PhD

Investigations to identify stable male sterile lines and better combiners
for the exploitation of hybrid vigour in rice were conducted at College of
Horticulture, Vetlantkkara and at Agricultural Research Station, Mannuthy
during 1994-98. The study included evaluation of cytoplasmic - genic male
sterile (CMS) lines to identify stable lines, identification of maintainers and
restorers for different CMS lines, inheritance of fertility restoration, studies
on the genetic distance between maintainers and restorers and genetic
analysis of the hybrids.
Out of the ten CMS lines evaluated, seven were identified as stable
for pollen and spikelet sterility behaviour. Studies on the floral traits which
influence outcrossing expressed variation between CMS lines and between
seasons.
Jyothi, Aruna, Pavizham and Ptb 10 produced more number of sterile
hybrids when crossed with CMS lines having WA cytoplasm and hence
these varieties can be used as maintainers. More number of fertile hybrid
combinations were produced by Annapoorna, Matta Triveni, Kanchana, IR
36 and Aiswarya indicating the use of these varieties as restorers for WA
cytoplasmic source.
All the genotypes under study produced sterile hybrids when crossed
with CMS lines having O. perennis cytoplasm and no restorers could be
identified for this new source of cytoplasmic male sterility.
Inheritance studies on fertility restoration indicated polygenic mode
of inheritance for this particular character.



Forty four rice genotypes included in the hybrid rice breeding
programme were grouped into nine clusters, each having different number
of genotypes. Maintainers and restorers were distributed in different
clusters and no direct relation could be established between heterosis and
genetic distance of the parents.
Genetic analysis of the 34 fertile hybrids resulted in the identification
of five hybrids having significant positive standard heterosis. Among the
male sterile lines IR 68890A was identified as the best combiner for most
of the agronomic traits and IR 68890A/Aiswarya was the best specific
hybrid combination.
Magnitude of the gca variance was more than the variance due to sca
for days to flowering, total duration, harvest index, 100 seed weight and
other grain characters indicating predominance of additive variance for these
characters. Variance due to sca was more for plant height, tillers per plant,
total dry matter production, grain yield per plant, straw yield per plant,
panicle length and filled grains per panicle indicating predornlnance of
variance due to dominance and epistasis.
Studies on association of characters in hybrids revealed that total
drymatter accumulation, harvest index, number of filled grains per panicle,
grain breadth, panicle weight, grain density, flag leaf area and leaf area
index at 60 days after sowing were positively correlated with grain yield
produced by the hybrids.
Negative influence of sterile cytoplasm was identified for most of the
agronomic attributes.