Generation mean analysis of resistance to downy mildew in adult muskmelon plants

Abstract

Abstract Downy mildew (Pseudoperonospora cub ensis) is the most devastating disease in muskmelon (Cucumis melo). A generation mean analysis study was designed to determine the types of gene action and estimate the heritability for resistance to downy mildew in four selected crosses of muskmelon. Generation mean analysis revealed that genetic dominance may be of greater importance for expres sion of resistance to downy mildew in both green house and field experiments and in all the crosses. The F1 mean was significantly lesser than the mid parent value and skewed towards resistant parent in all the crosses. Negative sign associated with gene effects indicated, in those crosses, that disease level could be decreased in relation to midparent. All the crosses expressed significant and positive additive (d) gene effects. Dominance (h) and dominance 9 dom inance (l) gene effects had opposite sign in all crosses and both experiments, which implied duplicate type of gene action. High mid-parent heterosis in all the crosses indicated strong dominance effects (as combi nation of parental alleles) for resistance to downy mildew. In all the crosses, both resistant and suscep tible parent contributed one or more dominant/partially dominant factors for resistance. Estimates of broad sense heritability were high and relatively consistent in both experiments. The two different screening exper iments showed that fixable gene effects (d ? i) were lower than the non-fixable gene effects (h ? l) in all the crosses indicating greater role of non-additive effects in the inheritance of resistance to downy mildew. Resistance to downy appeared to be controlled mainly by dominance effects, therefore the inbred lines IIHR 121 and IIHR 122 could be used strategically to exploit heterotic effects.