P < 0.01) were observed among genotypes, between sites and their interaction for incidence of CBSD and root necrosis, while the differences among genotypes and the interaction between genotypes and the period of ratings were highly significant (P < 0.01) for the severity of CBSD and root necrosis. Above ground CBSD symptoms were not always associated with below ground CBSD symptoms and below ground CBSD symptoms were more severe at 12 months after planting (MAP) than at 6 MAP. Therefore, selecting cassava genotypes with resistance to below ground CBSD is more important than selection based on resistance to above ground CBSD and should be done after 12 months. Genotypes 5318/3 (exotic) followed by Msa140 and Plot4 (both local) had high resistance and can be used as new sources of resistance to root necrosis. Both GCA and SCA effects were highly significant with GCA sums of squares (SS) predominant over the SCA SS for most traits evaluated except for DM % at the clonal stage. These results indicate that although additive and non-additive genetic effects are involved in the inheritance of these traits, the additive genetic effects are more important except for DM %. Therefore breeding for CBSD-resistant genotypes that have characteristics desired by farmers in the coastal region of Kenya can be achieved through recurrent selection and gene pyramiding followed by participatory selection or use of a selection index that incorporates characteristics considered important by farmers.
Breeding for durable resistance to angular leaf spot (Pseudocercospora griseola) in common bean (Phaseolus vulgaris) in Kenya.
(2014) Njoki, Ng'ayu-Wanjau Beatrice.; Melis, Robertus Johannes Maria.; Mwangi, Githiri.; Sibiya, Julia.
Common bean (Phaseolus vulgaris L.) is an important legume crop in Kenya and is a cheap source of proteins. The small scale farmers in Kenya produce common bean under low agricultural input systems and this predisposes the crop to pests and diseases. Among the diseases, angular leaf spot (ALS) is a major constraint to common bean production and contributes to yield losses as high as 80%. The causative pathogen Pseudocercospora griseola (Sacc.) Crous & Braun is highly variable and several races have been reported. There are few common bean genotypes with resistance to this disease. Therefore breeding for resistance to ALS is important for the country. This study was carried out to; i) evaluate the common bean production systems, constraints and farmer varietal preferences in Kenya, ii) evaluate local landraces and selected introductions of common bean for yield performance and reaction to ALS, iii) study the genetics of resistance to ALS in common bean and iv) develop a breeding method for durable resistance to ALS in common bean. To determine the common bean production systems, farmers’ preferred traits and their knowledge on common bean constraints including ALS, a survey was conducted in Kiambu county using a semi-structured questionnaire, interviews, and focus group discussions. The study revealed that farmers cultivate common beans during the short and long rain seasons. However, they experience better yields in the short rains due to reduced disease incidence. The majority of the farmers (71%) intercrop common bean and this ensures maximum utilisation of space. A high percentage (70%) of the farmers utilise their retained seed for production. The farmers identified ALS as one of the most important constraints to production. The only preventative measure they undertake to control the disease is weeding. The farmers reported that they would prefer improved varieties that were resistant to ALS. Farmers have a preference for particular common bean traits that include high yield (80%), resistance to insect-pests and diseases (72%), type I growth habit (52%), early maturity (68%), seed size and colour (21%) and cooking time (20%). These should be incorporated in breeding programmes. Two hundred common bean landraces and market class varieties were evaluated for ALS resistance in a nethouse at University of Nairobi, Kabete Field Station and for ALS resistance and yield in the field in KARI-Tigoni. The results showed that disease severity scores for the genotypes were similar in the two locations, with the top three resistant genotypes being Minoire, GBK 028123 and Murangazi with disease severity scores of 2.9, 2.9 and 3.2 in Kabete and 2.6, 2.8, and 2.9 in Thika respectively. These resistant genotypes can be used as sources of resistance in a breeding programme or they can be used as resistant varieties. All the market class varieties were susceptible to ALS (disease severity score 6.7-8.0). There was a non-significant correlation between disease and yield most likely because most of the resistant genotypes were exotic and hence not adapted to the local conditions. There was also a non-significant correlation between disease and seed size. The two hundred common bean genotypes were evaluated for yield at University of Nairobi, Kabete Field Station and KARI-Thika. The results indicated that the 2011 and 2012 seasons had similar mean yields and that yields at Kabete were higher than at KARI-Thika. The highest yielding genotypes across the two locations were; GLP 2 (766 kg ha-1), Nyirakanyobure (660 kg ha-1), GBK 028110 (654 kg ha-1), GLP 585 (630 kg ha-1) and Mukwararaye (630 kg ha-1). There was a significant genotype x environment interaction and hence it is important for breeders to carry out stability analysis, so as to recommend varieties for a wide range of environments. To study the genetics of ALS resistance in common bean, three inter-gene pool crosses: Super-rosecoco x Mexico 54, Wairimu x G10909 and Wairimu x Mexico 54 were made. The resistant genotypes were Mexico 54 and G10909, while Super-rosecoco and Wairimu were susceptible. The generations F1, F2, BC1P1 and BC1P2 for each of the crosses were developed. The parents P1, P2 and the five generations of each cross were evaluated for resistance to ALS in Kabete Field Station. Results showed that both dominance and additive gene action were important in the expression of resistance to ALS. However, additive gene action was predominant over dominance gene action. There was a moderately high narrow sense heritability estimate (52.9-71.7%). The minimum number of genes controlling resistance to ALS was between 2 and 3. The predominance of additive gene effects and the moderately high narrow sense heritability estimates recorded imply that progress in resistance to ALS could be made through selection in the early segregating generations. A double cross followed by selection against resistant genotypes was used to develop a method to breed for durable resistance to ALS in common bean. The method was used to accumulate minor genes of ALS resistance into single genotypes. Four intermediate resistant landraces were used to develop a double cross population that was screened using a mixture of ALS races. Selection in F1 and F2 population was done on the basis of intermediate resistance (disease severity score 4.0-6.0), while selection from F3 population was based on resistance (disease severity score 1.0-3.0). Ten advanced F4 lines along with their parents were evaluated for ALS resistance. The F4 advanced lines had a significantly improved resistance to ALS compared to their parents. Hence the method was successful in accumulating minor genes for resistance thus showing significant breeding progress in breeding for durable resistance.
Breeding for durable resistance to Cercospora Leaf Spot diseases in groundnuts (Arachis hypogaea L.) in Tanzania.
(2018) Kongola, Eliud Francis.; Sibiya, Julia.; Melis, Robertus Johannes Maria.
