Effects Of Temperature And Control Measures During Grain Filling Stage On Fragrance And Quality Of Aromatic Rice

Temperature is the most important climatic factor affecting rice production.The objective of this study was to investigate the effects of temperature during grain filling stage on 2-acetyl-1-pyrroline?2-AP?formation,quality and yield of aromatic rice,to explore the operation effects of temperature comtrol measures,such as planting season,irrigation and spraying,on 2-AP formation,quality and yield of aromatic rice,and to provide theoretical basis for expanding the rational distribution of the production of aromatic rice and increasing the fragrance cultivation of aromatic rice in China.The three experiments were conducted at South China Agricultural University's College of Agriculture,Teaching and Experimental Farm as following.Experiment 1,the pot experiments were carried out using Indica scented rice cultivars Basmati 385 and Xiangyaxiangzhan as planting materials.Temperature treatment were accurately controlled everyday by artificial climatic incubator during grain filling stage:high temperature?HT?for day at 12h 32?,night at 12h 26?,middle temperature?MT?for day at 12h 27?,night at 12h 21?,low temperature?LT?for day at 12h 22?,night at 12h 16?.The effects of temperature during grain filling stage on 2-AP content in grains,leaves and stem-sheaths of aromatic rice were studied,besides,the effects of temperature during grain filling stage on proline dehydrogenase,pyrroline-5-carboxylate synthetase and Ornithine aminotransferase activities,and proline,pyrroline-5-carboxylate and 1-pyrroline contents in grains,leaves stem-sheaths and roots of aromatic rice were investigated,as well as the effect of temperature during grain filling stage on quality and yield in aromatic rice were studied.Experiment 2,the pot experiments were carried out using Indica scented rice cultivars Basmati 385,Meixiangzhan and Xiangyaxiangzhan as planting materials.Planting season treatment were conducted by early season?ES,was sowed at 12/3/2016?,middle season?MS,was sowed at 12/5/2016?,late season?LS,was sowed at 12/7/2016?.The effects of different planting season on canopy temperature and 2-AP content in grains,leaves and stem-sheaths of aromatic rice during grain filling stage were studied,besides,the effects of planting season on proline dehydrogenase,pyrroline-5-carboxylate synthetase,Ornithine aminotransferase activities,and proline,pyrroline-5-carboxylate,1-pyrroline contents in grains,leaves,stem-sheaths and roots of aromatic rice during grain filling stage were investigated,as well as,the effect of planting season on quality and yield in aromatic rice during grain filling stage were studied.Experiment 3,the field experiments were carried out using a scented rice cultivar Yuxiangyouzhan as planting materials in early March?regarded as early season rice?in both 2014-15.In this study we assessed different short-term water management strategies to cope with the high temperature?average air temperature was more than 33??at early filling stage in aromatic rice.Water was applied as flood irrigation at two various depths i.e.,4-5 cm?I1?and 5-10 cm?I2?during 9:00-18:00 and then drained off at 18:00 as well as applied over-head during different time spans i.e,over-head sprinkle irrigation during 11:00-12:00?S1?,13:00-14:00?S2?and 15:00-16:00?S3?at 60-80%relative humidity?RH?at early filling stage.A control?CK?was maintained with the maintenance of 1cm water layer as normal farmer practice of this region.The effectiveness of different short-term water management strategies were measured by estimating 2-AP content in brown rice,pyrroline-5-carboxylate content,proline dehydrogenase activities,pyrroline-5-carboxylate synthetase activities,ornithine aminotransferase activities in leaves,as well as physio-biochemical responses,photosynthesis,yield and quality of aromatic rice exposed to high temperature stress at early filling stage.The main results are as follows:?1?LT during grain filling stage was conducive to accumulation of 2-AP content in grains of aromatic rice,HT strikingly reduced the 2-AP content in grains of aromatic rice.The 2-AP content of two aromatic cultivar treated by LT was 141.75 and 139.31?g·kg^-1·FW,by HT was 34.51 and 23.10?g·kg^-1·FW,respectively.LT during grain filling stage was conducive to higher activity of proline dehydrogenase,pyrroline-5-carboxylate synthetase and ornithine aminotransferase,and more accumulation of proline,pyrroline-5-carboxylate and 1-pyrroline in grains,leaves,stem-sheats and roots of aromatic rice,then improved 2-AP content of grains,HT was on the contrary.Moreover,HT significantly reduced the yield of Basmati 385 than MT,and LT had no significant differences effect on yield with other temperature.?2?The average canopy air temperature at LS grain filling stage was 24.69?,and day highest/lowest temperature,panicle leaves stems temperature at LS was lower than ES and MS,the average canopy air temperature at ES grain filling stage was 29.91?higher than LS.LSwasconduciveforhigheractivityof proline dehydrogenase,pyrroline-5-carboxylate synthetase and ornithine aminotransferase,and more accumulation of proline,pyrroline-5-carboxylate and 1-pyrroline in grains,leaves and stem-sheats of aromatic rice,then higher 2-AP content in grains during grain filling stage.Moreover the rice quality and yield was higher at LS than ES or MS.?3?Rice early filling stage was easier encountered high temperature at early season,and that could cause a substantial reduction in yield,quality and fragrance of aromatic rice.The short-term water management strategies all could maintain/improve the yield and quality,as well as increase the 2-AP content in grains,inside,S1 treatment had the best comprehensive result.Spraying treatment mainly increased the activity of proline dehydrogenase,pyrroline-5-carboxylate synthetase and Ornithine aminotransferase in leaves,then improved the content of pyrroline-5-carboxylate in leaves,at last significantly improved 2-AP content in brown rice.The 2-AP content treated by S1 was significantly increased of 66.33%and 65.29%respectively in 2014 and 2015 than CK.Moreover,water treatments reduced malondialdehyde?MDA?also regulated the activities of superoxide dismutase?SOD?,peroxidase?POD?,catalase?CAT?,nevertheless,improved plant photosynthesis and gas exchange,rice yield and quality attributes considerably by lowering severity of canopy temperatures than control?CK?.Besides,yield treated by S1 was significantly increased of 23.87%and 34.03%respectively in 2014 and 2015 than CK.S1?over-head sprinkle irrigation during 11:00-12:00?would be the best temperature control measures to cope the high temperature during early filling stage for aromatic rice.