PhD

Hybrid rice technology aims to increase the yield potential of rice beyond the
level of high yielding varieties by exploiting the phenomenon of hybrid vigour or
heterosis. It is the only technology available now to break the yield plateau attained in
rice. Commercial production of hybrid rice can be achieved through three line system
of hybrid rice development. Identification of restorers and maintainers for the system
is the initial step in hybrid rice breeding. So the present study entitled “Genotyping of
Rf (Restoring fertility) loci of rice varieties of Kerala using molecular markers” was
undertaken as an initial step for the development of hybrid rice for Kerala with the
objectives to locate restorers and maintainers from Kerala rice varieties using
molecular markers, validation of the restoration of fertility in cross with WA
Cytoplasmic Male Sterile (CMS) lines, study of inheritance pattern of restorer gene
and to locate heterotic combiners from the possible restorers and maintainers.
In the present study twenty one rice varieties were screened with 13 SSR
markers linked to different Rf genes i.e Rf3, Rf4, Rf5, Rf6 and Rf7. Three varieties
had only one Rf gene, seven varieties had two Rf gene, four varieties had three Rf
gene. Rice varieties Remya, Manupriya and Swarnaprabha had four Rf genes and
PTB-9 had all the Rf genes. For identification of maintainers and restorers from
among the 21 rice varieties under study, these lines were crossed with 4 CMS lines
(IR58025A, UPRI95-17A, CRMS31A and CRMS32A). Pollen and spikelet fertility
of the hybrids recorded that Remya, Swarnaprabha, Manupriya, Varsha and Aiswarya
were restorers for CMS line IR58025A, Remya, Jayathi, Annapoorna, Neeraja,
Aiswarya and Pavizham were restorers for UPRI95-17A. Remya, Jayathi,
Swarnaprabha, Kanakom and Neearaja were restorers for CRMS31A and Remya,
Jayathi, Swarnaprabha, Annapoorna, Kanakom, Mattatriveni and Pavizham were
restorers for CRMS32A. Rice variety Remya alone was found to be the restorer for all
four CMS lines. Rice varieties Jyothi, Kanchana and Aruna were identified as
maintainers for IR58025A. Only one variety Kanchana identified as maintainer for
UPRI95-17A. Bharathy, Jyothi, Kanchana and Aruna were identified as maintainers
for CMS line CRMS31A, while Kanchana and Bharathy were identified as
maintainers for CRMS32A. Kanchana alone was found to be the maintainer for all
four CMS lines. In field validation Remya which had 4 Rf genes (Rf3, Rf4, Rf5 and
Rf6) was found to be a restorer for all the lines with WA Cytoplasm studied. All the
restorers identified through field validation had either Rf3 or Rf4 gene which were
reported as the major genes for fertility restoration.
Study of inheritance pattern of restorer gene was analysed in F2 generation of
the crosses between CMS lines and the restorers. It was found that in UPRI95-17A x
Remya, UPRI95-17A x Jayathi, UPRI95-17A x Annapoorna, UPRI95-17A x
Aiswarya and UPRI95-17A x Pavizham the restoration of fertility is governed by 2
dominant gene. Co-segregation of the molecular marker linked to Rf loci and the trait
of restoration of fertility in the segregating population was analysed through Bulk
Segregant Analysis (BSA) and found co-segregation of marker RM1 with Rf3 gene
and marker RM171 with Rf4 gene. This shows that the marker loci and fertility
restoration genesRf3 and Rf4 are tightly linked.
To assess the genetic parameters of the selected twenty one rice varieties they
were grown in completely randomized block design with 2 replications in pots and
observations were taken on 12 metric traits. The study revealed high heritability
coupled with high genetic advance as per cent of mean for Pollen fertility, number of
spikelets/panicle, number of filled grains/panicle, LB ratio, number of grains/panicle
and grain yield/plant. Hence these traits are predominantly under the control of
additive gene action and hence these characters can be improved by selection. Grain
yield per plant recorded a significant positive correlation with total no of tillers,
number of productive tillers per plant, panicle length, number spikelets/panicle,
number of filled grains/panicle, number of filled grains per panicle. Divergence
analysis grouped the rice varieties into eight clusters. Cluster II consisting of
Mattatriveni and cluster VI consisting of Jayathi, Swarnaprabha, Kanakom and
Aiswarya was the farthest.
The hybrid developed from 23 crosses between identified restorers and 4 CMS
lines were evaluated for heterosis and identified promising hybrids were UPRI95-17A
x Aiswarya, UPRI95-17A x Neeraja, UPRI95-17A x Remya and CRMS31A x
Kanakom based on high mean grain yield per plant and high standard heterosis over
standard check Uma.
In order to assess heterosis in different combination of the identified
maintainers and restorers an L x T analysis was done with maintainers as the lines and
restorers as the testers. Perusal of findings indicated that line Jyothi is a good general
combiner as it recorded a high over all GCA status. The hybrid Aruna x Varsha was
the best specific combiner followed by, Jyothi x Pavizham and Kanchana x
Mattatriveni. Three crosses viz; Aruna x Varsha, Jyothi x Pavizham and Bharathy x
Annapoorna registered high significant heterosis for grain yield per plant over mid
parent, better parent and standard check Uma.
The present study could identify restorers and maintainers for 4 CMS lines
from the Kerala rice varieties and also heterotic combination of restorers and
maintainers. By reconstituting the identified maintainer with sterile cytoplasm of the
CMS lines heterotic hybrids with grain qualities specific to Kerala can be developed.
The superior hybrids obtained from identified restorers and CMS lines can be directly
used for commercial release after yield trial.