PhD

The present investigations on improvement of Dendrobium through
hybridsation and in vitro mutagenesis were conducted in the Department of
Pomology and Floriculture, College of Horticulture, Vellanikkara, during 1996-
1999.
Ten varieties and six species of Dendrobium were included for the trial.
All the varieties showed significant variations among themselves for the characters
studied. New Pink had the highest number of shoots (9 Nos.), maximum leaf
length (15.17 cm), largest flowers (8.27 cm x 7.9 cm) and longest vase life (18.33
days). Number of flowers was maximum for Candy Stripe (11.67 Nos.)
Anthesis in Dendrobium was observed between 7.30 am and 2.30 pm
and the stigma receptivity period ranged from second to 10th day of flower
opening, in different varieties.
Pollen out put ranged from 2720 (Dendrobium pierardii) to 13120
(Emma White). Pollen grains were found as agglutinated masses called pollinia
and each flower had two pollinia.
Sabine had the maximum pollen size (47.46 u). Pollen fertility of the
hybrids ranged from 46.77 per cent (D. chrysanthum) to 91.93 per cent (New
Pink). Maximum pollen germination occurred in two per cent sucrose + 1 per cent
agar (80.33%) as well as in 2 per cent sucrose + 2 per cent agar (78.00%). Emma
White had the maximum pollen germination (80.63%).
Heritability was of moderate to high magnitude. Genotypic correlation
coefficients were found to be higher than phenotypic correlation coefficients,
indicating lesser environmental effects on the characters.

The characters having significant positive correlation with number of
flowers per spike were mean height of the shoots, total number of leaves, length of
inflorescence, days for opening of all florets and internodal length of first two
florets.
All the varieties, except Hieng Beauty, were self compatible. Emma
White had the maximum cross compatibility as the female parent and Sabine had
the least. Emma White, New Pink and Pink Tips performed as good male parents.
Out of the six species tried, D.fimbriatum gave the maximum cross compatibility.
When green pod culture was employed, 90-110 days old pods gave the
best results in culture. Mercuric chloride treatment (0.1%) for one minute,
followed by alcohol dip and flaming was found to be the best surface sterilization
method for pods.
Germination percentage of hybrid seeds was minimum in New Pink x
Dendrobium crumenatum and maximum in New Pink x Emma White. Pink Tips
selfed seeds gave 100 per cent germination. Maximum for planting out was taken
by Sonia-28 x D. crumenatum seedlings (385 days) and minimum by Emma White
selfed seedlings (253 days).
Growth hormones like kinetin and IBA, each at 1 mg r' and 2 mg r',
gave better germination. Early germination, protocorm formation as well as shoot
and root production were observed in the medium containing kinetinlBAP at
4 mg r' to 8 mg r' and IBAlNAA at 2 mg r' to 6 mg r'. These media also gave
higher values for seedling characters like height, number of leaves, leaf length,
number of roots and root length.
With regard to the different sucrose levels, that at 0.5 per cent gave best
seedling growth. Charcoal at 0.5 per cent gave early germination and early shoot
and root formation and at 1.0 per cent level gave best seedling growth.


Regarding the effect of media supplements, coconut water at 150 ml r'
and peptone 1000 mg l' gave best seedling growth. Adenine at 4-6 mg r' also had
a favourable effect on seedling characters.
Callus formation was favoured by NAA 4 mg rl + 2,4-D - 2 mg r'
along with kinetin 2 mg r'. Formation ofPLBs from in vitro leaf was obtained in a
medium containing BAP 25 mg r' + NAA 2 mg r'.
Protocorms, PLBs and callus were subjected to in vitro mutagenesis
using gamma rays up to 60 Gy. As the dose of irradiation increased the height was
reduced. Higher doses of irradiation produced smaller and broader leaves with dark
green colour. Survival rate was found to decrease in the irradiated materials. At
60 Gy the PLB and callus did not survive.
Planting out of different hybrid seedlings was successfully carried out in
the field. Equal proportion of charcoal pieces and brick pieces was used in the
medium. Survival of the hybrids ranged from 14 per cent in New Pink x
D. chrysanthum to a maximum of 94 per cent in New Pink selfed. The seedlings
were maintained by regular nutrient and pesticide sprayings.
Out of the different nutrient solutions tried 30:10:10 NPK mixture (0.1 -
0.2%) sprayed on alternate days gave best results in terms of number of shoots and
number of leaves.
Regarding the effect of growth hormones, BA at 50 mg r' at fortnightly
intervals gave maximum number of shoots and leaves, followed by BA 25 mg rl.
Maximum height of the seedlings was obtained with GA 10 mg r' sprayed at
fortnightly intervals.
Field evaluation of the hybrids revealed variations in the growth and
floral characters.