Lack of high yielding groundnut cultivars tolerant to Cercospora leaf spot disease (CLD) and stable across different environments is one of the challenges to groundnut production by smallholder farmers in Tanzania. This makes selection of adaptable high yielding stable varieties under the different agro-ecological zones before release a very important part of the breeding program as this has an impact on the adoption and productivity of the cultivar. The objectives of this study were to evaluate and select genotypes that are tolerant to CLD, high yielding and identify environments that can be used for selection. A total of 24 groundnut genotypes comprising of six double cross population, twelve single cross parents and six checks from the three botanical groups (Valencia, Virginia and Spanish) were evaluated over six environments (viz Tumbi in Tabora region, Mlali, Ilindi and Hombolo in Dodoma region, Njoro in Manyara region and Ikhanoda in Singida region in Tanzania in the 2016/17 cropping season. The experiment was laid out in a 6x4 alpha lattice design replicated twice. Additive main effect and multiplicative interaction (AMMI) model was used in analysis. The study result revealed that, Tumbi (E1) was the most discriminating environment followed by Ilindi (E3), Mlali (E2), Hombolo (E4), Njoro (E5) and Ikhanoda (E6) respectively. The Hombolo (E4), Njoro (E5) and Ikhanoda (E6) environments showed a high correlation, therefore, indirect selection can be applied across the environments. The existence of such unique correlation among test environments has the advantage of reducing the number of sites used for evaluation and thus reducing cost of evaluating the genotypes. Using the first and second interaction principal component axis (IPCA1 and IPCA 2) genotype G2, G5, G11, G7, G3 and G8 was identified as the best performing genotypes however, G7 had relative stability and adaptability across the testing environments. These crosses will be advanced through selfing and selection of CLD tolerant progenies that are yielding high. Key words: AMMI, Cercospora leaf spot disease, Environments, Groundnuts, IPCA1, IPCA2, Stability, Adaptability.
Breeding of sweet potato (Ipomoea batatas (L.) Lam.) for storage root yield and resistance to Alternaria leaf petiole and stem blight (Alternaria spp.) in Uganda.
(2013) Sseruwu, Godfrey.; Shanahan, Paul Edward.; Melis, Robertus Johannes Maria.
Alternaria leaf petiole and stem blight is an important disease of sweetpotato (Ipomoea batatas (L.) Lam.) causing yield losses in both landraces and improved cultivars. The most important species causing economic yield loss in Uganda are Alternaria bataticola and A. alternate with A. bataticola the most aggressive and widely distributed. The study was conducted to: i) establish farmer-preferred sweet potato attributes, production constraints and Alternaria leaf petiole and stem blight awareness; ii) evaluate Ugandan sweet potato germplasm for Alternaria leaf petiole and stem blight resistance; iii) determine the mode of inheritance of resistance to Alternaria leaf petiole and stem blight and storage root yield components of sweet potato through estimation of the general combining ability (GCA) of the parents and the specific combining ability (SCA) of the parents for each cross; and iv) determine the adaptability and farmer acceptability of selected F1 genotypes across environments. The participatory rural appraisal was conducted to establish farmer preferences and production constraints revealed that farmer preferred sweet-potato traits were high yield, sweetness (taste), early maturity, high dry mass, resistance to pests and diseases, and in-field root storability after maturity. A majority of the farmers considered Alternaria leaf petiole and stem blight a serious production constraint causing yield loss of over 50%. The main control measures against the disease were roguing of infected plants, spraying with fungicides, use of healthy planting materials and planting resistant genotypes. Thirty sweet potato land races and improved cultivars were evaluated for Alternaria blight severity; yield, dry mass, harvest index, sweetpotato weevil (Cylas spp.) damage and sweetpotato virus disease at two sites (Namulonge and Kachwekano) over three seasons (2010B, 2011A, 2011B) under Alternaria inoculum and fungicide spray treatments. Landrace Shock was more resistant to Alternaria blight than Tanzania, the resistant check. Genotypes NASPOT 1, NASPOT 7, New Kawogo and Dimbuka were the most susceptible. Thirty two F1 families were generated from 16 parents in two sets in a North Carolina II mating scheme. The families were evaluated at two sites using a 5 x 7 row-column design with two replications. There were significant (P<0.05) differences among the families in Alternaria blight severity. Both GCA and SCA mean squares (MS) for Alternaria blight were highly significant (P<0.001) but the predominance of GCA sum of squares (SS) for Alternaria blight at 67.4% of the treatment SS versus 32.6% for SCA SS indicated that additive effects were more important than the non-additive effects in controlling this trait. For the yield components, the GCA MS were significant (P<0.05) and accounted for more than 60% of the treatment SS except for percentage dry mass composition where SCA SS accounted for 53.0% of the treatment SS implying that non-additive genetic effects were slightly more important than additive for this trait. Some parents that had desirable high, negative GCA effects for Alternaria blight produced families with undesirable positive SCA effects and the reverse was also true. This implied that the best parents should not be chosen based on GCA effects alone but also on SCA effects of their best crosses. The promising F1 genotypes selected from previously evaluated crosses together with one Alternaria blight resistant check (Tanzania) and one susceptible check (NASPOT 1) were evaluated at three sites (Namulonge, Kachwekano and Serere) using a randomised complete block design with three replications. Scientists and farmers evaluated the agronomic performance and also quality traits of the genotypes before and at harvest. Genotypes G14, G16, G24, G29, G49, G59 and G69 were the most stable across the sites for low Alternaria blight severity and can, therefore, be recommended for further evaluation under both low and high disease pressure areas. Genotypes G67, G13, G14, G24, G29 and G53 were the most high yielding and stable across the sites and were therefore the most widely adapted. In the participatory selection, before harvest and at harvest, Spearman’s rank correlation of the scientists and farmers’ mean ranking of the genotypes at each site was positive and significant. This indicated that the scientists in the study were capable of selecting for farmer preferred traits.
Breeding, evaluation and selection of Cassava for high starch content and yield in Tanzania.
(2009) Mtunda, Kiddo J.; Shanahan, Paul Edward.; Melis, Robertus Johannes Maria.
