PhD

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.