Effect Of Heat Stress On Panicle Development And Characteristics Of Indica Rice (Oryza Sativa L.)

In recent years, high temperature weather happened frequently at the middle and lower reaches of the Yangtze river in summer, which threathened single-season rice production. The stage of rice flowering is the most sensitive stage to high temperature. So, the measure, delaying the sowing data to avoid high temperature encounting with rice flowering, was taken in rice production, but the measure made the high temperature weather encountered with the period of rice panicle initiation. And, nowdays, high temperature weather has an advance trend obviously because of the intensification of climate change, which increased the possibility of heat stress happened at the period of panicle initiation. At present, lots of study concentrated on heat stress at rice flowering stage rather than at rice panicle initiation stage. So, in this study, two cultivars, with different heat levels which were evaluated in actual production,‘Huanghuazhan’(heat tolerance) and ‘Fengliangyou6’(heat sensitive), were subjected to treatments in artificial climate chambers of heat stress to ascertain the effect of high temperature on panicle initiation, spikelets formation and grain filling.1. Rice panicle initiation stage of two cultivars were divided to four treatment periods according to order of leaf growth order as follows: growth duration of leaf of the fourth to bottom(Ι), growth duration of leaf of the third to bottom(Ⅱ), growth duration of leaf of the second to bottom(Ⅲ), growth duration of last leaf(Ι), and respectively treated in artificial climate chamber of high temperature(40℃) for 7 d in 2014. The resulted indicated that, high temperature reduced the number of spikelets per panicle, the decline degree of high temperature at stage III and IV was larger than at stage I and II due to high temperature accelerated the degeneration of branch and spikelets at III and IV stage. And the ratio of degenerated spikelet was higher in stage IV, which was up to 67%, the ratio of ‘Fengliangyou6’was larger than ‘Huanghuazhan’, caused the phenomenon of ‘white panicle’. And high temperature at IV made worst effects on fertility rate and 1000-grain weight, the reduction of ‘Fengliangyou6’was larger than ‘Huanghuazhan’. The experiment explain the stage of the last leaf growth was the most sensitive stage to heat stress across the rice panicle period.2. The two cultivars were treated in high temperature(40 ℃) when the third leaf to top extracted( branch and spikelets differentiation stage) for 10 d in 2015 to explore the effect of high temperature on panicle initiation. The results shows that high temperature inhibited panicle initiation, shorten the length of the primary branches, and the panicle development days were extended for 2.5d(‘Huanghuazhan’) and 8.8d(‘Fengliangyou6’) respectively, but there was no effect of high temperature on the size of spikelets, heading traits and spike fertility.3. The same two cultivars were treated in artificial climate chambers under High temperature(10:00-15:00, 40℃) and Normal temperature(10:00-15:00, 32℃) for 1, 3, 5, 7, and 9 days at last leaf emergence stage(pollen formation-pollen meiosis stage) in 2015, and the rice grown in ambient was control. The results indicated that,(1) the ratio of spikelet degeneration increased greatly with heat-treating time. The ratio of spikelet degeneration of ‘Huanghuazhan’ increased 45.8% and 62.9% after 9 days under high temperature comparing with normal temperature treatment and CK, and the ratio of ‘Fengliangyou6’ increased 81.7% and 136.1% under the same treatment, the ratio of spikelet degeneration of ‘Fengliangyou6’ was more than ‘Huanghuazhan’.(2) the pollen activity significantly decreased after 1 day under high temperature stress, and anther filling degree significantly decreased after 3 days under high temperature stress. Bad anther formation and pollen activity under high temperature stress was reason that the seed-setting rate decreased significantly.(3) spikelet length and grain filling of two cultivars decreased due to heat stress effect, made a significantly reduction of grain weight, and the reduction rate of ‘Fengliangyou6’ was more than ‘Huanghuazhan’.Grain filling reduced significantly after 5 days high temperature treatment. According to the study, heat stress at last leaf emergence stage may sharply decrease rice yield, cultivation measures should be correspondingly strengthened and improved in practice.4. The same two cultivars were treated in high temperature(40 ℃) when the last leaf extracted( pollen formation-meiosis stage) for 10 d in 2015 to determine effects of hig temperature(40℃) on the rice organ morphology, dry matter accumulation and physiological indexes. The results indicated that, high temperature promoted the top three leaves growth, increased the “Cond” and “Trmmol” of leave, and had on significant effect on the leaf photosynthesis. High temperature shortened the top internode, reduced plant height and heading degree, and also decreased the number of spikelets per panicle. The study also found that high temperature had no effect on dry matter accumulation, but significantly influenced the dry matter distribution, lead high internode branches occur.