High starch content is an important component of root quantity and quality for almost all uses of cassava (flour, chips, and industrial raw material). However, there is scanty information on genetic variability for dry matter and starch contents and relatively little attention has been paid to genetic improvement of root dry matter content and starch content in Tanzania. The major objective of this research was to develop improved cassava varieties that are high yielding, with high dry matter and starch content for Tanzania and specifically to: i) identify farmers’ preferences and selection criteria for cassava storage root quality characteristics and other traits of agronomic relevance for research intervention through a participatory rural appraisal; ii) determine the genotypic variability for starch quantity and dry matter content evaluated for three harvesting times in four sites; iii) determine the inheritance of dry matter and starch content in cassava genotypes; and iv) develop and evaluate clones for high storage root yield, high dry matter content and starch. Attributes desired by farmers were yield, earliness, tolerance to pests and diseases. The complementing attributes associated with culinary qualities were sweetness, good cookability, high dry matter content or mealyness and marketability. The preliminary study conducted to evaluate the variability in root dry matter content (RDMC) and starch quantity and yield of ten cassava cultivars indicated that RDMC ranged from 29 to 40% with the mean of 34.3%. The RDMC at 7 months after planting (MAP) was higher than at 11 and 14 MAP. Starch content (StC) ranged from 20.3% to 24.9% with the mean of 22.8%. The StC differed significantly between cultivars, harvesting time and sites. An increase in StC was observed between 0 and 7 MAP, followed by a decline between 7 and 11 MAP, and finally an increase again noted between 11 and 14 MAP. However, for most of the cultivars at Kibaha an increase in StC between 11 and 14 MAP could not surpass values recorded at 7 MAP. At Kizimbani, cultivar Kalolo and Vumbi could not increase in StC after 11 MAP. At Chambezi and Hombolo, a dramatic gain in StC was observed for most of the cultivars between 11 and 14 MAP. Starch yield ranged from 0.54 to 4.09 t ha-1. Both StC and fresh storage root yield are important traits when selecting for commercial cultivars for starch production. Generation of the F1 population was done using a 10 x 10 half diallel design, followed by evaluation of genotypes using a 4 x 10 á-lattice. Results from the diallel analysis indicated that significant differences in fresh storage root yield (FSRY), fresh biomass (FBM), storage root number (SRN), RDMC, starch content (StC), and starch yield (StY), and cassava brown streak disease root necrosis (CBSRN) were observed between families and progeny. The FSRY for the families ranged from 15.0 to 36.3 t ha-1; StC ranged from 23.0 to 29.9%; RDMC ranged from 31.4 to 40.1%; and StY ranged from 3.3 to 8.3 t ha-1. The cassava mosaic disease (CMD) severity ranged from 1.7 to 2.7, while cassava brown streak disease (CBSD) severity for above ground symptoms ranged from 1.0 to 1.9. Additive genetic effects were predominant over non-additive genetic effects for RDMC, StC, and CBSRN, while for FSRY, FBM, SRN, and StY non-additive genetic effects predominated. Negative and non-significant correlation between RDMC and FSRY was observed at the seedling stage (r=-0.018), while at clonal stage the correlation was positive but not significant (0.01). The RDMC and StC were positive and significantly correlated (r=0.55***) at clonal stage. However, the StC negatively and non-significantly correlated with FSRY (r=- 0.01). High, positive and significant correlation (r=0.94; p.0.001) was observed between the StY and FSRY at clonal stage. High, positive and significant correlations between the seedling and clonal stage in FSRM (r=0.50; p.0.01), RDMC (r=0.67; p.0.001), HI (r=0.69; p.0.001), and SRN (r=0.52; p.0.01) were observed, suggesting that indirect selection could start at seedling stage for FSRM, RDMC, HI, and SRN. The best overall genotype for StC was 6256 (40.9%) from family Kiroba x Namikonga followed by genotype 6731 (40.6%; Vumbi x Namikonga). Among the parents, Kiroba and Namikonga were identified as the best combiners in terms of GCA effects for StC. Genotype 6879 from family Vumbi x AR 42-3 had the highest StY value of 34.8 t ha-1 followed by genotype 6086 (30.4 t ha-1; Kalolo x AR 40-6). Among the parents, Kalolo and AR 42-3 were identified as good combiners for the trait. Mid-parent heterosis for StC ranged from 41.6 to 134.1%, while best parent heterosis ranged from 30.4 to 119.6%. Genotype KBH/08/6807 from family Vumbi x TMS 30001 had the highest mid-and best parent heterosis percentage for StC. For StY, mid-parent and best parent heterosis ranged from 168.0 to 1391.0%, and from 140.4 to 1079.0%, respectively, with the genotype 6879 (Vumbi x AR 42-3) exhibiting the highest mid- and best parent heterosis percentage for StY. Improvement for StC, RDMC, and CBSRN may be realized by selecting parents with the highest GCA effects for the traits and hybridize with those that combine well to maximize the positive SCA effects for the StC, RDMC and CBSRN. Selected genotypes from the clonal stage will be evaluated in preliminary yield trial and advanced further to multi-locational trials while implementing participatory approaches involving farmers and processors in selection. New promising lines should be tested at different sites and the best harvesting dates should be established.
Cassava breeding through complementary conventional and participatory approaches in western Kenya.
(2011) Were, Woyengo Vincent.; Melis, Robertus Johannes Maria.; Shanahan, Paul Edward.
Participation of farmers in plant breeding programmes has been reported to increase breeding efficiency. Farmers’ participation bridges the gap between variety development and dissemination and provides an opportunity for farmers to select varieties they prefer. The breeders on the others hand learn more about the farmers’ preferences and the environment in which the new varieties will be grown. However, the advantages of participatory breeding can best be realized when farmers’ indigenous technical knowledge (ITK) and experience complement the breeder’s scientific knowledge and skills. Cassava (Manihot esculenta Crantz) is a clonally propagated crop grown in diverse environments by small scale farmers for subsistence. Information on the roles of farmers and breeders at various stages of breeding and their ability to effectively participate in breeding programmes is limited. The objectives of this study were to determine: (1) cassava farmers’ preferences, production constraints and systems; (2) farmers’ selection criteria of cassava varieties; (3) genetic inheritance of farmer preferred traits; (4) how farmers and breeders complement each other at all stages and activities of cassava breeding. Participatory rural appraisal was conducted in three purposefully sampled districts of western Kenya based on ethnicity and agro-ecology. The results reveal that cassava is predominantly grown by small scale farmers with mean land size of 1.6 ha mainly under mixed cropping system for subsistence. The storage roots are eaten either after boiling or processing to flour. The majority of farmers (over 60%) are aware of the improved varieties but adoption rate is low (18% in some districts). The effects of pests and diseases, and the lack of high yielding varieties, capital, land, and disease free planting material are the most important constraints to cassava production. Farmers prefer tall, high yielding varieties that are resistant to diseases and pests, early maturing and long underground storability of harvestable storage roots. The districts surveyed significantly differed in popularity of utilization methods, traits preferences and relative ranking of the production constraints indicative of differences in ethnicity and agro-ecology. Three farmer groups from the three districts selected in western Kenya were used to study farmers’ variety selection criteria based on their own indigenous technical knowledge (ITK). The groups evaluated 15 (10 landraces and five improved) popular cassava varieties with concealed identities on their farms. The results revealed that farmers have effective methods of selecting varieties for most of their preferred traits. However, ITK alone cannot be used to evaluate all the important traits, such as cyanide content. The genetic inheritance of farmer preferred traits was determined through a genetic study. Six landraces and four improved varieties popular in western Kenya were crossed using the North Carolina mating design II to generate 24 full-sib families. The 24 families, represented by 40 siblings each, were evaluated at two sites, Kakamega and Alupe research station farms, in a 24 x 40 a-lattice design. General combining ability (GCA) and specific combining ability (SCA) mean squares were significant (P<0.05) for all traits evaluated except dry matter content and cyanide content. However, non-additive gene action predominated over additive gene for cassava mosaic disease (CMD) resistance, height to first branching, total number of storage roots per plant and fresh storage root yield in all environments. The best crosses were not necessarily obtained from parents with high general combining ability confirming the presence of non-additive gene action. The best performing parents per se did not necessarily have high GCA effects implying that selection based on the per se performance of parents may not always lead to development of superior hybrids. The clonal evaluation trial (CET) was established at Alupe research station and evaluated by the breeder and farmers from two districts independently. Three selection criteria were tested to determine the most appropriate approach to selection of varieties that meet both farmers’ and breeder’s preferences. The selection criteria were; farmers’ independent selection index (SI) derived from farmers’ selection criteria from each district, breeder’s negative selection and independent SI, and a participatory SI which combines farmers’ and breeder’s selection criteria. There was 14% overlap among the top 100 varieties selected by farmers from all districts and the breeder when independent SI were used. However, there was 49% overlap among the top 100 varieties selected by farmers using participatory SI and the breeder’s SI. The farmers and the breeder have a role to play in the variety development process. Varieties with traits preferred by both the farmers and the breeder are likely to enhance breeding efficiency and effectiveness.
