PhD

The research project “Characterization and in vitro multiplication of bittergourd (Momordica charantia L.) genotypes” was carried out at the Department of Olericulture, the Department of Plant Biotechnology and the Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani during 2005-2008. The objective of the study was to catalogue the genotypes based on the IBPGR descriptor for cucurbits, to estimate the genetic parameters for different traits in the germplasm for identifying superior lines based on yield, quality, pest and disease resistance, to document the biochemical traits, to characterize the genotypes using molecular techniques (RAPD analysis) and to standardize the in vitro techniques for bittergourd.
Thirty three genotypes of Momordica charantia collected from various sources upon cataloguing pointed out wide variation for several morphological characters. Analysis of variance revealed significant differences among the genotypes for all the characters except fruit fly infestation (%) studied namely, days to seedling emergence, vine length, internodal length, number of primary branches, number of secondary branches, days to first male flower, days to first female flower, node to first male flower, node to first female flower, sex ratio, days to first fruit harvest, fruit length, fruit girth, fruits per plant, average fruit weight, yield per plant, seeds per fruit, 100-seed weight and mosaic incidence.
Among the genotypes, MC 20 (Priyanka, KAU) recorded the maximum yield (5.89 kg), average fruit weight (578.75 g), fruit length (38.83 cm) and fruit girth (25.53 cm). MC 1 was the longest in vine length (620.00 cm). MC 33 (1.25 cm) was shortest in internodal length along with least vulnerability index for mosaic (10.00). MC 10 was characterized by maximum fruits per plant (34.25). MC 16 was the earliest to flower (36.00 days for female flowering) while, MC 32 was the earliest to harvest (43.50). High phenotypic and genotypic coefficients of variation were observed for yield per plant and average fruit weight.
High heritability coupled with low genetic advance was observed for most of the characters. High heritability coupled with high genetic advance was observed for vine length and average fruit weight.
Correlation studies and path coefficient analysis revealed that average fruit weight and number of fruits per plant are the primary yield components as evidenced from its high positive correlation as well as direct and indirect effects on yield.
In the discriminant function analysis, the genotype MC 20 (Priyanka, KAU) ranked first, followed by MC 10 (MDU-1, TNAU), MC 26 (Thripunithara, Ernakulam), MC 22 (Chathamangalam, Kozhikode) and MC 27 (Charuplasseri, Palakkad). They were found to be promising based on their superiority in yield, fruit quality, earliness in male and female flowering, narrow sex ratio, fruit fly infestation and mosaic resistance and hence they may be utilized for further crop improvement.
Based on the analysis for genetic divergence, the 33 genotypes of M. charantia were grouped into five clusters, with the highest intercluster distance observed between clusters III and IV.
The keeping quality studies indicated that maximum shelf life, lower percentage loss in weight, lowest rotting percentage and slower change in colour was obtained from fruits of the genotype MC 25.
The organoleptic quality evaluation revealed that all the genotypes differ significantly for attributes like appearance / colour, doneness, flavor, taste and bitterness. In general, fruits with light green skin colour had overall acceptability and were superior to others based on the score.
The biochemical characterization revealed that the medium sized fruits were associated with higher β-carotene while, small sized fruits found to have higher iron content and large fruited genotypes contained higher ascorbic acid content. Genotypes with higher the chlorophyll content, greater will be the bitterness value. A distinct difference in the content of vitamins and minerals is observed in different genotypes. However, correlation between colour of fruits and their iron content is found in some of the genotypes.
The DNA isolated from the 33 genotypes of M. charantia were subjected to RAPD analysis. Out of the 80 decamer primers, fifty six yielded amplification products. A total of 158 RAPDs (average 1.98 bands per primer) were generated by the 56 primers, of which 86.08 per cent were polymorphic (136 bands) and twenty two were monomorphic. Eight primers viz., 0PA-02, 0PA-18, OPB-01, OPB-06, OPB-12, OPE-14, UBC-03 and UBC-05 showed high level of polymorphism and were informative enough to analyse the genotypes The selected primers yielded 56 scorable bands (average of 7.00 bands per primer) of which 23 were monomorphic and rest, 33 were polymorphic (58.93 %). The overall Jaccard’s similarity coefficients ranged from 0.65 to 0.90. Cluster analysis revealed that at about 0.65 similarity coefficient, the thirty three genotypes of M. charantia grouped into two clusters which clearly separates genotypes based on average fruit weight and fruit skin colour.
By characterizing all the thirty three genotypes of Momordica charantia using morphological (selection index and D2 analysis) and molecular (RAPD marker analysis) methods revealed that morphologically distinct and superior lines were genetically differentiable. The clustering pattern based on yield related traits and molecular variation was different. Also, the diversity based on yield related traits and molecular analysis was not in consonance with ecological distribution.
The induction of potentially organogenic callus and better proliferation of callus successfully from all the explants was obtained either on the MS medium supplemented with IBA (4.00 mg l-1) + BA (0.50 mg l-1) + 2,4- D (2.00 mg l-1) or NAA (2.00 mg l-1) + BA (0.50 mg l-1) + 2,4- D (2.00 mg l-1) in combination with 30.00 g l-1 sucrose and 6.30 g l-1 agar level. The shoot tip explants were more responsive among all the explants tried in terms of callus induction and subsequent plant regeneration. Shoot regeneration response from shoot tip derived callus was best on MS medium fortified with 0.05 % AC + 1.00 mg l-1 BA with earlier regeneration, highest regeneration percentage, lengthy adventitious shoot and more number of leaves under light conditions.