Effects of High Temperature Stress during Meiosis Stage on Dry Matter Partitioning and Yield Formation in Rice.

To quantify the effects of heat stress during meiosis stage on dry matter partitioning and yield formation, two japonica rice cultivars Nanjing41 (NJ41) and Wuyunjing24 (WYJ24) with the characteristic of different heat stress tolerances, were evaluated in this study. Four temperature regimes (Tmax/Tmin were 44/34℃ (T4), 40/30℃ (T3), 36/26℃ (T2), and 32/22℃ (T1) and three temperature durations (2 days (D1), 4 days (D2) and 6 days (D3)) for each temperature regime were set in phytotron. The results indicated that dry matter partitioning index of panicle decreased while those of leaf and stem increased after anthesis with the increase of temperature levels and high temperature durations. Compared with T1 (CK), grain number and grain weight decreased under treatments of T2, T3D1 and T3D2, which resulted in decreasing yield, while no significant changes was observed on setting rate and effective panicle number. Due to lower grain number, seed setting rate and grain mass, yields decreased in T3D3 and T4. However, yield losses in T3D3 and T4 were compensated to some extent (about 20%) with increasing effective spike number on regeneration tillers. The effect of high temperature on grain weight was represented as upper part > middle part > lower part. There was significant effect of T4 on setting rate of each panicle part on NJ41 while there was no effect of T4D1 on WYJ24. Therefore, NJ41 was more sensitive to extreme high temperature levels. However, WYJ24 was affected by high temperature duration more seriously since the effect of T3D3, T4D2 and T4D3 on setting rate was much more significant than NJ41. In T4D3, regenerated tillers compensated setting rate loss of primary tillers in NJ41. Some of the regenerated tillers of WYJ24 were not filled till harvest, thus compensation effect was less than NJ41. Effect of level and duration of high temperature on setting rate and grain weight was quantified by Heat Degree Days (HDD). Setting rate and grain weight decreased linearly with increasing HDD. Semi lethal (50% setting rate) HDD in WYJ24 was higher than NJ41.These results could provide theoretical support for management and regulation under heat stress during meiosis stage.