Abstract:

Groundnut rosette disease (GRD) is the most destructive virus disease of Valencia groundnuts (Arachis hypogaea L.) in Africa. To widen the germplasm base of Valencia types grown in Uganda, two exotic Valencia lines namely, NuMex-M3 and Valencia C, were imported and evaluated for GRD by the Groundnut Improvement Program of National Semi-Arid Resources Research Institute (NaSARRl) but they succumbed to the disease. Sources of GRD resistance were found in Spanish and Virginia types, which could complicate genetic improvement of Valencia type of groundnuts due to lack of information on the genetics of GRD resistance on the available breeding lines. This study was conducted (i) To determine heritability for resistance to GRD in Valencia groundnuts ii) To determine gene action controlling resistance to GRD in Valencia groundnuts and iii) To evaluate F2 and backcross segregating populations for recovery of Valencia type characteristics . Six crosses were made between; Valencia C (P|) x ICGV-SM90704 (P2), Valencia C (P,) NuMex-M3 (Pi) x ICGV-SM 96801(P2), Valencia C (P,) x x ICGV-SM 90704 (P2), NuMex-M3 x ICGV-SM 99566 (P2), ICGV-SM 96801 (P2), and NuMex-M3 (Pi) x ICGV-SM 99566 (P2), to generate Fi, F2, BC,P| and BC,P2 populations. The parents (Piand P2) together with F|, F2, BC|Pi and BC|P2 populations of each cross were evaluated in Randomised Complete Block Design (RCBD). Data on GRD severity were collected on a 1-9 score scale. Phenotypic Coefficient of Variation (PCV), Genotypic Coefficient of Variation (GCV), Genetic Advance as percent of Mean (GAM) and heritability were estimated using variance components. Scaling tests were performed to determine the type of gene effects controlling GRD resistance. Cluster analysis was performed using data on morphological descriptors and similarity coefficients were generated between Valencia lines and their respective segregating populations. The PCV and GCV estimates were high (20.04-70.1%) in all the six crosses except for Valencia C x ICGV-SM 96801(18.1%) and NuMex-M3 x ICGV-SM 96801(17.1%) which exhibited moderate GCV values. Broad and narrow sense heritability estimates for GRD disease score ranged from (64.1 to 73.7%) and (31 to 41.9%) respectively in all the crosses. The GAM was high in all the crosses (21-50.7%) except for Valencia C x ICGV SM 96801 (14.67), M3 x ICGV-SM 99566 (18%) and NuMex-M3 x ICGV-SM 96801 (13.5%) crosses that exhibited moderate GAM.