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|Advisor:||wfehe, Dr. b.5|
|Title:||STUDIES ON INTERSPECIFIC HYBRIDIZATION FOR RESISTANCE TO YELLOW VEIN MOSAIC VIRUS IN OKRA|
|Publisher:||MAHATMA PHULE KRISHI VIDYAPEETH, RAHURI-413 722, DIST. AHMEDNAGAR, MAHARASHTRA STATE, INDIA|
|Abstract:||The present investigation entitled "Studies on inter-specific hybridization for resistance to yellow vein mosaic virus in okra" was conducted at All India Co-ordinated Vegetable Improvement Project, Department of Horticulture, M.P.K.V., Rahuri, during the year2002-2005. The main objectives of the study were initial screening of wild and cultivated types of okra for resistance to YVMV, studying cross compatibility and inter-specific hybridization between wild and cultivated types, screening inter-specific hybrids and their parents forresistance to YVMV, confirming the hybridity of inter-specific Fi hybrids through proteinelectrophoresis, evaluating biochemical basis of resistance to YVMV and development ofbackcrosses in resistant inter-s ecific F^ hybrids.The initial programme comprised of screening twenty one wild lines of nine Abelmoschus spp. and ten cultivated A. esculentus cultivars obtained from different centers to identify the source of resistance to YVMV and other important diseases and pests. The results revealed that wild parents A. tetraphyllus lines 1,2,3 and 4, A. moschatus lines-1, 2,3,4 and 5, A. caillei-2, A. angulosus, A. manihot (L.) Medikus and A. manihot spp. Tetraphyllus were found highly resistant to YVMV; the wild lines A. caillei-2 and A. moschatus-4 werefound immune to powdery mildew; all wild lines screened were found resistant to Cercosporaleaf spot; A. moschatus lines 1,2,3,4 and 5 were found to have least jassid (nymph)population per leaf; A. moschatus lines 1,2,3,4 and 5 and A. angulosus were found to haveminimum mean whitefly (adult) population per leaf and A. tuberculatus lines 1,2 and 3 were found to be immune to fruit borer infestation while A. tuberculatus lines 1,2 and 3, tetraphyllus lines 2,3,4 and 5 and A. manihot spp. tetraphyllus were found completely free from shoot borer infestation. All the cultivars of A. esculentus except Red Bhendi were foundresistant to Cercospora leaf spot under Rahuri conditions. However, none of the cultivated A.esculentus cultivars screened were observed resistant to other major diseases and pests ofokra. From the initial screening programme, eight cultivars of A. esculentus andeleven wild lines of nine Abelmoschus spp. were selected for inter-specific hybridization. In allthe crosses, cultivated types were used as female parent except the crosses with A. caillei-2where both direct and reciprocal crosses were attempted and fifty-three crosses were developed. The results of cross compatibility studies revealed that A. moschatus-l was found incompatible with A. esculentus while A. ficulneus-~\ was found compatible but seed sterile, however, remaining wild species were found compatible with A. esculentus cultivars. Majority of morphological characters, growth characters and yield and yieldattributing characters studied in F, hybrids were found intermediate between their parents. Allthe hybrids exhibited heterosis for the characters such as plant height, number of nodes percaillei-2 as one of its parents) exhibited heterosis for the characters fruit length and girth.However, the yield of all the hybrids were found to be lower than both the parents except A.caillei-2 hybrids, which yielded in between their parents.Screening inter-specific okra F, hybrids for resistance to major diseases andpests for two seasons revealed that seven hybrids were found highly resistant to yellow veinmosaic virus; A. caillei-2 hybrids were found highly resistant to powdery mildew; all hybridsexcept Red Bhendi hybrids (hybrids having Red Bhendi as one of its parents) were foundhighly resistant to Cercospora leaf spot; all hybrids were found to have intermediate whitefly (adult) and jassid (nymph) population per leaf between their parents and A. tuberculatus--\hybrids (hybrids having A. tuberculatus-1 as one of its parents)were found to be highly resistant to shoot and fruit borer incidence. The highly resistant hybrids tested under field epiphytotic conditions were further tested for YVMV resistance by artificial inoculation throughgrafting.Electrophoretic protein profile of all wild and cultivated lines screened was tudied for their characterization as well as inter-species divergence in okra. Similarity index calculated on the basis of protein band homology established more divergence of thecultivated A. esculentus with A. moschatus and A. ficulneus. The wild species A. manihot pp.tetraphyllus was found to be the closest to A. esculentus on the basis of band homology. Thehybridity of twelve YVMV resistant (7- highly resistant and 5 resistant) interspecific hybridswas also confirmed by total protein analysis (derived from seed proteins) on the basis ofhybrid specific bands, intermediate bands, total number of bands and with different bandintensities. Furthermore, for confirmation of hybridity, the bands obtained in total protein analysis were also used to calculate similarity index of interspecific Fi hybrids with their parents (8.33 to 61.53 % with female parent and 9.09 to 54.54 % with male parent) was observed which also proved hybridity of Fi plants. The wild parents resistant to YVMV had maximum phenolics, peroxidase, polyphenol oxidase activity and seed soluble protein content while cultivated okra had minimum whereas inter-specific hybrids recorded in between their parents. However, sugar (reducing, non reducing and total) and total nitrogen content were found minimum in resistant wild parents, maximum in cultivated okra and intermediate in case of inter-specific hybrid . In YVMV resistant plants infected with YVMV, phenolic content decreased and peroxidase an polyphenol oxidase activity, total nitrogen and sugar content increased when compared with YVMV resistant healthy plants while an exact opposite trend was observed in the YVMV susceptible healthy and infected plants. The correlation studies between biochemicalparameters, pest and YVMV co-efficient of infection revealed that a positive significantrelationship was observed between the characters total nitrogen, reducing and total sugars,mean whitefly (adult) population per leaf, powdery mildew incidence and yellow vein mosaicvirus co-efficient of infection while a negative significant relationship of characters total phenolics, seed soluble protein, days to first appearance of YVMV with YVMV co-efficient ofinfection was recorded. Nevertheless, ten inter-specific okra F, hybrids were utilized in backcrossbreeding programm where direct and reciprocal backcrosses to corresponding A esculentus cultivars and direct back crosses to wild parent was undertaken. Only A. caillei-2 hybrids were found successfully yielded seed in direct backcrosses to both wild A caillei-2 and A. esculentus parents. However, reciprocal backcrosses were successfully yielded seed in other hybrids studied but the backcross hybrid Varsha Uphar x (Varsha Uphar x A. manihot spp.tetraphyllus) only germinated. Majority of the inter-specific okra F^ hybrids were found sterile except thehybrids having A. caillei-2 as one parent. Inter-specific hybrids having A caillei-2 as one of itsparents produced 0-4 seeds per fruit. The F2 generation studies revealed poor germination inthe hybrids having A caillei-2 as one parent.Thus, the present study revealed that seven inter-specific F-, hybrids werefound highly resistant to YVMV and powdery mildew under field epiphytotic conditions andtheir resistance to YVMV was further tested by artificial inoculation of virus through grafting.The hybridity of Fi hybrids have been confirmed through protein electrophoresis. Biochemicalbasis of resistance to YVMV in these hybrids have also been established.|
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