Abstract
The present research includes characterization of sweet gourd accessions using morphological and molecular markers, genetic diversity study, interrelationships among yield components and combining ability study. The accessions exhibited wide range of variation on different morphological, yield and yield components. Among 81 accessions of sweet gourd, CM044, CM118 and CM120 performed better in respect of different yield components. In all the traits, genotypic coefficient of variation (GCV) was always smaller than phenotypic coefficient of variation (PCV). Narrow differences between GCV and PCV and high heritability coupled with high genetic advance confirmed least environmental effects on number of fruits and yield per plant, which offered better scope for selection. Based on multivariate analysis, the accessions were grouped into 8 clusters. There was no relationship between genetic divergence and geographical distribution of the accessions. Yield per plant had the maximum contribution towards total divergence. From the isozyme analysis, 12, 8 and 9 zymotypes were detected from peroxidase (PRX), glutamate oxaloacetate transminase (GOT) and malate dehydrogenase (MDH) isozymes, respectively. Zymotypes P1 (in case of PRX), G3 (in case of GOT) and M1 (in case of MDH) were found most frequent which covered 17.28, 25.93 and 40.74% of the total sweet gourd accessions, respectively. Using hierarchical clustering based on isozyme analysis, 81 accessions were grouped into 8 clusters. Genetic diversity of 81 accessions was analyzed using variation at 50 RAPD loci, of which 58% were polymorphic. The highest pair wise genetic distance (0.446) in RAPD analysis was recorded in between CM041 and CM092. The mean gene diversity among all the accessions was 0.184. The UPGMA dendrogram, based on Nei's genetic diversity demonstrated 8 clusters. Clustering of the accessions based on morphological characters did not match with the clustering obtained from isozyme and RAPD analysis. Studies on interrelationships among yield and yield components revealed that genetic correlation coefficient was higher than corresponding phenotypic ones for all the characters studied, thereby establishing strong inherent relationships among them. Path coefficient analysis showed that the number of fruits per plant had maximum direct effect on yield per plant followed by flesh thickness of fruits, both at genetic and phenotypic level. Success of crossing varied from 13.33 to 80% during diallel crosses (without reciprocal) between selected eight genotypes. All the crossing combinations showed hybrid vigour in respect of yield per plant and per hectare over respective parents. The mean square values for combining ability analysis showed that both general combining ability (GCA) and specific combining ability (SCA) were highly significant for all the characters studied, indicating that additive and non-additive genetic components were responsible for expression of those characters. Parents CM026, CM044 and CM122 were good general combiners for almost all the important characters. Estimates on specific combining ability (SCA) and heterosis in F1 generation showed that there were a good number of crosses having significantly positive and expected negative effects for different important characters of sweet gourd, indicating the possibilities of exploiting these crosses or these crosses may be used in the development of hybrid varieties. Three isozyme systems viz. PRX, GOT and MDH were used to identify the F1 hybrids from their parents, where hybrid specific bands at new loci were observed. Considering all the enzyme systems, half of the hybrids showed more affinity with their female parents and half of them were with male parents.