Development of cassava (Manihot esculenta Crantz) cultivars for resistance to cassava mosaic disease in Zambia.
(2011) Chikoti, Patrick Chiza.; Melis, Robertus Johannes Maria.; Shanahan, Paul Edward.; Chisi, M.
Despite the increasing number of farmers growing cassava in Zambia, yield per hectare has remained low at 5.8 t ha-1. The major constraints contributing to low yields are pests and diseases of which cassava mosaic disease (CMD) caused by East Africa cassava mosaic virus (EACMV), Africa cassava mosaic virus (ACMV) and South Africa mosaic virus (SACMV) is the most important. Breeding of cassava is restricted by limited information on viruses and associated satellites, and farmer preferences. Most of the farmers cannot manage to institute control strategies that require buying of chemicals. The most feasible option remains improving existing cultivars through resistance breeding. The study therefore was conducted to: i) establish farmers’ perception and knowledge of CMD; ii) to identify viruses of cassava occurring in Luapula province; iii) evaluate the performance of local and improved cultivars for agronomic traits; iv) evaluate the performance of F1 progenies for CMD resistance; and v) determine general combining ability and specific combining ability for CMD resistance. The studies were carried out between 2008 and 2011 at different locations in Zambia. The information generated was important in formulating a local breeding strategy for CMD resistance. A participatory rural appraisal and a structured survey was conducted in Mansa, Samfya and Mwense districts in Luapula province involving farmers to ascertain farmers’ perceptions of CMD. The results of the study showed that the majority of the respondents (97.6%) were not aware of CMD. Most of the farmers grew landraces on small pieces of land. Although, the cultivars (local and improved) were widely grown, they were susceptible to CMD. The farmers preferred cultivars with high yielding and early bulking characteristics among others. A CMD survey conducted between April and May 2009 in Samfya, Mansa, Mwense, Kawambwa and Nchelenge districts in Luapula province established East Africa cassava mosaic virus (EACMV), and Africa cassava mosaic virus (ACMV) as the most prominent viruses in the area. Symptoms of satellites were also observed in the farmers’ fields in most of the areas visited. Satellite II and III were detected in leaf samples. The CMD incidence (59.1%) and severity (2.4) was moderate across the districts surveyed. The CMD symptoms on the cassava plants were variable with plants showing mild and severe symptoms characterised with narrowing and reduced leaf blades. The transmission of CMD infections was mainly through cuttings rather than via whitefly infection which means that most of the planting materials used by the farmers were infected. Evaluation of cassava cultivars for CMD resistance was conducted in 2009/2010 and 2010/11 seasons at Mansa Research Station in Luapula province using a 4 x 4 α lattice design. Both introduced and locally grown cultivars had significant (P<0.001) differences in their reaction to CMD. Bangweulu, Namuyongo, Kalaba, Chikula, Mwakamoya, Chila7 and Chila11 were the most susceptible genotypes. Mweru, Tanganyika, and Nalumino were moderately tolerant to CMD. Eight hundred F1 genotypes developed using a North Carolina II mating design were evaluated in a 4 x 5 α lattice design in 2011 at Mansa Research Station, Luapula province to determine combining ability for reaction to CMD, yield and yield components. The plants were harvested 7 months after planting (MAP). Significant (P<0.001) general combining ability and specific general combining ability were recorded for CMD. The SCA effects were more important for CMD than GCA effects suggesting that non-additive gene action was more prominent than the additive gene action in determining CMD reaction. Parent lines with desired significant, negative GCA effects for reaction to CMD were Bangweulu, Kampolombo, Nalumino and TME2. In general, the survey and participatory rural appraisal established CMD as one of the constraints to cassava production and created a basis for the research study. The findings indicate opportunities that exist in creating genotypes with tolerance to CMD. The study identified cassava lines with resistance to CMD. The lines that expressed the above trait should be selected and tested further for release to the farmers in Zambia. Since the clonal evaluation trial was harvested at 7 MAP, there is need to investigate further for earliness trait in best performing lines in different locations.
Development of high yielding and early maturing potato (Solanum tuberosum L.) genotypes with resistance to Phytophthora infestans in Uganda.
(2017) Namugga, Prossy.; Sibiya, Julia.; Melis, Robertus Johannes Maria.
Abstract available in PDF file.
Development of high yielding potato (Solanum tuberosum L.) : genotypes with resistance to bacterial wilt (Ralstonia solanacearum) for the Kenyan highlands.
(2014) Mbugua, Jane Muthoni.; Hussein, Shimelis.; Melis, Robertus Johannes Maria.
Bacterial wilt caused by Ralstonia solanacearum race 3 (R3bv2A), is an important disease contributing to low potato yields in temperate areas and tropical highlands. In Kenya, the disease is widespread in most potato growing areas causing yield losses between 50 and 100%. Host plant resistance could be the best option for controlling the disease because other measures are costly, ineffective or impractical to deploy. The overall objective of this study was to contribute to improved food security in Kenya by developing potato cultivars that are resistant to bacterial wilt. The specific objectives of the study were to: (1) document farmers‘ practices, key potato production and marketing constraints, and to determine farmers‘ potato cultivar preferences, the prevalence of bacterial wilt in the major potato growing areas and farmers‘ management practices of bacterial wilt, (2) determine the response of the potato genotypes currently grown by farmers in Kenya as well as other clones from the international Potato Center (CIP) to bacterial wilt, (3) determine the genetic relationships among potato clones,(4) determine the combining ability effects for yield and yield related traits and bacterial wilt resistance of selected potato varieties and clones and their crosses, and (5) to estimate the magnitude of genotype x environment interaction (GEI) for potato tuber yield and bacterial wilt resistance. At the beginning, a participatory rural appraisal (PRA) was conducted in three major potato growing counties involving 253 potato growers in Kenya. Farmers varied in cultivar and trait preferences; in Bomet district the red-skinned Dutch Robyjn is widely grown. In Molo district, the white-skinned Cangi is prominent while in Meru Central, the red-skinned Asante is predominantly grown by farmers. The cultivar preferences are mostly dictated by availability of markets, yield potential and taste. Over 75% of respondents indicated that the major production constraints are diseases with bacterial wilt being the most prominent. Farmers use different methods in managing the disease in the field such as spraying with fungicides, roguing and burning the wilting plants, and burying of the rotten tubers after harvest. Field experiments were conducted to evaluate 36 potato genotypes for their response to bacterial wilt for three consecutive seasons between November 2011 and February 2013. The potato genotypes varied in their susceptibility to bacterial ii wilt and the most resistant genotypes were Kenya Karibu followed by Kenya Sifa. Twenty selected potato genotypes were evaluated for genetic variability using 24 SSR primer pairs selected based on high polymorphism. The SSR markers identified 160 alleles.The 20 potato clones were grouped into 3 clusters. Cluster I was composed of Meru Mugaruro, cluster II had CIP materials while local materials were in cluster III. Therefore, the SSR markers generated useful information that will assist in identifying parents to include in the breeding programme. Fourteen potato genotypes were identified as promising parents for further breeding based on their resistance to bacterial wilt. These parents were crossed in a North Carolina II mating design to generate 48 families for determining combining ability. Parents with highest general combining ability for bacterial wilt resistance were Ingabire, Meru Mugaruro, 391919.3, 394895.7 and 394903.5. These parents were selected for future crosses. In addition, nine crosses with the highest SCA effects for total tuber yield (TTW) at Kenya Agricultural Research Institute, National Research Laboratories (KARI-NARL) were 394905.8 x Kihoro (31.94), 394903.5 x Kenya Karibu (31.46), 394904.9 x Meru Mugaruro (25.73), 394895.7 x Bishop Gitonga (15.37), 394905.8 x Cangi (13.06), 394895.7 x Tigoni (12.23), 394904.9 x Sherekea (11.44), 394895.7 x Sherekea (10.92) and 391919.3 x Tigoni (10.32) in that order. At Kinale, the nine crosses with the highest SCA effects for TTW were 394905.8 x Kihoro (27.13), 394903.5 x Kenya Karibu (24.37), 394904.9 x Meru Mugaruro (19.59), 394895.7 x Cangi (15.69), 3948957 x Bishop Gitonga (15.35), 394895.7 x Tigoni (11.93), 394904.9 x Sherekea (9.36), 392278.19 x Meru Mugaruro (9.10) and 391919.3 x Cangi (7.64) in that order. These crosses were selected for high tuber yield and will be evaluated in future. The GEI effects on 48 potato families were evaluated at two sites for two consecutive seasons (making a total of four environments). The potato families were ranked differently in terms of resistance against bacterial wilt across the four environments. The additive main effects and multiplicative interaction (AMMI) 1 and genotype and genotype x environment (GGE) biplot models were used to determine yield stability. In terms of yield stability, family 20 (394905.8 x Kihoro) was closest to the ideal genotype; it was the highest yielding (104.7 t ha-1) and most stable; it was closely followed by family 43 (394903.5 x Kenya Karibu) which yielded 98.3 t ha-1. The environment ENVI 1(short rains of 2013 at Kinale) was the closest to ideal environment and therefore the most desirable of the four test environments. In general, the study identified valuable potato genotypes with high combining ability for tuber yield and bacterial wilt resistance. It also generated novel families which will be further evaluated.
