Response of progeny from the cross Cucurbita moschata X C. ecuadorensis to infection with papaya ringspot virus type W and watermelon mosaic virus type 2

Abstract

C. moschata cv. Butternut was compared with 11 selected lines produced through 3 backcrosses from cv. Butternut X C. ecuadorensis. The comparisons involved pruned or not, and naturally infected or mechanically inoculated with papaya ringspot (type W) potyvirus (PRV-W) plus watermelon mosaic II potyvirus (WMIIV). The objectives were to determine suitable evaluation procedures and the extent of genetic variation for resistance in the populations. All plants expressed moderately severe leaf symptoms which were only poorly correlated with fruit symptoms (r = 0.46) and yield (r = -0.56). Fruit distortion, which was greatest on manually inoculated and on pruned plants, differed among genotypes being highest in cv. Butternut. Fruit number was highest (5.5) on naturally infected, unpruned plants and lowest (3.3) on mechanically inoculated, pruned plants. The effects of pruning and method of inoculation on yield varied with genotype. Estimates of broad sense heritability on a plot mean basis were high (0.8) for yield and moderate (0.4) for fruit symptoms. It was concluded that sufficient variation existed to improve yield and reduce severity of fruit symptoms but not to decrease leaf symptoms. In the population studied, yield and severity of fruit symptoms on manually early-inoculated, unpruned plants should be the basis of selection.