PhD

Bitter gourd (Momordica charantia L.) is one of the important cucurbitaceous vegetable valued for its nutritional and medicinal properties. Bitter gourd has been in use for centuries in the traditional system of medicine of several countries like India, China, Africa, and Latin America. Even though, cultivated bitter gourd (M. charantia var. charantia) is highly vulnerable to most of the pests and diseases, its wild/semi-domesticated type (M. charantia var. muricata) is endowed with resistance/tolerance to some of the common pests and diseases of cucurbits. In bitter gourd, the major disease prevalent in south India is powdery mildew caused by fungus, Erisiphe cichoracearum. The disease severity even goes up to 80 per cent during December – January. The identification of resistance sources to major pests and diseases is essential for developing resistant cultivars. Attempts to develop disease resistant cultivars in bitter gourd by earlier workers have not found much success. The present study was taken up in this background at COH, Vellanikkara during 2014-18 to characterize and screen the selected accessions of wild/semi domesticated bitter gourd (M. charantia var. muricata) for powdery mildew resistance and to assess the possibility of transferring this tolerance/resistance to commercial varieties. Fifty accessions of wild/ semi domesticated bitter gourd and three check varieties viz., Preethi, Priyanka and Pusa Purvi formed the material for the study. These accessions were subjected to morphological and biochemical evaluation. The morphological evaluation based on 35 qualitative and 28 quantitative characters was done using the descriptor developed by NBPGR (2001). Vitamin C, iron, fibre content and total antioxidant capacity were estimated following standard procedures for biochemical characterization. Clustering based on quantitative characters was done following agglomerative hierarchical clustering method. Wide variability was observed among the accessions for all the qualitative traits except primary leaf shape and margin, stem pubescence, stem shape, leaf margin, leaf shape, fruit ribs and blossom end shape of fruit. Variation expressed by the accessions in terms of both fruit and seed quantitative traits was also high. Among the wild genotypes, IC 467681 was having the highest fruit weight, fruit length and fruit width. However, its yield was only 969.49 g/plant. The highest yield was observed in the cultivated types followed by AC-16/1 (1493.88 g). The cluster analysis based on quantitative characters resulted in four clusters at 90 per cent similarity level. Clustering clearly separated wild genotypes from cultivated ones by placing Preethi and Priyanka in cluster III and IV respectively. High heritability coupled with high genetic gain was observed (>20%) for number of fruits per plant, yield per plant, fruit length, number of seeds per fruit and 100 seed weight. The biochemical characters viz., Vitamin C, iron, fibre content and total antioxidant capacity ranged from 76.53 to 125.67 mg/100 g; 1.48 to 3.31 mg/100g; 12.17 to 30.44 per cent and 41.88 to 92.01 mg AAE/g respectively. Based on organoleptic evaluation, the maximum score for overall acceptability was obtained for Priyanka followed by Preethi and AC-16/1. All the bitter gourd accessions were screened under natural field conditions during 2016 and 2017 for their reaction to powdery mildew and mosaic diseases. Based on per cent disease severity of the accessions during two consecutive crop seasons, five accessions viz., IC 213312, AC-16/1, AC-16/4, AC-16/9, and AC-16/21, which were resistant to both diseases were identified and crossed with susceptible check varieties in Line × Tester design. All the fifteen hybrids along with five parents were evaluated for powdery mildew tolerance/resistance and yield characters. Nine crosses were immune to powdery mildew disease. The better performing wild genotypes with respect to yield, fruit weight, organoleptic score and resistance, viz., AC-16/1, AC-16/16, IC 467681 and JJNS-15/65, should be further tested in large scale yield trials and recommended for commercial cultivation especially for homestead farming.