Genetic analysis and improvement of groundnut (Arachis hypgaea L.) for drought tolerance and seed yield in Malawi.
Sultan, Masoud Salehe.
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Groundnut (Arachis hypogaea L,) is one of the major sources of food and income for smallholder farmers in Malawi. It is a valuable food security crop that supplies fats and proteins to the predominantly maize–based Malawian diet. Although, groundnut production is a profitable venture for smallholder farmers in Malawi, its productivity is low averaging 250 – 800 kg/ha as compared to a yield of about 4.0 t/ha obtained at research stations. The decline in productivity of groundnuts is due to several abiotic and biotic constraints that smallholder farmers encounter, among them drought due to inadequate and highly variable rainfall in the country. Information on response of different genotypes to drought stress and the explanation of these variabilities is an important requirement in breeding for drought tolerance improvement in groundnut. The main objectives of the study were: (i) to determine the effect of drought stress on the growth performance of groundnut genotypes with respect to morpho-physiological traits,(ii) to identify the relevant traits related to drought tolerance and their relationship to seed yield under drought stress conditions, (iii) to estimate the relative importance of additive and non-additive gene action in controlling the inheritance of drought tolerance traits under moisture stressed conditions and (iv) to investigate the genetic variation existing among genotypes in relation to morpho-physiological traits related to drought tolerance. Twenty-five genotypes from the International Crops Research Institute for Semi-Arid Tropics (ICRISAT) Malawi were evaluated during 2016/17 under rainfed field condition at the drought-testing site of Ngabu Agricultural Research Station. The results indicated high genotypic coefficient of variation (GCV) coupled with high genetic advance (GA), genetic advance as percent of mean (GAM) and heritability estimates for days to maturity (DM), seed yield (SY), relative water content (RWC), biomass (BM), number of filled pods (FP) and pod yield (PY). Seed yield was highly significant and positively correlated with shelling percentage (SHP), hundred seed weight (HSW), SPAD chlorophyll meter reading (SCMR), days to maturity (DM), biomass (BM), relative water content (RWC) and harvest index (HI). Furthermore, path analysis showed that harvest index, biomass, pod yield, shelling percentage, SPAD chlorophyll meter reading, relative water content and days to maturity had the highest direct and indirect effects on seed yield. General combining ability effects were significant for almost all studied traits indicating the importance of additive gene action. Specific combining ability effects were also significant for days to maturity, seed yield, biomass, harvest index, number of field pod and pod yield indicating importance of non-additive gene action controlling the inheritance of these traits. This suggests that both additive and non-additive gene action were important in controlling the majority of the traits. However, additive gene action was more predominant for all traits studied as it was evidenced by its significant (P<0.05) positive GCA effects coupled with high variance components as compared to its interactions. This also, was supported by a high Baker’s ratio of close to unity (X>0.5) ranging from 0.78 to 0.96 for all measured traits. Among male parents, ICGV-SM 02724 and ICGV-SM 94139 were identified as good combiners, whereas among females, CG 7 and ICGV-SM 01721 were good combiners. These parents have outstanding breeding value as proven by their high and significant GCA effects. The crosses Pendo x Akwa, ICGV-SM 99555 x ICGV-SM 02724, ICGV – SM 99551 x Baka and ICGV-SM 01721 x ICGV-SM 94139 had significant SCA effects for seed yield, number of filled pod, harvest index and pod yield. The cross, Pendo x ICGV-SM 02724 was identified as potentially useful for developing early maturing varieties. These crosses could be used for further selection in breeding programmes for developing drought tolerant cultivars. Genotypes also showed different degrees of tolerance where seven genotypes with high yield, favourable adaptive traits and useful for breeding were selected. The principal component analysis under moisture stressed condition also showed that specific leaf area, days to maturity, biomass, number of filled pod, hundred seed weight and pod yield had more influence during selection. Based on the current results, breeding for drought tolerance for the material studied will be possible by focussing on relative water content, shelling percentage, number of filled pod, SPAD chlorophyll meter reading, pod yield and hundred seed weight as selection criteria, accompanied with extensive evaluation of the material under multi-located trials.