PhD Thesis
Permanent URI for this collectionhttp://localhost:4000/handle/123456789/48
Browse
3 results
Search Results
Item Genetic improvement in Dendrobium orchids through hybridization and molecular characterization(Department of Plant Breeding and Genetics, College of Agriculture,Vellayani, 2023) Amrutha Unni, M.; Beena ThomasThe present study entitled “Genetic improvement in Dendrobium orchids through hybridization and molecular characterization’ was carried out at Department of Plant Breeding and Genetics, College of Agriculture, Vellayani, during 2018-2022, with an objective to assess the genetic variability in commercially important Dendrobium orchids to develop superior hybrids and confirming hybridity through molecular markers. Twenty Dendrobium orchid genotypes with desirable traits and widespread market acceptance were collected, planted in the greenhouse and assessed for variability, heritability, genetic advance and correlation. Analysis of variance showed significant differences among the genotypes for all the characters studied. For the majority of the analysed traits, the mean performance has a broad range of variation among the parents. D. Thong Dang Yellow showed higher mean performance for internode length and plant height. Of the 20 genotypes, 15 flowered, while five genotypes failed to flower due to environmental factors and less adaptations. So the floral characters of 15 genotypes were studied. D. White represented desirable mean values for inflorescence diameter and inflorescence number per plant, D. Rabit Gold showed higher mean performance for pollen fertility and days to first flower opening from inflorescence, D. Gift by God Candy showed higher mean value for flower width in front view and days to last flower opening from first flower and D. Burana Pearl x D. Burana White showed higher peduncle length and vase life. For the vegetative characters, the thickness of leaf exhibited the highest GCV (66.16%) and PCV (69.54 %). High heritability coupled with high genetic advance was recorded for plant height, number of leaves per shoot, number of aerial roots, length of aerial roots, thickness of the shoot, internodal length, length of the leaf and leaf area which indicated that these traits were controlled by additive gene action. For the floral characters the maximum PCV and GCV were found in flower width in front view. All the floral characters showed high heritability along with high genetic advance, demonstrating that these traits were controlled by additive gene action. Plant height showed the strongest positive correlation with the number of aerial roots among the vegetative characters. Significant highly positive correlation was found between the number of inflorescences per plant and the inflorescence axis diameter. Days to first flower opening from inflorescence emergence recorded significant positive correlation with inflorescence axis diameter. Out of the 15 genotypes studied, three genotypes exhibited seasonal flowering nature and all others were free flowering. Inflorescence axis was found to be pendulous in D. Yaya and the rest of the genotypes produced erect or arching type of inflorescence axis. Flower fragrance were present in D. Red Fairy, D. Thong Dang Yellow, D. Popeyes and D. Gift by God Candy. Shape of flower was found as full and round, flat and surfaced with broad sepals and petals. In the study, thirty ISSR primers were used to examine the genetic diversity of 20 orchid hybrid genotypes used in this study. A total of 102 bands were produced, out of which 57 bands found were polymorphic and 45 bands were monomorphic in nature. Polymorphic information content value of the primer ranged between 0- 0.49. Dendrogram was generated using NTSYS-pc 2.02e software and the twenty genotypes were grouped into five clusters. Divergent lines identified were D. Pink bfc, D. Pearl Red Lip and D. King Dragon. The best ten parental genotypes were crossed based on flower synchronization and availability of pollen. A total of 20 cross combinations were attempted. Incompatibility reactions were noticed at different stages ranging from flower abscission before the onset of any visible post pollination change to instances where seeds germinated but aborted in culture. Mature green capsules were harvested from 12 combinations at 70 to 90 per cent maturity. The 12 combinations were inoculated in vitro, but four of them did not produce any seeds in the capsule and one did not germinate. All seven in vitro cultured combinations were successfully germinated and were sub cultured three to four times. The basal media used for the in vitro propagation was half MS. The in vitro growth of the hybrid Dendrobium was improved by supplementing with BA (1 mg/l), IAA (0.1 mg/1) and charcoal (4g/l) was found to be effective. Deflasked seedlings with three or more leaves and three or more roots were then transferred in half MS media. There was significant variance among the number of days required for germination, protocorm development, emergence of first leaf, the first shoot, the first root primordia and deflasking. At deflasking, there were noticeable variations in seedling morphology among the seven