PhD

An investigation on "Intra and interspecific hybridization in
Dendrobium spp." was carried out in the Department of Plant Breeding
and Genetics, College of Agriculture, Vellayani, during 1998-2001 with
the objective of developing new hybrids of Dendrobium with novel,
commercial cutflower qualities for the export market. Fourteen genotypes
of Dendrobium comprising of nine commercial varieties, three semi-
commercial varieties and two species were selected as parents after initial
evaluation. The parental genotypes differed significantly with respect to
all the 21 characters studied. High heritability combined with high GCV
and genetic advance were observed for length of inflorescence, length of
scape, number of flowers per inflorescence and number of nodes per cane.
Significant positive inter-correlation in all pair-wise combinations at
genotypic and 'phenotypic levels was observed between seven characters
viz., number of leaves per clump, height of cane, leaf area per cane, age
at first flowering, cane to flower first, vase life and length of
inflorescence.
The 14 parental genotypes were crossed in all possible
combinations (196) after preliminary studies on floral biology, anthesis
and pollination. Six combinations could not be attempted as the flowering
seasons of the genotypes concerned did not synchronise. A total of 1696




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pollinations were done covenng 190 (88 crosses + 88 reciprocals + 14
selfs) combinations. Pollinated flowers/immature capsules from 106
combinations abscised at different stages. Green capsules were harvested
from 84 combinations. Capsules from three combinations did not contain
seeds and seeds from five combinations did not germinate on inoculation.
Protocorms/developing seedlings from seven combinations aborted at
various stages of in vitro development. Seedlings from 69 combinations
were deflasked and transplanted. Two combinations failed to get
acclimatized. Progeny from 67 (62 crosses and five selfs) combinations
were established successfully in the green house. The levels of
incompatibility reactions were grouped under nine heads ranging from
flower abscission before the onset of any visible post pollination change
to failure of hybrid seedlings to get acclimatized to the ex vitro green
house conditions. A total of 123 combinations attempted succumbed to
incompatibility at these different stages. Percentage capsule yield ranged
from 8 to 33 in the various hybrid combinations. Percentage filled seeds
ranged from 10.79 to 75.93 and percentage seed germination ranged
from 8.00 to 70.73. The basal medium MS half strength was the best
for early germination and rapid in vitro development as compared to MS
quarter strength and MS, KC and VW full strengths. The effects of growth
hormones, organic additives, sucrose and charcoal on in vitro seed germination
and seedling growth were studied and the best concentrations were identified.
Transplanting into the humidity chamber under conditions of high
relative humidity (85-95%) and controlled irrigation resulted in 94 per
cent survival after four weeks. The best among the potting media tried




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was broken tiles + charcoal + Soilrite (2:2:1), favouring high survival
and well balanced post transplantation seedling growth. The 67 hybrid
combinations differed significantly with respect to all the eight vegetative
characters studied at 1.5 to 2.0 years after transplanting. A partial diallel
established with 18 cross combinations revealed the gca effect of P3 to
be beneficial for number of shoots per clump, as it was positive and
significant. Non additive gene action was responsible for character
expression, as dominance variance was higher than additive variance.
Sixteen hybrid combinations flowered, recording significant differences
for all the 12 floral characters studied. Economic heterosis, relative
heterosis and heterobeItiosis of the hybrid combinations were studied
for all vegetative and floral characters recorded. Considerable vegetative
vigour, earliness and increase in the size of flowers and inflorescences
were registered by the hybrid combinations.
From the 16 flowering combinations, about 40 promising hybrids
were identified. Based on three important criteria viz., novelty,
distinctiveness and uniformity of the floral characters, 25 out of these
40 new hybrids were selected. These hybrids show the potential for
development into new, indigenous commerical varieties.