Effects of Water Deficits on Panicle Exsertion in Rice (Oryza sativa L.) and Sorghum (Sorghum bicolor (L.) Moench)

[摘要] The effects of water stress on panicle exsertion in rice appear to differ from those in sorghum. Water deficits after floral initiation increased the time to flowering in sorghum, whereas panicle exsertion in rice was considered to be delayed by stress occurring before floral initiation. The objective of this stydy was to examine whether the effects of water deficits on phenology of flowering are really different between these two crops. Rice (Oryza sativa L.) cultivar Koshihikari and grain sorghum (Sorghum bicolor (L.) Moench) hybrid NK129 planted in a 4l (1/5000 a) pot containing sandy loam soil were grown in a vinyl house. Each pot contained either two rice plants or single sorghum plant which received daily irrigation till the start of drought treatment. Irrigation was suspended to impose 10 and 6 grildients of water stress after floral initiation in rice and sorghum respectively. Plants were rewatered after reaching a desired level of stress (Fig. 1). In sorghum, predawn leaf water potential (ΨL) did not change for several days after withholding water (Fig. 3). Thereafter, it declined first slowly and then rapidly. Similar trend was observed in rice, but its ΨL began to decrease much earlier after withholding water and the rate of decrease was greater than in sorghum. Panicle exsertion was delayed in rice due to water stress and was also delayed in sorghum with an exception in plants subjected to 19 and 24 day drought that accelerated panicle exsertion (Fig.4). The time to panicle exsertion increased linerly with decreasing ΨL below some threshold value (the critical ΨL). The critical ΨL differed between the crops; -0.2 MPa in rice and -1.2 MPa in sorghum (Fig. 5). Furthermore, there were considerable scatter in the data in rice : panicle exsertion was delayed by 5 to 6 days when ΨL remained at around -2.3 MPa. However, when delay in the time of panicle exsertion was plotted against water stress duration, most of the differences above noted were removed (Fig. 6). In other words, the identical relationship was obtained for both crops between the delay in panicle exsertion (D-D0) and the water stress duration (T-TC) : D-D0=1.34(T-TC) where D is the time to panicle exsertion in plants droughted after floral initiation, D0 is that is plants without drought, T is the duration of drought and TC is the duration between the initiation of drought and the time when ΨL declined below the critical value. It is therefore concluded that phenology of panicle exsertion in rice and sorghum is similarly affected by water deficits occuring after floral initiation.

[学科分类] 农业科学（综合）