PhD

A study was undertaken at the College of Agriculture, Vellayani during 1990-91 aimed at inducing recombinations of the economic attributes of Bhindi (Abelmoschus esculentus (L.) Moench) and the yellow vein mosaic disease resistance of wild relatives. A preliminary evaluation of 56 accessions revealed good genetic diversity in Bhindi germplasm. The accessions were grouped into four clusters. The characterization of germplasm was done based on IBPGR descriptors. High genotypic coefficients of variation were exhibited by weight of fruits per plant, leaf area, height of plant, number of fruits per plant, single fruit weight and number of branches per plant indicating scope for selection. High heritability along with high genetic advance was recorded for weight of fruits per plant, height of plant, leaf area and number of seeds per fruit. Low heritability coupled with low genetic advance recorded for yellow vein mosaic disease incidence indicated the predominant role of environment in the inheritance of disease resistance.

Correlation studies revealed that number of leaves per plant, leaf area, number of branches per plant, fruit girth and single fruit weight could be considered as the major characters contributing to yield in Bhindi. Among the yield components, number of fruits per plant and single fruit weight recorded the maximum positive direct effects on yield. Number of branches per plant and single fruit weight recorded maximum positive and negative direct effects, respectively on yellow vein mosaic disease (YVMD). The selection of early flowering types with increased fruit weight is suggested for enhancing the level of YVMD resistance.

Varietal difference in compatibility of A. esculentus with the donor parents, A. caillei and A. tetraphyllus was noticed. Reciprocal crosses registered higher compatibility than the direct crosses. Natural crossing of A. tetraphyllus with A. esculentus and A. caillei also was observed.

The line x tester analysis with the three cultivated accessions as lines and the wild types as testers indicated the predominance of non-additive gene action for majority of the characters in interspecific hybrids. A. caillei (T1)was found to be the better general combiner for majority of the yield components and yellow vein mosaic resistance. Majority of the hybrids recorded negative heterosis for yield and its components. However, few hybrids manifested significant desirable heterosis for days to flowering, number of fruits per plant and fruit length. All the hybrids were completely free from YVMD like the donor parents.

High pollen sterility of the hybrids along with the degeneration of the endosperm resulted in the production of unfilled F2 seeds. Drastic reduction in the germination of F2 and F2M2 seeds was recorded. A preponderance of low yielding yellow vein mosaic resistant plants similar to the donor parents was observed among the F2 and F2M2 populations indicating the presence of powerful genetic mechanisms preventing free recombination. As compared to F2's, the proportion of recombinants was higher in the F2M2 population, indicating the breakage of undesirable linkages through irradiation. Both positive and negative transgressive variants for the different characters were seen in the F2 and F2M2 generation. Based on superiority in performance fifty seven plants were selected, in which six plants recorded an yield greater than 525 g per plant. Maximum number of recombinants were identified in the
irradiated crosses, A. caillei x Aanakkompan (T1 x L1I) and A. caillei x Eanivenda (T1 x L2I). These recombinants had higher yield than the check variety 'Punjab Padmini' coupled with YVMD resistance confirmed by graft inoculation. These lines can be utilized in further breeding programmes for evolving high yielding resistant varieties in Bhindi.