Development of pigeonpea [Cajanus cajan (L.)] hybrids for the semi-arid Kenya.
(2011) Makelo, Margaret Nafula.; Melis, Robertus Johannes Maria.; Mwangi, Githiri.
Pigeonpea (Cajanus cajan (L.) Millsp.) is cultivated by many farmers in the semi-arid areas of Kenya as a source of food and cash. However, the yields have remained low, ranging between 500 to 800 kg haˉ¹. Apart from drought, fusarium wilt is reported to affect yield. Breeding pigeonpea hybrids, using cytoplasmic male sterile (CMS) lines, hybridized with the local improved germplasm, have the potential for increasing yield and improve income for smallholder farmers. The objectives of the study were to: 1) examine the various stakeholders of the pigeonpea value chain and their core functions and identify characteristics of the pigeonpea varieties preferred by the market to be considered in the hybrid breeding programme, 2) evaluate cytoplasmic male sterile lines of Indian origin for stability across several environments in Kenya, 3) screen pigeonpea genotypes for general resistance to Fusarim udum Butler and 4) evaluate pigeonpea hybrids for grain yield and earliness across sites and seasons in Kenya. The stakeholder analysis established that the main players in the pigeonpea value chain were farmers, traders/processors, International Crops Research Institute for the Semi-Arid Tropics, Kenya Agricultural Research Institute, Kenya Plant Health Inspectorate Services, and Ministry of Agriculture. White seed, large seed size and medium maturity were the preferred traits by farmers and processors/exporters for both domestic and export markets. The unavailability of quality seed in sufficient quantities of high yielding varieties was cited as the main factor negatively affecting pigeonpea production. The stakeholder analysis approach, used for the first time in a breeding programme, demonstrated that it can be an important tool that can be used to diagnose crop production constraints, and define opportunities available for setting up a breeding programme that is highly client-oriented. Two CMS lines, ICPA2043 and ICPA2039 were the most stable across sites with 100% and 99% pollen sterility respectively. Screening for the presence of physiologic races of F. udum based on morphological and cultural characteristics on PDA identified three distinct isolate groups named ISO-A, ISO-B, and ISO-C. Studies under controlled conditions using the three isolates identified seven pigeonpea genotypes (ICPB2043, ICP12012, ICP13092, ICPA2039xICP13092, ICPA2043xICP12012, ICPA2043xICP13092, ICPA2043xICP9135) resistant to the three F. udum isolates. In the field evaluation, seven genotypes (ICPA2039xICP13092, ICPA2039xAsha, ICPA2043x12012, ICPA2043xICP13092, ICPA2043xICEAP557, ICPB2043 and Maruti) were found to be moderately resistant. The variances due to GCA and SCA were significant, showing that both additive and non-additive gene actions were important. The resistant hybrid, ICPA2043xICP12012 had the highest negative SCA that was highly significant for all the isolates and in the field indicating general resistance. The CMS (A) line ICPA2043 was found stable across environments and highly resistant to the three F. udum isolates. Therefore, it can be evaluated further for commercial hybrid seed production in Kenya. Evaluation of the pigeonpea genotypes across environments indicated that the highest yielding environment was Kiboko, with average and maximum yield of 2,249 kg haˉ¹ and 4,234 kg haˉ¹ respectively. Most hybrids were in the medium duration maturity group with days to maturity ranging from 147 to 186. Overall, the highest yielding hybrids were A2043xTZ26 and ICPA2039xTZ24 with mean yields 2,803 kg haˉ¹ and 2,527 kg haˉ¹ respectively. Mean yields for the best performing parents were 2,036 kg haˉ¹ for ICP12012 and 1,629 kg haˉ¹ for Asha. For specific sites, the highest yielding hybrids in Kabete, Kiboko and Leldet were A2039xTZ24 (2,057 kg haˉ¹), A2043xTZ26 (2,803 kg haˉ¹), and A2043xUG8 (1,708 kg haˉ¹) respectively. Mean heterosis for yield varied from -35% (A2039xA2043) to 50% (A2043xUG8). In Kenya, the potential for production and commercialization of hybrid pigeonpea is feasible due to high hybrid vigour recorded, and the stability of the CMS lines. Hybrids also have greater uniformity in grain size a factor which is important for the market.
Genetic analysis of common bean (Phaseolus vulgaris L.) genotypes for tolerance to drought and heat stress in Zambia.
(2015) Phiri, Nathan.; Tongoona, Pangirayi.; Melis, Robertus Johannes Maria.; Mwangi, Githiri.