hybrid combinations. The present research work identified 10 commercially popular hybrid genotypes that excelled in floral features and diversity attributes. The hybrid plantlets developed through hybridization are to be hardened and maintained in net house for evaluation of morphological and floral traits. These can be utilized in further crop improvement programmes in Dendrobium.Item Introgression of mosaic resistance in popular short duration cassava varieties of Kerala through marker assisted selection(Deparment of Plant Breeding and Genetics, College of Agriculture, Vellayani, 2018) Darshan, S; Arya, KThe present study entitled “Introgression of mosaic disease resistance in to popular short duration cassava varieties of Kerala through marker assisted breeding”was conducted in the Department of Plant Breeding and Genetics, College of Agriculture, Vellayani, Kerala Agricultural University and Division of Crop Improvement, ICAR- Central Tuber Crops research Institute, Sreekariyam, Thiruvananthapuram, Kerala during the period 2014 - 2017 with the core objective of introgression of cassava mosaic disease (CMD) resistance to short duration varieties of cassava through marker assisted selection (MAS) and to study the inheritance of early bulking nature. The research work was carried out as four experiments. In the first experiment, Five early bulking high yielding lines viz, Sree Jaya, Sree Vijaya, Vellayani Hraswa, CI 889 and 9S 75 and three testers viz, CR 54A3, IMS2-5 and CI 273 with resistance to cassava mosaic disease were selected and planted in a pollination block and crossed in Line x Tester (LxT) design to produce hybrid seeds of 15 F1 combinations. Experiment II was conducted in two parts. Screening of F1 seedlings for CMD resistance and early bulking nature was carried out in the first part of experiment II, where hybrids along with the parents were evaluated. Analysis of variance revealed significant differences among the genotypes for all the traits studied. All the agronomic traits were recorded and inheritance of early bulking and its correlation with other traits were studied. The CMD incidence expressed significant and negative correlation with tuber yield per plant where as significant and positive correlation for all other traits with tuber yield per plant was observed among the F1’s. As a part of experiment II (b), seedlings without the CMD visual symptoms were subjected to multiplex PCR and the results revealed that among the parents Sree Jaya, Sree Vijaya, Vellayani Hraswa expressed presence of Srilankan Cassava mosaic Virus (SLCMV) and Vellayani Hraswa expressed the presence of both SLCMV and Indian Cassava mosaic Virus (ICMV). Among the crosses, Sree Jaya x CR54 A3 (L1x T1), Sree Jaya x IMS2-5 (L1xT2), Vellayani Hraswa x IMS2-5 (L3xT2), CI 889 x CI 273 (L4xT3) expressed the presence of SLCMV. Real time PCR (qPCR) assay for seedlings identified CI 889 (L4), 9S 75(L5), CR 54A3 (T1), IMS2-5 (T2) and CI 273(T3) among the parents and Sree Jaya x CR54 A3 (L1x T1), Sree Jaya x IMS2-5 (L1xT2), Sree Jaya x CI 273(L1x T3) and 9S 75 x CR54 A3 (L5x T1), 9S 75 x IMS2-5 (L5xT2) and 9S 75 x CI 273 (L5x T3) among the crosses as highly resistant, based on viral load present in the DNA sample. Based on the previous report ten CMD resistance linked markers were screened through BSA and five of which SSRY 28, SSRY 44 SSRY 40, SSRY 106 and SSRY 235 were selected. Among the CMD linked SSR markers studied, the maximum polymorphism was elucidated by SSRY 28, SSRY 44 and followed by SSRY 235. SSRY 28 is a strongly linked marker to CMD2 which is a dominant gene conferring resistance among the clones of combinations (L1xT1, L2xT2, L3xT1 and L3xT3) three of five markers revealed alleles associated with CMD2 gene In the third experiment to evaluate the early bulking clones, field was laid out in randomized block design (RBD) with three replications consisting of CMD resistant clones along with parental clones using miniset technique. Analysis of variance revealed significant differences among the genotypes for all the traits. Measurement of heterosis was carried out considering parent Vellayani Hraswa (L3) as check and results revealed that standard heterosis was positive and significant in the combinations Sree Jaya x CR 54A3 (L1xT1) and Sree Jaya x CI 273 (L1xT3) for all the yield contributing traits. The crosses Sree Jaya x CR54 A3 (L1x T1) and Sree Jaya x CI 273 (L1xT3) exhibited negative standard heterosis for CMD. Combining ability analysis showed significant gca, sca variances and gca, sca effects for all the traits. Moreover gca/sca variance ratio indicated preponderance of dominance / non-additive gene action for the inheritance of all traits. Among the lines, Sree Jaya (L1) exhibited positive and significant gcaeffect for tuber yield and yield contributing traits. Among the testers, IMS2-5 (T2) exhibited negative and significant gca effect for CMD. Among the crosses Sree Jaya x CR54 A3 (L1x T1) exhibited positive and significant scaeffect for girth of tuber and stem girth, 9S 75 x CI 273 (L5xT3) exhibited positive and significant scaeffect for tuber yield per plant, CI 889 x CR 54A3 (L4xT1) exhibited negative and significant scaeffect for CMD. In the last experiment, through bulk segregants analysis using 5 SSR markers linked to early bulking in cassava were selected out of 9 SSR markers selected. Among 5 SSR markers of CMD and early bulking nature two SSR markers (SSRY 28 and SSRY 106) associated with resistance to CMD and One SSR marker, ESTs (SSRY) 292 associated to early bulking nature has been identified. Among the crosses, clones from Sree Jaya x CR54 A3 (L1xT1), Sree Jaya x CI 273 (L1x T3) and 9S 75 x CR 54A3 (L5xT1) are being confirmed with CMD resistance as well as early bulking nature.Item Genetic diversity and combining ability in cucumber (Cucumis sativus L.)