| Pot experiments were employed to study the responses of two indica rice varieties, Zhong 9 B and Jinzao 47, to 4 different soil water supply levels under two climatological chamber conditions and one greenhouse condition with three replications. Leaf water potential (LWP) of two rice varieties at different growth stages were systemically measured with 3rd fully expanded leaf at all time. In addition, the relationship between LWP and the water soil contents, the rice yield and the structure of panicle and the starch quality of rice grain under different water soil supply levels were also investigated. The results showed as follows:1. The diurnal changes of LWP of rice at tillering stage under different soil water treatments tended to be slightly higher at earlier morning and later afternoon, but lower around the midday time, displaying a curve of parabola with a turn around midday time. LWP of rice decreased with the drought stress increasing, however, there were no marked differences between submerged irrigation condition and moisture irrigation condition. In addition, with the water deficit increased, there existed marked differences of LWP of rice between the moisture irrigation condition and the water stress condition. LWP of rice also declined as the advance of growth, indicating that leaf aging index of rice increased as the plant growing.2. LWP is recognized as an index for whole plant water status and considered to be associated with drought resistance, and positive correlations between LWP and soil water contents measured at tillering stage were identified. However, the equation based on a range of soil bulk water contents within 53.03 % ~27.5 % and LWP within -1.0~-2.0MPa and there were no markable differences between rice materials investigated.3. The critical value of LWP of two rice materials at dawn was identified at heading stage about -1.25～-1.32 MPa in terms of the relationship of LWP and water soil contents, and the corresponding water soil contents was 35 % ~40%. There also had a tendency that the critical value of LWP decreased as the rice growth developed, and the differencebetween two rice materials was not significant.4. According to the lowest point of LWP appeared around midday time, the critical value of LWP also could obtain at that time. Anyway, when LWP were less than about -1.60 MPa, -1.70 MPa and -1.80 MPa at tillering stage, booting stage and heading stage around midday time respectively, there might be an adumbration of water deficit appearance in both tested rice materials.5. Two rice varieties responded differently to the decrease of the yield under water stress. The plant height of two rice materials under both climatological chamber condition and greenhouse condition decreased as the water soil contents declined. The significant decrease of yield of rice material Zhong 9 B under three environmental treatments at 60% and 40% soil water treatments were mainly caused by the decrease of effective numbers of panicles. However, rather than the significant decrease of effective numbers of panicles causing the significant decrease of yield of another rice material Jinzao 47, the panicle becoming smaller, total numbers of per panicle and the setting number of panicle turning to lower were the very reason caused the significant decrease of rice yield. The different responses of rice materials to water stress in rice yield reflected the genotype differences of rice materials to water stress.6. The effects of water supply levels on the starch quality were investigated. The apparent amylose content and setback viscosity was increased with the decline of water supply level, whereas the peak viscosity, hot paste viscosity, cool paste viscosity and breakdown viscosity decreased with the decline of the water supply level. It seemed that different water supply level had no effect on gel texture parameters. Although the starch quality parameters reported in this study showed that the eating quality of the rice become poorer, these rice could be used as other processing purpose.
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