YIELD PENALTY ASSOCIATED WITH STACKING RESISTANCE TO LATE LEAF SPOT, ROSETTE DISEASES AND DROUGHT STRESS IN GROUNDNUT (ARACHIS HYPOGAEA L.)

Groundnut production is constrained by late leaf spot, groundnut rosette disease and drought which are responsible for up to 100% yield loss. This study was conducted to determine yield penalty associated with stacking resistance to late leaf spot, rosette and drought stress in groundnut genotypes. Twenty eight genotypes comprising single, double and multiple resistances for the diseases and tolerant to drought were evaluated in screen houses at Namulonge and Kabanyolo, in 2017. Completely randomized design was used in two replications. Three watering regimes were applied. Diseases severity was scored at harvest based on 1-9 scale. Drought was assessed with relative water content and leaf membrane stability index. Yield penalty was calculated as yield of the resistant genotype under optimum conditions minus yield of the same genotype under stress. The results of analysis of variance showed significant difference (P < 0.001) from one location to another and genotype-by-location effect was significant for most traits. The highest pod yield was observed at optimum conditions and under disease control, while the lowest was observed under the combination of diseases and drought. The highest yield penalty (19.98) was recorded by rosette resistant genotype SGV 0007. Low yield penalty (6.6), due to leaf spot and rosette diseases, was observed for genotype Abutalata. Penalty was positively correlated (r = 0.24) with relative water content and rosette and negatively correlated with leaf spot. Genotypes which showed low yield penalty could be valuable genetic materials for breeding of groundnut resistance to multiple stresses in Uganda or similar environments.