Abstract: Two experimental glass-houses were utilized to study the effects of nighttime temperature increase (NTI) at different growth stages on the grain yield
 of double season rice. The NTI from the stage of sowing to panicle differentiation (primary branch differentiation) improved the tillering of rice, and increased the effective panicles. An average 1 ℃ rise in the minimum nighttime temperature (MNT) at this stage increased the grain yield of early and late rice by 10.02%-13.18% and 6.52%-7.78% (P＜0.01), respectively. The NTI from the stage of panicle differentiation to heading (10% panicle heading from flag leaf sheath) promoted the spikelet abortion, and reduced the number of developed spikelet. An average 1 ℃ rise in MNT at this stage decreased the grain yield of early and late rice by 3.76%-6.67% and 3.66%-6.94% (P＜0.01), respectively. NTI from the stage of heading to maturity decreased the filled grain rate of early rice remarkably, but had an opposite effect on late rice. An average 1 ℃ rise in MNT at this stage induced a grain yield loss  by 2.07%-5.61% (P<0.05) and a grain yield gain by 1.63%-2.28% (P＜0.05) for early and late rice, respectively. All the results illustrated that there existed obvious differences in the effects of NTI at different growth stages on the grain yield of double season rice.

Key words: double season rice, nighttime temperature increase, different growth stages, spikelet differentiation and abortion, yield, endophyte, Achnatherum sibiricum, total phenolic, lignin, methyl jasmonate.