PhD

A study was undertaken in the Department of Plant Breeding & Genetics of
College of Horticulture, Vellanikkara, during 1993-2000 entitled "Genetic analysis
in horsegram (Dolichos biflorus Lin.) with special reference to photoperiodic
response" The main objectives were to identify stable, high-yielding, day-neutral
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horsegram genotypes suitable for year-round cultivation and to understand the nature
of gene action involved in the inheritance of photoperiodic response in the crop.
The material consisted of 115 horsegram genotypes. Evaluation of the
genotypes during rabi (traditional)indicated that enough variability exists among the
genotypes with respect to seed yield and yield attributes. Studies on correlation and
cause-effect relations among seed yield and yield attributes revealed that pod yield,
. harvest index and haulms yield were the traits having maximum positive association
and positive direct effect on seed yield. Duration to flowering or maturity did not
have significant correlation with seed yield. Hence it is possible to have varieties that
combine high yield and early maturity. Based on genetic diversity, the 115 genotypes
were grouped into ten clusters, using Mahalanobis D2 statistics. It was found that
genetic diversity existing among genotypes is not associated with their geographical
origin. A selection index constructed based on seed yield, pod yield and harvest
index was found to give 79.47 per cent gain in efficiency over selection based on
yield alone.
Genotypes selected on the basis of the preliminary evaluation were further
tested over two seasons (rabi and summer) for three years (1997,1998 and 1999) in a
comparative yield trial, to select best genotypes suitable for each seasons. The study
revealed that the day-neutral genotype AK-42, is ideal for year-round cultivation.
However, for cultivation during rabi, the photosensitive variety PHG-9 was found to

be better. In general, performance of genotypes was better during rabi than III
summer.
Hybridisation studies between day-neutral and photosensitive types, also was
taken up in order to assess the combining ability and gene action involved and for
estimation of heterosis. The diallel analysis revealed that the parents AK-42 and AK-
26 (both day-neutral types ) had maximum positive general combining ability for
seed yield. Highest specific combining ability for the trait was observed for the cross
PHML-64 x AK-42. Relative heterosis also was observed to maximum for the same
cross. Higher gca expressed by traits like days to flowering, seeds per pod and pod
length indicated that these traits are controlled by additive gene action. Higher sea
was observed for plant height, hundred seed weight, seed yield and pod yield,
indicating that non-additive gene action play a major role in expression of these
traits.
The results of F2 evaluation revealed that photoperiodic response in
horsegram is probably a qualitative trait, controlled by at least two genes, either in
complimentary gene action or inhibitory gene action. In the case of inheritance of
seed colour, the black seed colour was observed to be dominant over brown. Two
genes in polymeric gene action, were found to control seed colour.