PhD

The research project 'Genetic Analysis of High Yielding Rice
Varieties of Diverse Origin' was carried out in the College of. Horticulture,
Kerala Agricultural University, Vellanikkara, Thrissur during the period
1995-'98. The major objectives of the study were to understand the
genetic architecture of high yielding rice varieties of diverse origin so as to
evolve appropriate breeding methodology, to isolate promising lines having
the new ideotype concepts from the segregating generations and to identify
alternative source of cytoplasmic male sterile system suitable to warm
humid climatic conditions experienced in Kerala.
The study, about components of heritable variation revealed that the
characters, number of panicles m-2 number of tertiary branches panicle-1,
yield ha-1, spikelet sterility percentage and alkali spreading value exhibited
high broad sense heritability coupled with high expected genetic advance
and high genotypic coefficient of variation. High broad sense heritability
and high expected genetic advance coupled with moderate genotypic
coefficient of variation were manifested by the characters, namely, height
of plant at harvest, second uppermost internodal length, length of flag leaf,
ratio of vegetative phase to reproductive phase, number of spikelets
panicle-1 number of grains panicle-1, LIB ratio of grain, milling percentage,
amylose content, volume expansion ratio and water uptake.
'1

Correlation studies revealed that the principal yield determining
components in rice are harvest index, number of tertiary branches panicle-1
number of panicles m-2 number of grains panicle-1 number of spikelets
panicle-1. ratio of vegetative phase to reproductive phase, 1000 grain
weight, number of days to 50 per cent flowering, number of days to harvest
and spikelet sterility percentage. While selecting genotypes for higher yield
potential, emphasis should be given for comparatively long vegetative
period, short period from panicle initiation to 50 per cent flowering and long
ripening period.
A selection model was formulated consisting of the characters,
namely, yield ha-1 harvest index, number of days to harvest, number of
tertiary branches panicle-1 ratio of vegetative phase to reproductive phase
and number of grains panicle-1
Cluster analysis revealed that there was no parallelism between
geographical distribution and genetic diversity. The 56 genotypes
representing different eco-geographical regions were grouped into nine
clusters based on genetic distances.
Combining ability studies showed that both additive and non-additive
gene effects were important, with predominance of non-additive gene
action, for all the characters except for 1000 grain weight, second
uppermost internodal length and height of plant at harvest.

The varieties Vytilla3, Mahsuri, Mattatriveni and Karthika were
identified as good general combiners.
The varieties Mahsuri, Karthika, Vytilla 3, Mattatriveni and
IR62030-18-2-2 showed pronounced cytoplasmic effect on yield and
various yield contributing characters.
The crosses Vytilla 3 x Mattatriveni, Mahsuri x Vytilla-3 an,d Mahsuri
x Mattatriveni are recommended for recombination breeding. The crosses
Vytilla 3 x IR36, Vytilla 3 x IR60133-184-3-2, PK3355-5-1-4 x Bhadra,
Vytilla 3 x Mattatriveni, Karthika x Bhadra, PK3355-5-1-4 x Karthika and
PK3355-5-1-4 x IR620'30-18-2-2 are recommended for heterosis breeding.
The cytoplasm of Vytilla 3 (an improved saline tolerant variety of
Kerala) was identified as an alternative source for cytoplasmic male sterility
in rice, suitable to warm humid tropical climate, experienced in Kerala. The
varieties IR36 (international check) and Hraswa (extra short duration
high yielding variety of Kerala) are the proposed maintainer lines.
Mattatriveni is the proposed restorer line for the proposed IR36 'A’ line
and Hraswa 'A’ line.
The generation mean analysis using six parameter model revealed that
both additive and non-additive gene effects played an important role in the
inheritance of yield and important yield components, with predominance
of dominance, additive x additive and dominance x dominance type of
gene effects.

Results of inbreeding depression indicated absence of reduction in
vigour in the F2 generations for yield and all other yield attributes.
Investigation on pattern of inheritance of kernel colour revealed that
kernel colour in rice is a complex qualitative character. Each red and white
colour may be separately controlled by two or more sets of genes having
both inhibitory and duplicate type of gene interactions with predominance
of inhibitory type gene interaction.
From 22F2 generations, seven early stabilized promising lines and 26
promising segregants were selected. Two early stabilized lines were found
to possess most of the ideotype features proposed by IRRI with preferable
cooking quality characters. Their further evaluation and multiplication are
being carried out at the Agricultural Research Station, Mannuthy, Kerala
Agricultural University.
By hybridization, it was possible to successfully transfer the non
sticky nature and red kernel colour of Mattatriveni to a high yielding Taiwan
variety whose kernel is white and sticky on cooking.
The gene action studies revealed that there is ample scope for yield
improvement in rice both through pedigree breeding and heterosis breeding.
As yield and yield components were found to be under the control of all the


three types of gene actions namely, additive, dominance and epistasis,
intercrossing of early segregating generations derived from multiple
crosses seems to be the best suited method of breeding for yield
improvement in rice.
Future line of studies suggested
1. Conversion of the already obtained cytoplasmic male sterile F1
crosses to fully sterile CMS lines by repeated back crossing with the
respective recurrent parents.
2. Screening from the segregating populations of these cytoplasmic
male sterile crosses for 100 per cent cytoplasmic male sterile lines.
3. Confirmation of the restoring ability of the proposed Mattatriveni 'R'
line and identification of other restorers.
4. Incorporation of the sterile cytoplasm of Vytilla 3 into other elite
genotypes other than IR36 and Hraswa.
5. Screening for cytoplasmic male sterile system in other saline tolerant
lines.
6. Screening of promising segregants selected, for high yield and quality
with multiple resistance to pest and diseases, for developing varieties
suited to various climatic and soil conditions of Kerala.