PhD

The research project "Exploitation of male sterility in
sesame (S.indiclll1l L.)" was carried out in the college of Horticulture,
Kerala Agricultural -University, Vellanikkara during 1996-'99. The
persent investigation was carried out with a view to assess the
variability and to estimate 'the combining ability of selected lines.
Exploitation of male sterility in sesame through induced mutagenesis
and wide hybridization for future development of hybrid sesame was
also aimed at.
Sixty genotypes of diverse origin were evaluated during
'96-'99 at Onattukara Regional Agricultural Research Station,
Kayamkulam for their divergence using Mahalanobis D2 statistics.
Based on yield and attributed components, these genotypes were
grouped into eight clusters. Eight genotypes representing each cluster
were selected and were evaluated for their combining ability, gene acton
and heterosis using diallel analysis. Two best general combiners were
selected and carried forward for the induction of male sterility through
mutagenesis and wide hybridization.
The wide range of variation was noticed in all the ten
characters among the 60 genotypes selected for divergence study
indicates the presence of substantial genetic _ variability among the
genotypes. The magnitude of heterosis was largely dependent on the
degree of genetic diversity in the parental lines.
The study on genetic parameters revealed that the
characters number of branches per plant, number of capsules per main

stem and seed yield per plant exhibited high broad sense heritability
coupled with high expected genetic advance along with high or
moderate GCV.
Correlation studies revealed that the principal yield
determining components were capsules per main stem and capsules per
plant. While selecting genotypes for higher yield potential, emphasis
should be given for these characters. Cluster analysis revealed that there
was no parallelism between geographical distribution and genetic
diversity of the genotypes. The sixty genotypes representing different
geographical regions were grouped into eight clusters based on genetic
distances.
Combining ability studies revealed the importance of all
the three additive, non-additive and maternal effects in all the characters
studied. The varieties Thilak and OS-2 were identified as best general
combiners.
Studies on induced mutagenesis clearly indicated that
both physical as well as chemical mutagens reduced the germination,
survival and fertility in the M] population. A linear increase in the
sterility with increase in the doses of mutagens was noted. Chemical
mutagens were found to induce more number of steriles than the physical
mutagens. Male sterile types isolated were similar in habit as the normal
plants but for their shrunken, green undersized anthers. These plants
had normal female fertility and exihibited regular seed set. Inheritance
studies indicated that the present case of male sterility is governed by a
single recessive gene.

In the wide hybridization of Sesamum in dicum x
S.malabaricum, F I S had high percentage of pollen fertility as indicated
by a fairly good capsule set on selfing while reciprocals had little
capsule set on selfing. This points to a positive role of the wild
cytoplasm on the expression of sterility in crosses where
S. malabaricum was used as female parent. The F I interspecific hybrids
both direct and reciprocal, exihibited dominance of the wild parent
characters in hybrids. Progenies of back crosses BCI and BC2 exihibited
more of the attributes of the recurrent parent indicating further
improvement of hybrids for desirable attributes retaining high levels of
male sterility along with. These lines offer scope for efficient utilization
in future hybrid seed production programme in cultivated sesame.