Inheritance of late leaf spot (phaeoisariopsis personata) resistance in valencia groundnuts
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Late leaf spot (LLS) Phaeoisariopsis personata (Berk. and Curtis) Deighton is one of the most important foliar diseases of groundnut worldwide. Although fungicide treatment is effective, it is uneconomical to use because of high cost. The deployment of resistant cultivars is a better option to control LLS disease in groundnut. The study was initiated to (i) determine heritability for LLS resistance and (ii) the type of gene action controlling LLS resistance. Breeding materials including F1, F2, and F1backcrosses to susceptible BC1P1 and resistant parents BC1P2 along with their respective parental lines of crosses between NuMex-M3× ICGV-SM 02501, Valencia C × ICGV-SM 02501, Valencia C × SGV-07009 and Redbeauty × ICGV-SM 03590 were evaluated in RCBD with three replications at the experimental field at National Semi-Arid Resources Research Institute (NaSARRI), Serere Uganda. Spreader row technique was used to maximize leaf spot inoculum pressure under natural conditions and late leaf spot severity was assessed using a modified nine point scale (1-9). Analysis of variance was performed for generations of each cross, phenotypic and genotypic coefficients of variability, and heritability were estimated using variance components. A joint scaling test was used to determine the nature and magnitude of gene effects controlling LLS resistance. It was observed that all the crosses had highly significant differences among generations for late leaf spot resistance. The Phenotypic coefficients of variability (PCV) estimates were high in NuMex-M3 × ICGV-SM 02501 (28.82%) and Valencia C × ICGV-SM 02501 (24.51%) crosses and moderate in Redbeauty × ICGV-SM 03590 (16.89%) cross. The genetic coefficient of variation (GCV) estimates were high in cross NuMex-M3 × ICGV-SM 02501 (23.13%), moderate in Valencia C × ICGV-SM 02501 (15.87%) and low in cross Redbeauty × ICGV-SM 03590 (9.50%). Broad-sense heritability estimates for LLS disease score were 32%, 37% and 64%, respectively, for Redbeauty × ICGV-SM 03590, Valencia C × ICGV-SM 02501 and NuMex-M3 × ICGV-SM 02501crosses. Narrow-sense heritability estimates were 12%, 27% and 36%, for Redbeauty × ICGV-SM 03590, Valencia C × ICGV-SM 02501 and NuMex-M3 × ICGV-SM 02501 crosses respectively while Genetic advance as percent of mean (GAM) were low in cross Redbeauty × ICGV-SM 03590 (4.17%), moderate in Valencia C × ICGV-SM 02501 (13.63%) and high in NuMex-M3 × ICGV-SM 02501 (21.37%). A simple additive- dominance model was adequate for the inheritance of resistance to LLS in NuMex-M3 × ICGV-SM 02501, Valencia C × ICGV-SM ix 02501and Redbeauty × ICGV-SM 03590 crosses. However, the additive effects were more important than dominance. Based on the observed results it can be concluded that selection for LLS resistance disease score is possible. However, the amount of variation and magnitude of gene effects depended on the genetic backgrounds of the materials used in the study. The best strategy for obtaining LLS resistant genotypes is selection of the disease score trait in initial inbreeding generations (F3 or F4) for the cross between NuMeX-M3× ICGV-SM 02501, followed by selection in the following generations with higher inbreeding levels in other crosses.