Common bean (Phaseolus vulgaris L.) is widely grown and consumed in Zambia but its production is limited by drought and high temperature stresses. In the country there is limited information on farmers’ preferences and the genetics of drought and heat tolerance of common bean for breeding to enhance its production. Therefore, the objectives of this study were to: 1) determine farmers’ selection criteria and preferences for common bean varieties, 2) evaluate the Zambian bean germplasm for drought and heat tolerance, and 3) determine the genetic effects and inheritance of drought and heat stress tolerance in Zambian common bean germplasm. A participatory rural appraisal and survey studies established that the preferred bean varieties by the farmers in Siavonga (Lusitu) and Gwembe districts were of determinate bush type growth habit, red speckled seeds, large and elongated seed shape, early maturing, and prolific with high numbers of pods per plant. Lyambai, a red speckled seed variety, was chosen as their most preferred type meeting most of their selection criteria. It was also established that women were better able to distinguish between common bean varieties in terms of taste and cooking time than men. It was further established that the educated farmers based their variety selections on a background understanding of varietal characteristics. A screening study involving 120 common bean genotypes identified LY4-4-4-B as the most drought tolerant genotype followed by LY1-2-B, ZM 3831, KAL–ZA, SCCI 13, ZM 4512-5 and LYA–ZA based on yield and yield related traits. Two genotypes, a mutant, LY4-4-4-B and a landrace, ZM 3831 were selected among the most drought tolerant genotypes for developing F1 populations used in the genetic study. This study also established that 100-seed weight was not affected by drought stress, probably due to the compensatory effects of reduced numbers of pods per plant and number of seeds per pod. The evaluation of the 120 genotypes under elevated temperatures (>33oC) established that ZM 4143, ZM 4497, SCCI 4, KE 1, and ZM 07, were more tolerant to heat stress. ZM 4143 and ZM 4497 were further selected among the most heat tolerant genotypes for developing F1 populations used in the genetic study. The significant (P≤0.05) GCA effects for 14 parental lines for yield, number of seeds pod-1, and number of pods plant-1 indicated that additive gene effects were important in the inheritance of these traits under heat stress. The significant (P≤0.05) and positive SCA effects for the F2 families of Kapisha X SEN 39, Kapisha X ZM 4497, Kalungu X SEN 39, and Lyambai X ZM 4143 were generated from parental lines with high and positive GCA values indicating their potential for further selection for high temperature tolerance from these populations. Further genetic studies on drought tolerance for the 14 parents and the 48 F2 populations established that ZM 4143 and ZM3831 were drought tolerant male parents with significant (P≤0.05) and high positive GCA effects. The crosses with high SCA values for the F2 population emanating from Chambeshi X ZM 4143, Pan 148 X ZM 4143, Lyambai X SER 124, Chambeshi X ZM 3831, SCCI 2 X Ly 4 -4-4-B, ZM 05 X SER 124 and Lyambai and ZM 3831 had parents with high and positive GCA effects indicating potential for making further selections for drought tolerant genotypes. The high heritability estimate for yield of 60% found in drought stressed conditions also indicated that breeders can make progress in breeding for drought tolerance.
Genetic Improvement of pigeonpea (Cajanus cajan (L.) Millsp.) for Fusarium wilt resistance in Tanzania.
(2016) Kimaro, Didas Rogasian.; Melis, Robertus Johannes Maria.; Sibiya, Julia.
Abstract available in PDF file.
Genetic studies on host plant resistance to Mexican bean weevil (Zabrotes subfasciatus Boheman) in Ethiopian common bean (Phaseolus vulgaris L.) germplasms.
(2017) Girsil, Tigist Shiferaw.; Melis, Robertus Johannes Maria.; Sibiya, Julia.
The common bean (Phaseolus vulgaris L.) is the second most important food legume in Ethiopia. It is the most important cash crop for the smallholder farmers and has a significant impact on the national economy. However, the productivity of the crop is hampered by many biotic and abiotic stress factors. In recent years, the Mexican bean weevil (Zabrotes subfasciatus Boheman), hereafter also called bruchid, has been causing significant grain losses in storage. Therefore, the objectives of the present study are as follows: (a) to evaluate the Ethiopian common bean landrace collections, commercial varieties, advanced breeding lines and elite resistant lines for resistance to the Mexican bean weevil; (b) to assess the magnitude and pattern of genetic diversity in Ethiopian common bean landraces, commercial varieties, advance breeding and exotic resistant lines for the response to infestation by bean bruchid, using phenotypic and SNP markers; (c) to examine the population structure among common bean genotypes collected from different breeding status, seed colours and sizes, and to identify genomic regions that are associated with bean bruchid resistance, using SNP markers distributed across common bean genome; (d) to assess the agronomic performance of common bean genotypes selected for their response to bruchid infestation, using yield and yield components under different agro-ecologies; (e) to identify suitable parental genotypes that are useful for breeding for bruchid resistance and to identify the farmers’ selection criteria for choosing varieties; and (f) to interogress arcelin genes into commercial varieties and an advanced breeding line. For this study, a total of 300 common bean genotypes were phenotyped for bruchid resistance under laboratory conditions, and they were genotyped, using Illumina BARCBean6K_3 SNP BeadChip. Data on insect and seed traits were used for genetic diversity and genome-wide marker-trait association analysis. One-hundred and-forty-four genotypes were selected, based on their level of resistance, population structure and genetic distances and they were evaluated under three different agro-ecological field conditions, for yield and yield-related traits. Participatory variety selection (PVS) was also conducted for the selected genotypes. Subsequently, six female parents and seven donner lines were selected, based on the farmers’ traits of interest, level of resistance and suitable agronomic traits, of which one commercial variety and one advanced breeding line were crossed with one donor Marker Assisted Zabrotes (MAZ) resistant lines. The segregating population was phenotyped for bruchid resistance at the F4 generation. The laboratory screening of the genotypes revealed that a wide range of variation was recorded among the landraces, commercial varieties, advanced breeding and resistant lines for all the parameters studied. Absolute resistance was recorded only from the resistant lines, namely RAZ-11, RAZ-36, RAZ-2, RAZ-44, RAZ-120, RAZ-40, MAZ-200 and MAZ-203, while the majority of the local germplasm was found to be susceptible. Some of the local germplasm showed a partial resistance to bean bruchid and two promising entries were identified, namely, SCR-11 (breeding line) and NC-16 (landrace). The genetic diversity analysis, using phenotypic and SNP markers, revealed that considerable variation was existed among the Ethiopian common bean genotypes. High phenotypic diversity indices among phenotypic traits were recorded. The principal component analyses identified four PCs that explained 82% of the total phenotypic variation among genotypes. The polymorphic information content (PIC) ranged from 0.21 to 0.38, with a mean 0.34, reflecting the relatively high discriminating ability of the SNP markers. More than 70% of the gene diversity was recorded within the common bean population that were classified according to their breeding status and seed size. The four and two populations that were based on breeding status and seed size, respectively, were highly differentiated. Both the SNP and the phenotypic markers grouped the 297 common bean genotypes into two major distinct clusters and three sub-clusters, irrespective of their geographic origin. The population structure analysis, based on Bayesian genotyping clustering approach, classified the common bean genotypes into two populations, namely, the Middle American and Andean gene pools. Similar population patterns were also observed by using the principal coordinate analysis (PCoA). The genome-wide association study (GWAS) identified 24 single-nucleotide polymorphism (SNP) markers on nine chromosomes, with a significant (P < 0.05) association with a percentage adult emergence (PAE) and a percentage seed weight loss (PSWL). However, only 13 SNPs located on Chromosomes 4 and 7 were significantly (P < 0.001) associated with the two traits. Other significant SNPs were identified on other chromosomes of the common bean, but none of them were above the cutoff point (1.00 × 10−4). Based on the above analyses, 144 diverse genotypes were selected and evaluated at three sites. Six principal components (PCs) were identified that explained 84% of the total variation among the genotypes. The 15 agro-morphological traits classified the genotypes into three distinct major clusters and sub-clusters. The clustering patterns of the genotypes were according to the seed size, in which small and medium beans were distinctly separated from the large seeded beans. The study established the existence of considerable genetic variation among common bean genotypes. Unique genotypes, such as Nasir, Awash Melka and RAZ-36 from Cluster I, RAZ-2, RAZ-11 and RAZ-42 from Cluster II and SER-125, SCR-15, MAZ-200, MAZ-203 and RAZ-120 from Cluster III were selected, based on their distinct agronomic performance and their response to the Mexican bean weevil infestation. The participatory variety selection revealed that farmers used complex and diverse selection criteria in different agro-ecologies. The selection criteria varied among agro-ecologies and gender groups. Yield and yield-related traits were ranked as the most important selection criteria in all the locations and gender groups. Women ranked the taste and cooking time as the top criteria for varietal choice, while men were more interested in marketability, seed size and colour. In all three agro-ecologies, both farmer groups were able to select the top 10 best genotypes, although varietal preferences across locations and gender groups were diverse. The top set of selected genotypes matched the breeders’ selection, with only minor difference. The phenotyping of the F4 families derived from SCR-15 X MAZ-200 crosses showed highly significant differences (P < 0.001) among the entries, parents and offspring for all of the susceptible parameters, except the number of eggs. Based on the percentage adult emergence, 34.6% of the progeny genotypes were categorized as highly resistant, 12.0% were resistant, 21.6% were moderately resistant and 32.7% were susceptible. The study observed considerable phenotypic variation among the offspring and parental lines for the susceptibility parameters. The levels of broad sense heritability ranged from 68.5% – 93.9% for all the traits, suggesting that selection may be useful to improve bruchid resistance. In general, the study has identified absolute resistant lines among the exotic germplasm, while partial resistance genotypes among the Ethiopian genotypes signifies the possibility of the introgression of the resistance genes. The information reported in this study could serve as an important benchmark for future common bean breeding and conservation programs.
