The inbred lines of cucumber (Cucumis sativus L.) TX300, TX301, TX303 and TX306 (susceptible to downy mildew) were crossed separately as female parents (P1 ) with TX302 (resistant to downy mildew) as male parent (P2 ). Some characters of growth and yield components in relation to resistance to downy mildew in plant populations of the parents, F1, F2 and backcrosses to both parents were evaluated.
Results indicated that two pairs of dominant and recessive interaction genes controlled resistance to downy mildew disease. Susceptibility was dominant over resistance and the resistant dominant gene “R” expressed itself only in the presence of the recessive gene “s”. Leaf area, number of days from planting to the first male or female flower anthesis, yield/plant, sex ratio and set percentage were found to be inherited quantitatively. The nature of dominance for some components of resistance to downy mildew disease of cucumber caused by Pseudoperonospora cubensis (Berk and Curtis) Rostovzen ranged from partial dominance to over dominance in the different cross. Evaluating resistance by different criteria showed that, the broad and narrow sense heritability for resistance ranged from low to above intermediate and high in the different crosses.
The leaves of resistant male parent (TX302) contained higher phenols (free, conjugated and total phenols) and lower sugars (reducing, non-reducing and total sugars) contents than any of the susceptible female parents (TX300, TX301, TX303 and TX306). Highly significant positive correlation was detected between disease resistance and each of leaf area, number of days from planting to the first female flower anthesis and sex ratio. Meanwhile, it was negatively correlated with both fruit weight and yield/plant. Highly significant correlation was also detected between yield/plant and each of leaf area, number of days from planting to the first male or female flower anthesis, disease resistance, sex ratio and set percentage
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