(Department of Plant Breeding and Genetics, College of Horticulture, Vellanikkara, 2017) Suma, A; Elsy, C RAssessment of genetic diversity is the key tool in any crop improvement and germplasm management programme. Evaluation of genetic variation will help to provide valuable information about new sources of genes. The studies on combining ability and heterosis can support utilization of promising lines in further crop improvement programmes. Cucumber (Cucumis sativus L. 2n= 2x= 14) is an indigenous vegetable crop of India. Even though rich diversity for cucumber is available in India, studies on genetic diversity of this crop are scanty. Therefore, the present project was proposed to explore genetic diversity in cucumber using morphological and molecular markers and to study combining ability and heterosis in selected genotypes. Morphological characterization of 50 accessions of cucumber revealed presence of significant difference among accessions for majority of vegetative, floral and fruit characters. Mean days to first male and female flower opening was 36 and 43 days respectively. Majority of the accessions possessed elliptical elongated fruits with light green skin colour and white flesh colour. Sixteen accessions exhibited significantly higher fruit length than AAUC-2, the standard check, the maximum being exhibited by IC613472 (20.85 cm). Accessions with oblong ellipsoid fruits possessed higher fruit diameter. Mean fruit weight showed high variability among accessions with a range of 33 g to 343 g. Fourteen accessions exhibited significantly high yield than AAUC-2. Number of fruits per plant, yield per plant, loss of weight during storage and sex ratio showed high values for all the genetic parameters studied. IC613481 was the promising genotype identified in morphological characterization, followed by IC613480. Cluster analysis grouped accessions into seven distinct clusters based on the level of similarity in quantitative characters. Random grouping of accessions into various clusters indicated absence of parallelism between genetic diversity and geographical diversity. Cluster II and III were the largest clusters, with 14 accessions each and Cluster V and VI, the smallest ones with single accession each. Results of Principal component analysis revealed that first three principal components, with Eigen values more than unity accounted for 85.80 per cent of cumulative variance, contributed by fruit weight, fruit length, fruit diameter and days to first harvest. The diversity analysis of the accessions was done using DIVA-GIS by generating grid maps. The results of the study indicated that highly diverse accessions with respect to the selected characters were sourced from Mizoram, Tripura and West Bengal. Molecular characterization revealed high level of genetic distinctness between genotypes. SSR11742 and AF202378 were found to be highly polymorphic markers, with high polymorphism information content and number of polymorphic bands. In-depth evaluation of selected 22 genotypes revealed significant difference for all fruit characters except days to last harvest and harvest duration and further revealed the superiority of IC613480. Evaluation of 15 hybrid combinations developed through half diallel mating design and their parents indicated presence of significant difference among parents and hybrids for various characters studied. Among the parental genotypes, IC613480, exhibited significantly high GCA effects for fruit length, number of fruits per plant and yield per plant whereas IC595508A, for fruit weight and loss of weight during storage, and IC613485 for fruit diameter, thus proving to be promising parents for accumulating genes for these characters. The hybrids, IC613480 x IC595508A and IC613480 x IC613471 showed significant SCA effects for yield per plant and sex ratio. IC613480 x IC613471, IC613480 x IC595508A and IC613471 x IC595508A were exhibiting significantly high relative heterosis, heterobeltiosis and standard heterosis for number of fruits per plant and yield per plant. IC613480 and IC613485 were the most promising genotypes identified from the study whereas IC613480 x IC613471 was the most promising hybrid based on SCA effects, heterosis, per se performance on yield contributing characters and organoleptic qualities. This hybrid showed high fruit length (17.01 cm), yield per plant (2163.45 g), number of fruits per plant (11.43) and sex ratio (0.11). IC613480 x IC613476 and IC613485 x IC595508A were the other promising hybrids.