PhD

The present investigation entitled “Distant hybridization and compatibility
studies in wild orchids” was carried out with the objective of studying the cross
compatibility through distant hybridization in wild orchids and molecular
characterization of hybrid seedlings using RAPD/ISSR- markers. The study was
carried out at Saraswathy Thangavelu Extension Centre of KSCSTE- JNTBGRI,
Puthenthope, Thiruvananthapuram and at College of Agriculture, Vellayan,
Thiruvananthapuram.
The research work included experiment I, II, III and IV. Experiment I was
carried out in two parts as evaluation of parents and hybridization, experiment II
was cross compatibility studies of selected species, experiment III was in vitro
culture of resultant hybrids and evaluation of seedlings and experiment IV was
molecular characterization of hybrids.
In experiment I, wild types belonging to different genera/species namely
Vanda (Vanda tessellata, Vanda spathulata, Vanda sp.), Rhynchostylis retusa,
Spathoglottis (Spathiglottis albida,
Spathoglottis unguiculata, Spathoglottis
gracilis, Spathoglottis plicata), Aerides ringens and
Arundina graminifolia
available at the orchid conservatory of Saraswathy Thangavelu Extension Centre
of JNTBGRI, Puthenthope, Thiruvananthapuram were selected as parents based
on variability in floral characteristics and these were evaluated
for various
quantitative and qualitative characters.
Statistical analysis was carried out in Completely Randomized Design and
analysis of variance revealed highly significant differences for all the biometrical
characters included in the evaluation. Estimation of components of variance
revealed that Phenotypic Coefficient of Variation (PCV) was higher than both
Genotypic Coefficient of Variation (GCV) and Environmental Coefficient of
Variation (ECV) for all the traits studied. PCV (143.93) and GCV (128.52) were
the highest for number of spikes plant-1. Heritability was the highest for flower
width (99.06 %) and it was high for all thirteen traits. Genetic advance as percent
of mean was high for all the traits studied. It was the highest for number of spikes
plant-1 (239.80). Estimated phenotypic correlation coefficient revealed highly
significant and positive association between flower length and flower width
(0.9519). The highly significant and negative association was obtained between
internodal length and days for inflorescence emergence to first flower opening
(-0.6896). Similarly genotypic correlation coefficient exhibited highly significant
and positive association between flower length and flower width (0.9545) and
highly significant and negative association between plant spread and number of
leaves plant-1 (-0.9903).
Based on this, parents were selected and were crossed in all possible
combinations. In Vanda a hybrid evolved from the wild species was available at
the centre and it was also crossed with the wild parents to study the cross
compatibility of wild species with hybrids.
In experiment II, cross compatibility of 152 cross combinations made was
studied based on successful capsule setting. Capsule characteristics were
recorded. The genus Spathoglottis took only four days for attaining pod setting
whereas for the genus Rhynchostylis it was ten days for pod setting. Capsule
attained maturity much earlier (30 days) in the genus Spathoglottis but the species
Vanda spathulata took more days for attaining capsule maturity i.e., harvesting
stage (150-154 days).
In experiment III, capsules developed among thirty one cross combinations
were subjected to seed culture for rapid germination under in vitro condition and
seedling development. Observations regarding seed germination were recorded
and seeds of ten crosses exhibited seed greening and initiation of protocorm
development.
Seeds of seven cross namely one intergeneric hybrid and six
interspecific hybrids were developed into seedlings. Evaluation of hybrid
seedlings was made based on variability in morphological characters at monthly
intervals. The six interspecific hybrids were Spathoglottis unguiculata x
Spathoglottis albida (Culture 622), Spathoglottis gracilis
x
Spathoglottis
unguiculata (Culture 652), Spathoglottis albida x Spathoglottis unguiculata
(Culture 778), Spathoglottis albida x Spathoglottis unguiculata (Culture 1368),
Spathoglottis plicata x Spathoglottis unguiculata (Culture 1386), Spathoglottis
unguiculata x Spathoglottis plicata (Culture 1388) and intergeneric hybrid was
Spathoglottis unguiculata x Vanda sp. (Culture 679).
In experiment IV, molecular characterisation of seedlings evolved through
the crossing was done based on ISSR analysis to distinguish F1 hybrid seedlings
from selfed seedlings and their parents. Percentage of polymorphism between
hybrids and parents ranged from 11.99 to 32.97 and these results confirmed that
all the seven crossed seedlings tested were F1 hybrids and these were distinct from
their relevant parents.
The above study revealed that through distant hybridization in wild orchids,
one intergeneric hybrid
Spathoglottis unguiculata x Vanda sp. and six
interspecific hybrids viz., Spathoglottis unguiculata x Spathoglottis albida,
Spathoglottis gracilis x Spathoglottis unguiculata, Spathoglottis albida x
Spathoglottis unguiculata, Spathoglottis albida x Spathoglottis unguiculata,
Spathoglottis plicata x Spathoglottis unguiculata, Spathoglottis unguiculata x
Spathoglottis plicata could be obtained and molecular characterization confirmed
the hybridity of the intergeneric and interspecific hybrids. Therefore, the
intergeneric and six interspecific F1 hybrids evolved through distant hybridization
can be carried forward for the development of varieties or can be utilised for
genetic improvement programme in future.