HETEROSIS, COMBINING ABILITY AND GENE ACTION IN WATERMELON (Citrullus lanatus (Thunb.) Mansf.)
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Date
2012-06
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jau,junagadh
Abstract
The present investigation was undertaken in watermelon in order to estimate heterosis, combining ability and nature of gene action involved in the inheritance of fruit yield and its components characters, viz., days to open first female flower, days to first picking, number of primary branches per vine, length of main vine (m), number of fruits per plant, average fruit weight (kg), fruit yield per plant (kg), flesh weight (g), fruit rind weight (g), flesh to rind weight ratio, number of seeds per fruit, 100-seed weight, fruit diameter (cm), total soluble solids (TSS). The crosses were attempted by adopting diallel analysis (excluding reciprocals) involving eight elite genotypes during summer-2011. The resultant 28 hybrids along with their parents were evaluated in randomized block design with three replications during rabi/summer-2011-12 at Instructional Farm, College of Agriculture, Junagadh Agricultural University, Junagadh.
The analysis of variance for experimental design revealed highly significant mean squares differences due to genotypes for all the characters, indicating sufficient amount of genetic variability for the fourteen traits studied. The magnitude of heterotic effects was high for fruit yield per plant, average fruit weight, length of main vine and flesh weight, low to moderate for days to open first female flower, days to first picking, number of primary branches per vine, number of fruits per plant, flesh to rind weight ratio, number of seeds per fruit and total soluble solids (TSS). The high, significant and positive standard heterosis for fruit yield per plant and some of its component traits were recorded in the crosses, GP-42 x GP-42 (b), RW-187-2 x GP-42, RW-187-2 x Sonam, GP-10 (b) x RW-187-2 and RW-187-2 x GP-42 (b).
The general and specific combining ability variances were highly significant for all the characters which indicated that both additive and non-additive type of gene effects played a vital role in the inheritance of all these traits. However, the SCA variance component was higher in magnitude than respective GCA variance for all the characters except for total soluble solids (TSS), suggested greater role of non-aditive genetic effects in the inheritance of these characters. The potence ratio less than unity confirmed the preponderance of non-aditive gene action for all the traits studied and emphasized the utility of hybrid breeding approach to exploit existing heterosis in the watermelon.
The estimate of GCA effects indicated that parents GP-10 (b), RW-187-2, GP-42 and GP-42 (b) were good general combiners for fruit yield per plant and some of its component traits. The parents, Durgapura Lal, RW-187-2 and Sonam were found to be good combiners for earliness. Considerable harmony was observed between per se performance of parents and their GCA effects for fruit yield and most of its traits.
Crosses showing high SCA effects for fruit yield also depicted high SCA effects for one or more of its yield components. The cross RW-187-2 x Sonam had high SCA for fruit yield per plant due to good x poor general combiner parents. The cross displaying high SCA effects did not always involve parents with high GCA effects.
Estimation of variance components of D, H1 and H2 revealed that additive as well as dominance gene effects were involved in the inheritance of most of the traits studied with preponderance of non-additive gene action for all the traits except days to open first female flower and total soluble solids. These findings were also confirmed by estimates of GCA / SCA variance component ratio.
Average degree of dominance revealed over dominance for all the traits except complete dominance for days to open first female flower and partial dominance for total soluble solids. Asymmetrical distribution of positive and negative genes in the parents was observed for all the traits. Narrow sense heritability was found to be more than 50 per cent for all the traits (except days to first picking and length of main vine).
The overall results of present investigation suggested that reciprocal recurrent selection procedure would mop up the additive gene effects and would also allow dissiparation of non-additive gene effects. Biparental mating may also be used in the segregating generations to break the undesirable linkages and to exploit both additive and non-additive gene effects simultaneously for isolating superior transgressive segregants in later segregating generations. Due to preponderance of non-additive gene effects of fruit yield and most of its component traits, heterosis breeding would also be practically feasible in watermelon.
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plant breeding