Browsing by Author "Ndou, Vuledzani Nico."

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Chemical mutagenesis of wheat for herbicide resistance.
(2012) Ndou, Vuledzani Nico.; Shimelis, Hussein Ali.; Odindo, Alfred Oduor.
Weed infestation is one of the yield limiting factors in crop production. Weeds have negative effect on crop growth and productivity due to competition, allelopathy or hosting other harmful organisms. For large-scale wheat production, the use of wide spectrum pre-emergence or post-emergence herbicides remains the most valuable weed control tool. In South Africa, annual grass weeds are a major wheat production constraint, which is usually managed through application of pre-emergence herbicides. Due to limited water availability and low soil moisture content, these herbicides can often become ineffective and result into high weed infestations, which then have to be managed by manual cultivation or post-emergence herbicidal applications. However, there are no effective selective post-emergence herbicides available to control grass weeds in wheat. There is also limited option to use broad-spectrum post-emergent herbicides because they non-selectively kill the crop and weeds. Consequently, the use of herbicide resistant crops is a viable weed management system in wheat production. Breeding herbicide resistant crop varieties would allow farmers to safely use post-emergence herbicides without damaging the crop. Subsequently yield and quality losses will be reduced significantly. Thus, the development of herbicide resistant crop varieties through mutation breeding is a novel approach for effective weed management under both small-scale and commercial farmers. Mutagenesis has been recognized as one of the most efficient method to induce genetic variation in plants. Through induced mutations, development of new variants is possible that could be manipulated in plant breeding programs. Mutation leads to alteration of various traits in crop plants including plant height, improved nutritional quality, shorter growing period, increased tolerance or resistance to abiotic and biotic stresses. Ethylmethanesulphonate (EMS) is one of the most widely used chemical mutagens to induce mutagenesis in crop plants. The objectives of this study were to: 1) determine the optimum EMS concentration, treatment temperature and duration that would provide desired germination percentage and vigorous and healthy seedlings for effective mutagenesis in wheat, 2) investigate variations in agro-morphological traits in two selected wheat varieties (SST56 and SST875) after EMS mutagenesis and 3) select herbicide resistant wheat germplasm after inducing genetic variation using EMS using two selected wheat varieties (SST56 and SST875). The objectives were achieved through three independent studies as outlined below: In the first study seeds of four selected wheat varieties (B936, B966, SST387 and SST875) were treated in two replicates with three EMS concentrations (0.3, 0.5, and 0.7%), three temperature regimes (30, 32.5 and 35 °C) at four time durations (0.5, 1, 1.5 and 2 hrs). Results showed highly significant interactions (P<0.01) among varieties, EMS concentrations, temperature and exposure time on seedling emergence, germination and seedling height. Seeds treated with the highest EMS dose (0.7%), temperature (35ºC) and long exposure time (2 hr) showed delayed emergence by 18 days. At 30ºC, 0.5hr and 0.3% EMS varieties B936, B966 and SST875 had early emergence (6 days). B936 and SST387 had 50% while B966 and SST875 had 53% and 57% germination, respectively. These results were observed at EMS level of 0.7%, 300C and 1.5 hr exposure time in B936 and EMS at 0.5%, 350C and 1.5 hr in B966. SST387 and SST875 required EMS dose at 0.5%, 32.50C and 2 hr treatment time. Other low or high treatment combinations were invariably ineffective comparedto untreated control. During the second study two selected varieties (SST56 and SST875) were subjected to EMS mutagenesis using 0.5% v/v EMS at 32.5oC for 1 hr. Field trials were carried out at Ukulinga research farm of the University of KwaZulu-Natal in the randomized complete block design with two replicates. Data on nine important agro-morphological traits were collected and analyzed using the analysis of variance (ANOVA), correlation and principal component analysis (PCA) procedures. Significant variations were found among the agro-morphological traits between M1 individuals compared to untreated checks. The mutagenesis significantly reduced seed germination in the field at 40% in both varieties. The treatment significantly delayed days to heading by 8 days and shortened days to maturity by 13 days in both varieties. EMS treatment also significantly reduced plant height at 18 cm in SST56 and 21 cm in SST875 and spike length reduced by ~2.5 cm in both varieties. Plant height had positive and significant correlation with number of tillers, number of seeds per spike, flag leaf length and 100 seed weight. However, it had negative correlation with the number of days to maturity. The PCA revealed that three principal components (PC1, PC2 and PC3) accounted to 57% of the total variations among the agro-morphological traits in both varieties. PC1 alone contributed to 27.7% of the variation which was well-correlated with plant height (0.767), tiller number (0.812), number of seeds per spike (0.599) and seed yield (0.720). PC2 explained 15.6% of the variation and well-correlated with germination percentage (0.784), spike length (0.554) and flag leaf length (0.772). PC3 accounted to 12.4% of the variation and had negative correlation with days to maturity (-0.730). In the last study, seeds of two selected wheat varieties (SST56 and SST875) were treated with EMS at 0.5% concentration for 2 hr at 32.5ºC. Treated seeds and comparative controls were planted at the experimental farm of the University of KwaZulu-Natal using the randomized complete block design. Four weeks after planting M1 plants and untreated standard checks were sprayed with two herbicides, i.e. metsulfuron-methyl and bromoxynil at three different doses viz. 2x, 4x and 8x above the recommended rate of 4 g ha-1 and 2 kg ha-1, respectively. Two weeks after the treatment herbicide resistance were assessed. Results showed significant difference among varieties, tested herbicides and doses used. The EMS treated wheat lines showed variable degree of herbicide resistance compared to untreated controls. Overall, the study established the requirement of variety specific EMS dose and treatment temperature and duration that could be used for inducing large-scale mutation to select targeted mutant individuals in wheat. Further, the study found that EMS has the potential to increase agro-morphological variations in wheat to select useful and novel mutants with desired phenotypic traits and herbicide resistance which will be subjected for further selections to identify stable and herbicide resistance lines.
