Abstract
Low temperature decreases biomass production and yield in rice through a number of physiological and morphological changes. We evaluated biomass production in 22 high-yielding genotypes and four commercial japonica cultivars early after transplanting under field conditions for 2 years. The seedlings were transplanted on 30 April or 1 May (early transplanting, ET) and 4 weeks later (late transplanting, LT). The mean air temperature during the 18 days after transplanting in ET was about 4ºC lower than that in LT in both years. The seedling length was greater in high-yielding japonica varieties than in indica genotypes, whereas the seedling character index (SCI), which is the product of plant age in leaf number and the ratio of the seedling weight to its length, was the highest in the indica genotypes. Varietal differences in biomass production were greater in ET than in LT in all rice genotypes. The biomass at 18 days after transplanting was largest in the japonica high-yielding varieties Kusayutaka and Beko-aoba in both ET and LT. The biomass production of the indica genotypes was found to decrease severely after transplanting at low temperatures although the indica genotypes with high SCIs showed faster leaf emergence than the high-yielding japonica varieties. There was a strong positive correlation between the varietal differences in biomass production and shoot length at 18 days after transplanting in ET in both years. Our study suggests that superior shoot elongation in the high-yielding japonica varieties with large biomass allocation to the stems may be advantageous in maintaining biomass productivity at low temperatures.
