GENE EFFECTS FOR RESISTANCE TO GROUNDNUT ROSSETTE DISEASE IN EXOTIC VALENCIA GROUNDNUTS

Two exotic Valencia groundnut (Arachis hypogaea L.) breeding lines (NuMex-M3 and Valencia C) with superior characteristics were introduced by National Legume Improvement Program at the National Semi- Arid Resources Research Institute (NaSARRI), from the United States of America, to broaden the Valencia germplasm base in Uganda. The materials were evaluated for biotic and abiotic stresses, but succumbed to groundnut rosette disease (GRD). For these superior lines to find utility in Uganda, they need further improvement by introducing resistance genes to GRD. A study was conducted at NaSARRI to determine nature of gene action controlling resistance to GRD, using the Exotic Valencia groundnut breeding materials.Six generations that included F_1, F_2, BC-1P-1 and BC-1P-2 populations, together with their parents (P-1and P-2) of each of the six crosses, namely Valencia C (P-1) × ICGV-SM 90704 (P-2), Valencia C (P-1) × ICGV-SM 96801(P-2), Valencia C (P-1) × ICGV-SM 99566 (P-2), NuMex-M3 (P-1) × ICGV-SM 90704 (P-2), NuMex-M-3 × ICGV-SM 96801 (P-2), and NuMex-M-3 (P-1) × ICGVSM 99566 (P-2), were evaluated for GRD resistance.The study reaveled additive and non-additive gene effects in the control of GRD resistance.Three types of epistatic gene effects, viz. additive × additive [i], additive × dominance [j] and dominance × dominance [l],were exhibited tocontrol GRD resistance. The component dominance × dominance [l] was more predominant in Valencia C × ICGV-SM 96801, NuMex-M-3× ICGV-SM 96801, NuMex- M-3× ICGV-SM 90704, NuMex-M-3 × ICGV-SM 99566 and Valencia C × ICGV-SM 99566 crosses. Opposite and significant signs of dominance [d] and dominance × dominance [l] components indicated the importance of duplicate epitasis in the latter crosses in the control of GRD resistance, which revealed a complex nature of inheritance of GRD resistance.