Genetic studies on host-plant resistance to bean fly (Ophiomyia spp.) and seed yield in common bean (Phaseolus vulgaris) under semi-arid conditions.
(2010) Ojwang', Pascal Peter Okwiri.; Melis, Robertus Johannes Maria.; Mwangi, Githiri.
Bean fly (Ophiomyia spp.) is a major pest of common bean (Phaseolus vulgaris L.) throughout eastern and southern Africa. In the semi-arid areas, apart from drought, the insect pest is reported to cause high crop losses up to 100%, particularly when drought occurs and under low soil fertility. Host-plant resistance is part of the integrated pest management strategies that have been widely employed against major insect pests of tropical legumes. However, information regarding its use in control of bean fly in common bean is limited. Therefore, the objectives of this study were to: (1) validate farmers’ perceptions of major constraints responsible for yield losses, particularly the major insect pests of beans; (2) asses the level of adoption of improved bean varieties and determine factors that influence farmers’ preferences of the varieties and criteria for selection; (3) identify sources of resistance to bean fly available in landraces; (4) determine the nature of gene action controlling bean fly resistance and seed yield in common bean; (5) describe a procedure for generating optimal bean fly populations for artificial cage screening for study of the mechanisms of resistance available in common bean against bean fly. Farmers considered drought and insect pest problems as main causes for low yields. The adoption rate for improved varieties was high but self-sufficiency in beans stood at 23% in the dry transitional (DT) agro-ecology and at 18% in the dry mid-altitude (DM) agroecology, respectively. Drought, earliness, yield stability, and insect pest resistance were the factors determining the choice of varieties by farmers. Bean fly (Ophiomyia spp.), African bollworm (Helicoverpa armigera) and bean aphid (Aphis fabae) were identified as key crop pests of beans limiting yield. The study to identify new sources of resistance included 64 genotypes consisting of landraces, bean fly resistant lines and local checks. The experiment was done under drought stressed (DS) and non-stressed (NS) environments and two bean fly treatments (insecticide sprayed and natural infestation) for three cropping seasons between 2008 and 2009. Genotypes differed in their reaction to natural bean fly attack under drought stressed (DS) and non-stressed environments (NS) over different cropping seasons. However, the effect of bean fly appeared to vary between the long rains (LR) and short rains (SR). It was observed that an increase in the number of pupae per stem resulted in a higher plant mortality. The range of seed yield was from 345 to1704 kg ha-1 under natural infestation and from 591 to 2659 kg ha-1 under insecticide protection. Seed yield loss ranged from 3 to 69 %. The resistance of most of the bean fly resistant lines seemed to be ineffective in presence of DS. To determine the nature of gene action controlling the inheritance of resistance to bean fly, four parents with known reaction to bean fly were crossed with four locally adapted genotypes in an 8 x 8 half-diallel mating design. Similarly, two resistant and two susceptible parents were selected and crossed to produce populations for generations means and variance components analysis. Results revealed that both general combining ability (GCA) and specific combining ability (SCA) mean squares were significant (p A 0.05) for all four traits studied, except SCA for stem damage during one cropping season. Among the parents, GBK 047858 was the best general combiner for all the traits studied across seasons except for stem damage during LR 2009. Genotypes GBK 047821 and Kat x 69 (a locally adapted variety) were generally good general combiners for resistance traits as well as seed yield. General predictability ratio values ranging from 0.63 to 0.90 were obtained for plant mortality, stem damage, pupae in stem and seed yield across cropping seasons. These results established the predominance of additive gene effects (fixable variation) over the non-additive effects in controlling the traits. Low to moderate narrow sense heritability values ranging from 0.22 to 0.45 were obtained for pupae in stem. Such heritability estimates indicate that although additive gene components were critical in the inheritance of resistance for the trait, non-additive gene action was also important in addition to the environmental effects. A major disadvantage in screening for resistance to bean fly in common bean by controlled means in net cages has been the lack of a method to use for raising adequate fly populations for screening. Due to this problem, a simple procedure for raising sufficient numbers of adult bean flies required for screening was described. Through this method, up to 62 % emergence of the adult flies was achieved. Moreover, the flies retained their ability to infest bean plants. To determine the presence of antibiosis and antixenosis mechanisms of resistance in common bean, five genotypes [CC 888 (G15430), GBK 047821, GBK 047858, Ikinimba and Macho (G22501)] and two local check varieties (Kat B1 and Kat B9) were screened under free-choice in outdoor net cages and no-choice conditions in net cages placed in a shadehouse. All the five resistant genotypes tested had relatively long internodes. It was established that long internode was a morphological trait associated with reduced pupation rate in bean stems, hence an antixenosis component of resistance. Both ovipositional non-preference and antibiosis mechanisms were found to exist in three genotypes namely CC 888 (G45430), GBK 047858 and Macho (G22501). These genotypes were resistant when they were subjected to bean fly under both free-choice and no-choice conditions. They had fewer feeding/oviposition punctures, low number of pupae in the stem, reduced damage to the stems and low percent plant mortality. The remaining genotypes, Ikinimba and GBK 047821 only expressed antixenosis. To maximize the effectiveness of host-plant resistance against bean fly, multiple insect resistances should be incorporated into a single bean genotype in order to ensure durability. However, this should be within the background of integrated pest management strategy.
