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, post-germination and seedling stages. For each experiment 10 replicates were arranged with 20-40 seeds per replicate. At germination stage, cold stress was applied at 20°C and 15°C and the number of germinated seeds was counted. Post-germination stage cold tolerance was evaluated on 4-day germinated seeds by holding them at 4°C 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 4°C 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 post-germination 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. DOI: http://dx.doi.org/10.4038/tare.v14i2.4838 Tropical Agricultural Research & Extension 14(2): 2011 24-33
Highlights
Cold stress at the seedling stage and high temperatures at flowering stage occur in the regions of subtropics where rice is cultivated
The results showed the suitability of the population for Quantitative Trait Loci (QTL) analysis at germination, post germination and seedling growth stages
The results showed a significant difference in the two cultivars for cold tolerance at the seedling stage from 3 day cold stress onward(Fig.7)
Summary
Cold stress at the seedling stage and high temperatures at flowering stage occur in the regions of subtropics where rice is cultivated. In the temperate regions rice growth is constrained by the limited period that favors growth where it needs optimum temperature between 25oC to 35oC and temperatures below this often result in poor seedling vigor (Reyes et al 2003).Temperatures below 25oC would cause growth abnormalities in temperate and high-elevated tropical rices Development of rice cultivars with considerable level of cold tolerance is needed. Continuous selection for high yield can result in the narrowing down of gene pool while it reaches a yield plateau. One way of overcoming this problem is to introgress Indica and Japonica gene pools (Dilday 1990)
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