The gene action for cold tolerance in rice (Oryza satiWl L.) cultivars was investigated In
three sets of half diallel crosses, viz., a 5 x 5 Indica x Indica (I x I) set, a 5 x 5 japonlca
x japonica (J x J) set, and a 7 x 7 indica x japonica (I x J) set. Minimum temperature
for chloroplast biogenesis (MTCB) and spikelet fertility depression coefficient (FDC) were
used for evaluating cold tolerance at the vegetative and reproductive phases, respectively.
Whereas in the I x I set, general combining ability (gca) variance was predominant, In
the J x J set the specific combining ability (sea) variance was more prevalent. In the I x
.J set, both effects were of similar magnitude, Indicating japonlca cultivars as primary
source of nonadditive effects. The covariance-variance (Wr-Vr) graph Indicated that
japonica cultivars had dominant genes for MTCB but recessive genes of FDC. As these
cultivars were cold tolerant at both vegetative and reproductive phases, the reversal of
gene action appears to be due to Involvement of two different traits evaluated at two
different growth phases, rather than reversal in gene action for cold tolerance per se.
Persistent heterogeneity of Wr-Vr over the arrays In noninteractlng I x J set for MTCB
and FDC and in I x I set for FDC Indicates Involvement of multiple alleles In the control
of cold tolerance. In view of this, an appropriate breeding strategy has been proposed.
Keywords: Cold tolerance, diallel analysis, multiple alleles, chloroplast biogenesis, fertility depression.
Article DOI: NA
Print ISSN: 0019-5200
Online ISSN: 0975-6906
M. K. MAJUMDER, D. V. SESHU AND V. V. SHENOY info_circle