Screening And Identification Of Heat-tolerant And Highly Regenerative Rice Varieties And Their Physiological Mechanisms

Ratoon rice is a new type of rice cultivation mode,which has the advantages of high economic efficiency,low labor demand and significant ecological benefits,etc.In recent years,the cultivation ratoon rice in China has been increasing year by year.However,the lack of ratoon rice varieties and the frequent occurrence of extreme high temperature weather caused by global warming have seriously affected the cultivation and promotion of ratoon rice in the middle and lower reaches of Yangtze River in China.At present,there are many studies on the screening and identification of ratoon rice varieties,but the screening and identification of rice varieties with both heat resistance and strong ratooning ability have not been reported,and the mechanism of heat resistance and strong ratooning ability of rice needs to be studied in depth.Therefore,in this study,we screened and identified rice varieties that were widely grown in the middle and lower reaches of Yangtze River,with the aim of screening out rice varieties with good yield,high quality,heat resistance and strong ratooning ability,and elucidating the mechanisms of heat resistance in the main crop season and strong ratooning ability in the ratoon crop season.The main results are as follows.1.We used a combination of field and pot planting to compare the yield,heat resistance at flowering(heat resistance index),rice quality and regenerative power of the field and pot planting treatments,and used the affiliation function to construct a method for identifying and selecting rice varieties with high yield,high quality,heat resistance and strong regenerative power.Based on the average affiliation function values,five varieties were selected as suitable for regeneration in the middle and lower reaches of Yangtze River,namely Yongyou15,Huiliangyou898,Longliangyou534,Yliangyou900 and Quanyousimiao.In addition,two varieties with similar fertility but different yield,quality,heat resistance and regeneration ability,Yongyou15(YY15)and Yliangyou1(YLY1),were selected to further study their mechanism of action.2.The mechanism of heat resistance during flowering was investigated using YY15(heat-resistant type)and YLY1(heat-sensitive type)as materials.The study showed that heat stress at anthesis significantly reduced spikelet fertility,stigma pollen germination and pollen tube elongation in the two rice varieties,with YLY1 being inhibited to a greater extent than YY15.Under heat stress,the increase of reactive oxygen species(ROS)in the pistil tissue of YLY1 was significantly higher than that of YY15,which was the main reason for the difference in heat tolerance.Transcriptome analysis showed that glutathione metabolism and flavonoid biosynthesis pathways were the main mediators of heat tolerance in both varieties at high temperatures,showing up-regulation or no change in YY15,and down-regulation in both YLY1.Further studies showed that the increase in GST activity,proanthocyanidin content and antioxidant enzyme activity in the pistil tissue of YY15 was significantly higher than that of YLY1.In addition,exogenous potassium fulvic acid(FA)significantly improved spikelet fertility of YY15 under high stress,while GST activity,proanthocyanidin content and antioxidant capacity were significantly increased.In view of this,we hypothesize that GST mainly regulates flavonoid accumulation and antioxidant capacity to maintain ROS homeostasis and improve heat tolerance in rice.3.YY15(strong regeneration type)and YLY1(weak regeneration type)were used as materials to study the mechanism of strong regeneration action in rice.Under both field and pot conditions,the yield and regenerative power of YY15 in the main and ratoon seasons were significantly higher than those of YLY1.Transcriptome analysis showed that the differential genes of the two varieties were mainly enriched in carbohydrate metabolism,phytohormone signaling and energy metabolism.Except for GAs,the carbohydrate,IAA,ZR,ABA,ATPase and ATP contents of YY15 node were significantly higher than those of YLY1.In addition,exogenous FA significantly increased the regenerative power of both varieties,and the phytohormone and ATPase contents of both varieties were increased to different degrees,but the carbohydrate and ATP contents were decreased.Therefore,we hypothesize that ATPase,hormone and sugar signals in stem nodes jointly regulate axillary bud germination in rice.