Abstract
Poor spikelet fertility under low temperature (LT) stress during anthesis limits the possibility of high yield potential in indica–japonica hybrid rice, leading to reduced stability of grain yield. However, the cause for it is still unclear. In this study, three indica–japonica hybrid rice cultivars, Yongyou9, Yongyou17 (both cold sensitive), and Yongyou538, and one japonica inbred rice cultivar, Zhejing88 (cold tolerant), were grown under LT (17°C) and ambient temperature (AT) (25°C) during anthesis to test for their response with respect to spikelet fertility, pollen germination, and spikelet flowering. The results indicated that LT resulted in lower spikelet fertility in cold-sensitive cultivars than in cold-tolerant cultivars. Spikelet fertility was highly correlated with pollen germination on the stigma. The number of pollen grains and germinated pollen were higher in cold-tolerant cultivars than in cold-sensitive cultivars. Pollen fertility and pollen diameter were also higher in cold-tolerant cultivars, although the latter could achieve a high number of spikelets at anthesis in flowering patterns throughout the duration of LT stress. There were significant differences in anther width and volume between genotypes and treatments according to microscopic analyses, but no differences were observed in anther dehiscence. Moreover, variation in the number of pollen grains on stigmas and in spikelet fertility was not related to either the number of spikelets reaching anthesis or anther dehiscence. Overall, improved anther size, better pollen function, and higher spikelet fertility under LT stress were observed in cold-tolerant cultivars than in cold-sensitive cultivars. The results suggest that the increase in spikelet fertility is due to enhanced pollen germination rather than the number of spikelets reaching anthesis.
Highlights
Rice (Oryza sativa L.) is a staple grain crop
Elongation of panicle exsertion significantly decreased (P < 0.05) among cultivars subjected to low temperature (LT) stress compared with ambient temperature (AT) (Table 2)
peduncle length (PeL) among the cultivars was consistently maintained in response to LT stress and was 68.1% longer in cold-sensitive cultivars than in cold-tolerant cultivars
Summary
Rice (Oryza sativa L.) is a staple grain crop. Six hundred million tons of rice are produced annually, and rice is widely cultivated throughout the world (IRRI, 2002). The mean critical temperature for rice is +4.7◦C, and once the ambient temperature (AT) is Chilling-Stress Affects Rice Spikelets Development below 5–10◦C, irreversible LT-induced damage to seedling growth and development can occur (Sanchez et al, 2014). Farrell et al (2001, 2006) reported that rice was susceptible to abundant LT-induced damage during the young microspore stage, and 12 h of exposure to LT can cause spikelet sterility. LT-induced spikelet sterility during the microsporogenesis stage is considered genotype dependent, which for cold-tolerant genotypes was a night-time air temperature of 15◦C for 4 consecutive days and for cold-sensitive genotypes was a night-time air temperature between 17 and 19◦C (Satake, 1969). Developing and verifying cold-tolerant cultivars will be beneficial for overcoming the influence of LT stress on rice growth and development
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