Studies on the low-temperature damage in rice seedlings

The effect of soil moisture at a low temperature on the growth of rice seedlings, several Indica and japonica varieties was investigated. In this experiment, the wet soil plots (WP) (70% of water holding Capacity) and flooded soil plots (FP) were set. The seedlings were kept at a normal temperature (20degreesC) until the third leaf blade was fully emerged and then exposed to 11degreesC for 12 days. After that, they were again grown at a normal temperature. After the exposure to a low temperature, the top dry weight (DW) was higher in WP than in FP, and no difference was observed between Indica and japonica. The root DW, the number of roots, the seminal root length, the number of lateral roots and the bleeding rate were higher in WP than in FP. These tendencies were remarkable in Indica varieties. The superior growth of the seminal root and development of the lateral roots might be responsible for the superior root activities. After the seedlings returned to the normal temperature, the recovery of top DW, root DW, the root number, the bleeding rate and the rooting ability was higher in WP than in FP. Based on these results, it is considered that the higher recovery of root growth and activities of the root in WP compared to FP after returned to the normal temperature might be due to the lesser damage to root growth and activity in WP during the low temperature exposure. Thus, it is considered that the rearing of seedlings under wet soil conditions can reduce the low-temperature damage in seedlings at the nursery period in double cropping of Indica varieties in Hunan Province of China.