Genetic improvement in Dendrobium orchids through hybridization and molecular characterization

Abstract

The 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.