Abstract:
Indica rice cultivar Hokuriku142, japonica rice cultivar Hyogokithanishiki and a recombinant inbred
line population involving these cultivars were evaluated for cold tolerance at germination, postgermination and seedling stages. For each experiment 10 replicates were arranged with 20-40 seeds per
replicate. At germination stage, cold stress was applied at 20oC and 15oC and the number of germinated
seeds was counted. Post-germination stage cold tolerance was evaluated on 4-day germinated seeds
byholding them at 4oC for 1-12 days and gained hypocotyl length was measured after a 4-day recovery
period at normal growth conditions. To assess the seedling stage cold tolerance 1-week-old seedlings
were maintained at 4oC for 1-7 days and green plant height was measured after a 5-day recovery
period. In all growth stages Hyogokithanishiki showed higher degree of cold tolerance than Hokuriku.
Recombinant inbred line population showed normal distribution curves for germination and postgermination stage cold tolearance with transgressive segregants for both higher and lower levels than
the parents. At the seedling stage, the inbred populations showed a skew towards the susceptible
cultivar but there were two transgressive segregants for greater cold tolerance than Hyogokithanishiki.
Identification of such significant differences in the two parental rice cultivars and distribution of the
character across the range of different tolerance levels with transgressive segregation indicates that this
population is useful for the development of cold tolerant rice cultivars and to understand the basis of
the cold regulation of rice using molecular tools.