Genetic study of cowpea (Vigna unguiculata (L.) Walp) resistance to Striga gesnerioides (Willd.) vatke in Burkina Faso.
(2010) Tignegre, Jean Baptiste De La Salle.; Melis, Robertus Johannes Maria.; Tongoona, Pangirayi.
In Burkina Faso, the existence of different races of Striga gesnerioides (Willd.) Vatke, with apparent variable aggressiveness on cowpea (Vigna unguiculata (L.) Walp) renders the breeding task very complex. Therefore, a number of studies was carried out from 2006 to 2009 in field, pot and ‘’in-vitro’’ to identify new sources of resistance to three prevailing Striga races, SR 1, SR 5 and a newly occurring Striga race named SR Kp and to understand the genetic pattern of the underlying resistance of cowpea germplasm to Striga races found in Burkina Faso. To achieve these objectives, the following investigations were initiated: (i) a participatory rural appraisal (PRA), a participatory variety selection (PVS) and grain quality survey were implemented to identify cowpea breeding priorities for Burkina Faso Striga hot-spots; (ii) the identification of sources of resistance in Burkina Faso germplasm, using three prevailing Striga races of S. gesnerioides as sources of inoculum; (iii) the identification of the mechanisms of resistance underlying the resistance to Striga in such genotypes; (iv) a study of combining abilities of selected parents through a diallel cross; (v) a study of the segregation patterns in crosses involving resistant and susceptible sources and a study of the allelic relationships between different resistance sources. The participatory studies conducted in 2007 and 2008 over three districts in Striga hotspots; there was no effective control method against Striga at farmers’ level. These investigations highlighted the importance of cowpea across all sites. Rain decline over time, low input use coupled with a poor extension system were the major constraints mentioned by farmers. Differential reactions of genotype KVx61-1 for Striga resistance suggested that different Striga races were prevailing in different areas. Farmers’ preferred traits in cowpea genotypes were oriented towards grain quality such as big sized grain, white seed colour and rough texture of cowpea grain, except in Northern-Burkina Faso, where farmers preferred brown-coloured grain for food. Cowpea was also seen as an income generating crop. An evaluation of 108 genotypes was done in 2007 in the field (rainy season) and in pots (off-season) for Striga resistance assessments. The screening trials enabled the identification of sources of resistance to S. gesnerioides. Genotypes KVx771-10, IT93K- 693-2, KVx775-33-2, Melakh and IT81D-994 are potential sources of resistance to all three Striga races with acceptable yield. Landraces were susceptible and late-maturing whilst most wild species were resistant but with unwanted shattering traits. A combining ability study for Striga resistance parameters conducted in pots and a resistance mechanism study conducted ‘’in-vitro’’ were performed using F1 populations from a 10 x 10 diallel cross. The general combining ability (GCA) effects were significant for the resistance parameters Striga emergence date (DSE), Striga height above soil (SH), cowpea grain weight (CGW), hundred grain weight (HGW) for all Striga races involved and Striga vigour (SVIG) for SR 5 and SR Kp. The pot-screening showed that, regardless of the SR used as inoculum, the additive genes were important in conferring Striga resistance for parameters DSE, SH, CGW and HGW. The selection of parents could therefore result in breeding advance. Complete dominance, partial, over-dominance and non-allelic interactions (epistasis or failure of some assumptions) were present for some parameters. The ‘’in-vitro’’ screening showed that additive genes were important, with high narrow sense heritability values for the resistance mechanisms Striga seed germination frequency (GR) for SR 1 and SR Kp, the frequency of Striga radicle necrosis before the penetration in cowpea rootlet (NBP) for SR 5, the frequency of Striga radicle necrosis after the penetration in cowpea rootlet (NAP) for SR 1 and SR Kp and the susceptibility ‘’in-vitro’’ (SIV) for SR 5 and SR Kp. The selection of parents can be useful in accumulating the genes for Striga resistance mechanisms in progenies. The F2 populations derived from crosses between Striga-resistant x susceptible genotypes were evaluated in Striga infested benches in 2008 and 2009. The segregation patterns suggest that single dominant genes govern Striga resistance. The test for allelism showed that two non-allelic genes were responsible for the resistance to S. gesnerioides in cowpea. A new Striga resistance gene seems to be involved in genotype KVx771-10 resistance to S. gesnerioides, which confers resistance to all studied Striga races. Gene 994-Rsg in genotype IT81D-994 which confers Striga resistance to SR 1 and gene Rsg 3 also conferring Striga resistance to SR 1 segregated differently for the resistance to SR 5 suggesting that they were different but both confer resistance to SR 5.
Hormonal regulation of tuberization of cassava (Manihot esculenta Crantz)
(1984) Melis, Robertus Johannes Maria.; Van Staden, Johannes.
The relative distribution of dry matter over shoot and tuberous roots is an important factor in determining the yield of cassava. Under sub-tropical conditions the dry matter distribution pattern is not always efficient. During the summer the vegetative growth is generally excessive due to long days and high temperatures. Furthermore, it was found that a reduction of tuberous root mass occurs shortly after the winter period when the new canopy is formed. The role of endogenous hormones, in particular abscisic acid and cytokinins, in dry matter distribution and tuberization was studied. Furthermore, experiments were conducted on the effect of exogenous applied plant growth regulators on the growth of cassava. Inhibitor activity present in plant extracts, was tentatively identified as cis-abscisic acid. A high level of inhibitor activity, co-eluting with abscisic acid, was found throughout the tuberous roots. The highest level of inhibitor activity was detected under conditions which caused a high rate of tuberous root growth, ego with a low level of nitrogen fertilization. Gibberellic acid application to the leaves promoted shoot growth and led to a decrease in inhibitor activity of the tuberous roots. Shoot removal, however, stopped tuberous root growth without leading to changes in inhibitor activity. No clear correlation was found between inhibitor activity of tuberous roots and the rate of tuberous root growth of plants harvested from the field tentatively identified as the major cytokinins in tuberous root extracts. Cytokinin activity was concentrated in the meristematic region of the xylem. The level of cytokinin activity in the roots was much higher than in primary roots of the same plants. Gibberellic acid application to the leaves and shoot removal resulted in a reduction of the cytokinin level of tuberous roots. The nitrogen application to the plants had no clear effect on the cytokinin levels. In field-grown plants the highest level of cytokinin activity was found shortly after tuber initiation. Applications of Alar caused satisfactory reduction of shoot growth of young cassava plants grown in the greenhouse. The internodes were shortened, the leaf area generally reduced, while a relatively larger part of the dry matter was allocated to storage roots. The effect of Alar was further studied in field experiments. A growth analysis showed that a reduction of tuberous root mass occured shortly after the winter period, in September. Later in the second growing season, shoot and tuberous root mass increased at a relatively constant rate. Alar application (up to 4,5 grammes per Iitre) early in the second season failed to bring about major changes in dry matter distribution. Shoot removal at the end of the winter period was followed by excessive vegetative growth. Alar application reduced the internode length but the reduction of shoot growth was insufficient to cause a significant increase in yield. A nitrogen topdressing at the start of the second season increased the vegetative growth. However, Alar application, later in the season, did not inhibit shoot growth at any of the nitrogen levels applied. RSW 0411 which caused good reduction of shoot growth in the greenhouse, was not effective in the field.