Effects of Low Temperature after Flowering on Grain Filling and Plant Hormone Contents in Rice

Four varieties, indica-japonica hybrid rice Yongyou 538 and Yongyou 17, indica rice Zhongzheyou 1 and japonica rice Zhejing 88 were treated under low temperatures in different time periods of grain filling stage, to analyze endogenous hormone changes and differences in different treatments in grain filling process. The results showed that the effects of low temperatures in different time periods after flowering on grain filling showed an order of early stage 〉 middle stage 〉 late stage, while the difference between the effects of lower temperatures on grain filling in middle and late filling stage was not significant, and the effects of low temper- atures on Yangyou 17 and Zhongzheyou 1 were higher than those on Yangyou 538 and Zhejing 88. Low temperature in early filling stage after flowering aignifieanfly slowed grain filling of Yongyou 17 and prolonged filling duration, while the effect on Yongyou 538 was not significant. Under low temperature treatments after flow- ering, changes in endogenous hormone contents in various varieties differed to certain degrees, IAA and ZR contents in grains of Yongyou 17 in early and middle filling stage decreased significantly, while GA3 and ABA contents were improved remarkably ; and Yongyou 538 showed significantly reduced GA3 content in grains, but higher IAA and ZR contents, which were the main reason for normal filling in grains. Proper hormone regulation measures could be taken in production to improve filling of rice grains under low temperature.

Combining QTL mapping and expression profile analysis to identify candidate genes of cold tolerance from Dongxiang common wild rice(Oryza rufipogon Griff.)

Rice（Oryza sativa L.）, a tropical and subtropical crop, is susceptible to low temperature stress during seedling, booting, and flowering stages, which leads to lower grain quality levels and decreasing rice yields. Cold tolerance is affected by multiple genetic factors in rice, and the complex genetic mechanisms associated with chilling stress tolerance remain unclear. Here, we detected seven quantitative trait loci（QTLs） for cold tolerance at booting stage and identified one cold tolerant line, SIL157, in an introgression line population derived from a cross between the indica variety Guichao 2, as the recipient, and Dongxiang common wild rice, as the donor. When compared with Guichao 2, SIL157 showed a stronger cold tolerance during different growth stages. Through an integrated strategy that combined QTL-mapping with expression profile analysis, six candidate genes, which were up-regulated under chilling stress at the seedling and booting developmental stages, were studied. The results may help in understanding cold tolerance mechanisms and in using beneficial alleles from wild rice to improve the cold tolerance of rice cultivars through molecular marker-assisted selection.