PhD

Vigna belonging to the family Leguminoseae is a large genus comprising of
seven sub-genera and over 150 species. The two sub-genera Vigna and Ceratotropis
contain the most important cultivated species. The taxonomical identification of many
of these species is still confusing. The closely related wild species serve as a source of
many desirable genes that can be utilised in the interspecific hybridisation programmes.
This is possible only when the relationships among the different Vigna species are well
understood.
In this context, the present study “Characterisation and systematic evaluation of
genetic resources of the genus Vigna” was undertaken in the Department of Plant
Breeding and Genetics, College of Horticulture at Vellanikkara. Investigations were
undertaken to characterise the accessions of Vigna germplasm available at National
Bureau of Plant Genetic Resources (NBPGR) Regional Station, Vellanikkara, Thrissur
using morphological markers and
to confirm the results using biochemical and
molecular markers in distinct variants belonging to different taxa as well as to prepare a
key for the identification of different Vigna taxa.
The 150 accessions available at NBPGR Regional Station, Vellanikkara were
subjected to morphological, biochemical and molecular characterisation. For
morphological characterisation 48 qualitative and 24 quantitative characters were taken.
The biochemical characterisation of the selected distinct variants from each taxa was done by isozymes, peroxidase and poly-phenol oxidase. The molecular characterisation
was done with Inter Sequence Repeat Analysis using 10 different primers. The
clustering patterns based on all three characterisation were compared and key for
identification of different taxa of Vigna was developed.
Among the qualitative characters evaluated, type of seed germination, nature of
attachment of primary leaves, size of stipule, shape of stipule, presence of ligule, shape
of bracteole, nature of pod attachment to peduncle, curvature of pod, shape of seed and
shape of hilum were distinct for each taxa. Variability was observed in size and shape of stipules and bracteoles. Based on the qualitative characters the 150 accessions were
reclassified into 22 taxa. One accession originally classified as V.radiata var.sublobata
was found to be distinct taxa of Vigna and hence regrouped as distinct taxa. All the 24
quantitative characters studied exhibited wide range of variability. The keel pocket was
present in all taxa except V.unguiculata, V.marina and V.pilosa. The length of keel
pocket also varied from taxa to taxa.
Cluster analysis based on qualitative, quantitative, biochemical and molecular characters resulted in 10, 5, 4 and 12 clusters respectively. A statistical methodology
was worked out to compare the parallelism among the different clustering patterns. The
result showed that there existed a similarity between clusters formed based on
quantitative and qualitative characters, with majority of accessions of each taxa in a
qualitative cluster falling in the same quantitative cluster. The accessions taken for
isozyme and molecular study were distinct. Accessions of same taxa which fell in same
clusters based on isozyme and molecular markers fell in different clusters based on
quantitative characters and vice-versa, indicating the differences and similarities among
these accessions at isozyme and molecular level. Key quantitative characters were also
identified for each taxa based on weighted average.
Based on morphological, biochemical and molecular characters, a dichotomous key was developed to identify different taxa. The key that is now proposed is different
from the existing one which is based on floral and fruit characters alone.