灌浆结实期低温弱光复合胁迫对稻米品质的影响

近年来,南方水稻抽穗灌浆期低温寡照天气发生频率明显增加,为探明其对稻米品质的影响,在水稻灌浆结实期不同时间段(1~7d、8~14d、15~21d、22~28d、29~35d)设置低温弱光复合胁迫(LW)、单一弱光(WN)、单一低温处理(LN)和常温常光(NN)4个处理,研究低温弱光复合胁迫对稻米加工品质、外观品质、蒸煮食味品质、RVA谱特征值等的影响。结果表明,不同处理方式间的垩白米率、垩白大小和垩白度均表现为LW>LN>WN>NN,且灌浆结实期各阶段的复合胁迫均较对照NN差异极显著或显著,除了2016年灌浆结实1~7d的垩白度外,灌浆结实21d内的复合胁迫与单一弱光、低温差异也显著或极显著,单一胁迫低温、弱光在灌浆结实21d内较对照NN差异极显著或显著,其中单一低温与弱光在部分处理下差异达显著水平,灌浆结实21d后,复合胁迫与单一弱光、低温部分差异显著,弱光与低温无显著差异。不同处理间的糙米率、精米率和整精米率均表现为NN>WN>LN>LW,其中,灌浆结实21d内,复合胁迫及单一低温、弱光较对照NN差异极显著或显著,灌浆结实21d后,部分时间段差异显著或极显著。低温弱光复合胁迫及单一胁迫对加工品质影响程度按大小依次为整精米率、精米率、糙米率,且灌浆结实21d内处理的影响大。对蒸煮食味品质,低温弱光复合胁迫极显著或显著降低了稻米的直链淀粉含量、胶稠度、外观、黏度和食味值,显著或极显著提高了蛋白质含量和硬度,单一胁迫低温、弱光表现与复合胁迫相同的影响,且灌浆结实21d内,除2016年的胶稠度,单一低温、弱光较对照NN差异显著或极显著,单一低温、弱光较复合胁迫差异也多显著或极显著。从水稻RVA谱特征值来看,低温弱光复合胁迫及单一胁迫造成稻米的峰值黏度、热浆黏度与崩解值下降,最高黏度、消减值与峰值时间上升,除灌浆结实29~35d的崩解值外,复合胁迫较对照NN差异达极显著或显著水平,部分指标的低温、弱光较对照NN差异也达显著水平。总之,灌浆结实期各时间段的低温弱光复合胁迫及单一胁迫造成稻米品质不同程度下降,且以灌浆结实21d内复合胁迫的影响较大。

Combined effects of low temperature and weak light at grain-filling stage on rice grain quality

In recent years, the low temperature and less sunshine occurred frequently during the heading and filling stages of rice in southern China, which affected rice quality. An experiment was conducted with four treatments including low temperature and weak light combined stress (LW), low temperature under normal light (LN), weak light under normal temperature (WN) and normal temperature under normal light (NN) in five periods of grain filling stage (1-7 d, 8-14 d, 15-21 d, 22-28 d, 29-35 d) to research the influences of low temperature and weak light combined stress on rice quality. The chalkiness rate (CR), chalkiness size (CS) and chalkiness degree (CD) among different stress treatments in each period all showed a trend of LW > LN > WN > NN, in which LW in each setting period of grain filling stage was significantly or very significantly different from NN, in each period within 21 days of grain filling stage, LW was also significantly or very significantly different from WN and LN, and single stress was also significantly or very significantly different from NN, except the whiteness in the period of 1-7 d of grain filling stage in 2016. And in each period within 21 days of grain filling stage, there were no significant difference between WN and LN, of which each was significantly different from LW in some periods. The brown rice rate, milled rice rate and head milled rice rate of different stress treatments in each period reflected NN > WN > LN > LW, in which LW, LN, and WN were all significantly or very significantly different from NN in each period within 21 days of grain filling stage and in some periods after 21 days of grain filling stage. Head milled rice rate was affected more deeply than brown rice rate and milled rice rate by the combined stress or single stress, especially at the periods within 21 days of grain filling stage. LW reduced the amylose, gel consistency, appearance, viscosity and taste value of rice significantly or very significantly and increased protein content and hardness significantly or very significantly; WN and LN showed the same influence trend as LW. LW reduced the peak viscosity, trough viscosity and break down of rice significantly except the breakdown of 29-35 d of grain filling stage, and increased final viscosity, set back and peak time significantly too. In general, low temperature and weak light combined stress and single stress deteriorate the rice quality in various degrees during different periods, especially the combined stress within 21 days of grain filling stage.