Genetic analysis of maize hybrids derived from temperate by tropical germplasm under low and high plant population density stress.
(2016) Ndou, Vuledzani Nico.; Derera, John.; Gasura, Edmore.
Maize is a major staple food crop in Sub-Saharan Africa and it plays a vital role in the livelihoods of small-scale and resource-limited farmers. The demand for maize is high and is also expected to increase due to the increasing population. Grain yield per unit area can be increased by increasing the plant population density. In this regard, the new improved maize varieties should be richly endowed with high and enhanced frequency of genes that confers high yield under varying plant population density stress conditions. The objective of this study was to conduct a genetic analysis of maize hybrids derived from temperate by tropical germplasm under low and high plant population density stress in order to identify hybrids that combine high yield, earliness and tolerance to high plant population density stress as well as the breeding strategy for these essential traits. New maize inbred lines derived from tropical by temperate populations were selected based on observation trials for yield potential and prolificacy to ensure adaptation. These were used to generate hybrids using two different testers with different genetic attributes. The hybrids were planted in four environments; Ukulinga1 (Env-1), Cedara (Env-2), Dundee (Env-4) and Ukulinga 2 (Env-3) in two replications. One of these environments (Ukulinga 2), had a high plant population density. Data was collected on various agronomic traits that include grain yield, plant height, ear height, days to anthesis, ear position, number of ears per plant, anthesis-silking interval, grain moisture content, root and stem lodging, number of tassel branches, number of leaves above the cob, days to cob dryness and number of plants per row. Analysis of variance for single sites showed that hybrids were significantly different on the traits studied, and across environments (low and high plant population densities). This enabled the genotype plus genotype by environment biplots to be used in identifying varieties suitable for given environments as well as stable and high yielding varieties. The line by tester analysis of variance showed that the general combining ability effects of the lines were significant (P<0.05) and that narrow sense heritability was low for grain yield but higher for other traits. The results of this study identified hybrids (and their inbred lines) that performed better under high plant population density stress and the traits associated with high yield under high and low plant population densities across different genetic backgrounds. Superior, stable and high yielding hybrids were selected and hybrids 15XH214, 15XH215 and 15XH121 were the most adaptable genotypes across environments, out-competing the highest yielding commercial hybrids such as PAN6Q345BC and BG5285 under high stress conditions. With regards to the genetic gain, the study revealed 16.70 % and 22.70 % genetic gain of grain yield under both Tester 9 (Testers A) and DTAB32 (Tester B), respectively, which was displayed by the high-yielding experimental hybrids. The studies also revealed high genetic variability of traits among hybrids, which can be exploited to obtain further breeding gains. The high genetic gains and stress tolerance indices of these hybrids over the checks were related to resistance to stem lodging and increased ears per plant. Most of these hybrids were derived from the tester DTAB32 which is associated with a huge contribution to stress resistance, including lodging. Based on the combining ability analysis, inbred lines with resistance to stem lodging and high ear prolificacy were identified as, 15XH214 and 15XH215 under tester B and 15XH121 under tester A. In producing better hybrids, such inbred lines were complimented by Tester DTAB32 that has been shown to have resistance to lodging and other abiotic stresses. The identification of the best genotypes based on the increase of plant population density stress tolerance was achieved through the selection of the hybrids which possessed good standability, yield stability and high grain yielding ability. The genetic coefficient of variation (GCV) and narrow sense heritability values estimated were moderate for all traits but low for grain yield thus calling for a need to identify the traits which could be targeted for improving the grain yield of the hybrids based on indirect selection of traits highly correlated with grain yield, easy to measure and have higher heritability. Generally, the results of this study identified inbred lines with good general combining ability (GCA). This shows the possibility of developing desirable cross combinations and synthetic varieties through crossing of inbred lines with desirable traits of interest. Furthermore, promising cross combinations identified in this study could be used for future breeding work as well as for direct release after confirming the stability of their performances observed in this study. Hence, the information on combining ability from this study may be useful for researchers to develop high yielding varieties of maize under high and low plant population densities as well as assisting in defining genetic advance; which will enable effective and efficient selection of the germplasm lines to produce new maize hybrids. From the study it was revealed that ears per plant and stem lodging were highly correlated with grain yield and had high positive direct effects on grain yield under high plant population density. These traits did not only have high correlations with grain yield, but also had high narrow sense heritabilities as well and were easy to select for, thus making them ideal candidates for indirect selection for improved grain yield under high plant population density stress. This study concluded that high plant population density reduces ears per plant and increases stem lodging which result in reduced grain yield. Development of ideal breeding strategies that can improve grain yield under high plant population density is desired. Advance testing of these maize hybrids in more seasons could enhance good and desired breeding productivity with reference to cultivar stability and adaptation across environments. This suggested that this selected hybrids exhibits progressive stability in different environments, which is a desirable attribute for the smallholder farming conditions, where management conditions are variable. These hybrids have the potential to respond positively to improved environmental conditions, since they were able to obtain high yields under high plant population density. Therefore, they can be recommended for advancement in the following season. Further tests on these experimental hybrids for commercial use could be done to enable their release given the need for increased maize production and productivity in South Africa, to prevent recurrent food shortages that result food insecurity.