Development of tropical gynoecious lines in cucumber (Cucumis sativus L.)

Abstract

The present study ‘Development of tropical gynoecious lines in (Cucumber sativus L.) was carried out at Department of Olericulture, College of Horticulture, Kerala Agricultural university, Vellanikkara, Thrissur during August - November 2014 and February - May 2015 to evaluate the F1 hybrids and their F2 population for identifying stable tropical gynoecious lines of salad cucumber. Twelve hybrids produced by crossing gynoecious line EC 709119 with selected tropical monoecious parents were evaluated for gynoecy under rainshelter. Observations on important quantitative and qualitative characters were recorded. These hybrids were selfed to generate F2 population. F2 population was evaluated for expression of gynoecious character, viz., days taken for female flower anthesis, node at which first female flower emerged and total number of female flowers. The data was subjected to analysis of variance and variability among the genotypes was calculated. Most of the characters exhibited high heritability except for fruit parameters like fruit length, fruit girth and flesh thickness. For gynoecy F2 population from the cross EC 709119 x IC 538186 was observed as the most promising one. This population took only minimum days to form female flower and took minimum number of nodes to form female flower with highest number of female flowers and minimum male flowers. Sex ratio was estimated for parents, F1 hybrids and F2 population. Some of the parents having high sex ratio failed to transmit the same to its hybrid progenies. Among the parents, IC 538186 exhibited highest sex ratio. The highest sex ratio among the F2 population was for EC 709119 x IC 538186. Two populations viz., EC 709119 x IC 527427 and EC 709119 X IC 538186 exhibited a sex ratio of more than 2. The 4 F2 population evaluated for gynoecious trait were classified into monoecious and gynoecious character and tested for goodness of fit based on chi square test with monohybrid ratio of 3:1 being monoecy dominant over gynoecy. Out of the 4 populations, 2 populations were found to express significant value and fit in 3:1 ratio for dominant monoecious trait. The other 2 populations failed to fit in the 3:1 ratio. Bitterness was an important quality character which was absent in most of the parents except three of them during initial harvest. The crosses involving parents prone to bitterness were found to be bitter during later harvest, though all crosses were free of bitterness during initial stage. During later harvests, five parents were found to be bitter. Downy mildew incidence on parents and F1 hybrids were analyzed and Percentage of Disease Intensity (PDI) was estimated. Among parents, IC 538186 exhibited minimum infection and falls under the category of moderate resistance. Hybrid, EC 709119 x IC 538186 exhibited minimum infection and falls under the category of moderate resistance. Among 12 F2 populations, EC 709119 x IC 538186 produced maximum number of true gynoecious plants whereas eight F2 populations failed to produce even one true gynoecious plant. This population also exhibited moderate resistance against downy mildew disease and could be selected for developing true breeding stable gynoecious line for future breeding programme. Present investigation proved the scope of developing tropical gynoecious line from temperate lines by crossing with potential-monoecious lines and making selection in advance segregating generations for gynoecy.