Study On Ecological Adaptability Difference And Mechanism Of Japonica Rice In The Middle Reaches Of The Yangtze River

In recent years,Hubei,Anhui and other provinces in the middle reaches of the Yangtze River have implemented the"Indica rice to Japonica rice"project.Most of introduced middle-season japonica rice varieties have showed unstable yield and poor quality,due to the differences in the ecological adaptability,which seriously restricts the development of japonica rice in the middle reaches of the Yangtze River.Therefore,it is very important to clarify the ecological adaptability difference and mechanism of japonica rice in the middle reaches of the Yangtze River in order to stabilize and guarantee a high-quality and high-yield production of japonica rice in the middle reaches of the Yangtze River and promote the development of japonica rice production.This study conducted sowing date test with 5 types of rice?inbred japonica rice,hybrid japonica rice,indica/japonica hybrid rice,hybrid indica rice and inbred indica rice?in six typical ecological sites including Xiangyang,Zaoyang,Suizhou,Jinmen,Gongan and Wuxue in Hubei Province from 2014 to 2018.Meanwhile,we also carried out regional comparative experiments with 7 high quality japonica varieties?Nanjing 9108,Jing 565,Fengjing 3227,Wuyun Jing 80,Wanken Jing 2 hao,Yongyou 4949 and Jingliangyou 4466?in Zaoyang,Hubei Province,Luan,Anhui Province,and Yangzhou,Jiangsu Province.We investigated the differences in growth process,yield,quality and source-sink relationship of japonica rice in different ecological zones and under different sowing dates,and clarified its main meteorological impact factors.We further analyzed the mechanism of the effect of source-sink relationship and high temperature during grain filling on the quality of japonica rice.The main findings are as follows:?1?The study on growth process of japonica rice in the middle reaches of the Yangtze River showed that the sowing-heading days were significantly shortened with delaying sowing date,and the heading-maturity days were prolonged.With delaying sowing date,the sowing-heading days were shortened by a maximum of 30 days,and the heading-maturity days were extended by a maximum of 15 days.Moreover,the difference in days between heading date to maturity date of japonica rice in different regions could be up to 27 days.The main factor for the obvious changes in the growth process was temperature.The correlation analysis results show that the sowing-heading days was significantly negatively correlated with the average temperature during the vegetative stage?VT?and the average temperature before flowering?FT?,while the heading-maturity days are significantly negatively correlated with the average temperature during the grain filling stage?GT?.?2?In the middle reaches of the Yangtze River,the average yield gap of japonica rice with different sowing dates of different areas was up to 2 t hm^-2-4 t hm^-2.The yield gap of different sowing dates was 1.1 t hm^-2-3.5 t hm^-2.Optimizing sowing date could increase japonica yield and narrow the yield gap.This study found that the yield of japonica rice was significantly negatively correlated with VT and GT?r=-0.285**and-0.269**,n=96?.This study also found that when 21.5?<VT<24.2?and21.7?<GT<25.6?,a higher yield of japonica rice could be obtained.?3?In the middle reaches of the Yangtze River,japonica rice qualities were significant differences in different sowing dates and different regions.The difference in head rice rate of japonica rice at different sowing dates ranged from 4.9%to 40.9%.The difference in chalky grain ratio ranged from 4.3%to 34.5%.The difference in chalkiness degree ranged from 1.3%to 34.8%.The analysis found that the main factor leading to changes in the quality of japonica rice was the temperature before heading stage.The correlation results showed that the head rice rate of japonica rice was significantly negatively correlated with the temperature during grain filling.At the same time,we observed that the peak viscosity,breakdown and setback were significantly positively correlated with GT.Our study futhers showed that high temperature would induce an 8.0%to 41.5%increase in chalky grain ratio of japonica rice,and a 1.2%-25.8%increase in chalkiness degree,which significantly increased the rice pasting temperature while decreased amylose content.Besides,our studies showed that the high temperature during the grain filling stage mainly affected the transport of dry matter and non-structural carbohydrates in the sheath of the plant to the grain and affected the starch branching enzyme activity in the grain,resulting in a slower grain filling rate,which ultimately leads to a reduction in grain weight,and in turn leads to the grain significant increase in chalkiness and changes in starch properties.?4?In the middle reaches of the Yangtze River,the source of japonica rice varieties significantly decreased,and the leaf area/sink potential and stem and sheath weight/sink potential significantly decreased with delaying the sowing date.Studies showed that the leaf area index of japonica rice was negatively correlated with VT,RT and FT.Further research on the mechanism of the source-sink relationship on the quality formation of japonica rice was conducted.The results showed when the leaf area index,the specific leaf weight,the leaf-sink ratio and the stem-sink ratio were relatively larger,japonica rice quality would improve significantly.The main performance was to reduce the protein content of japonica rice by 0.93%-1.07%,the chalkiness decreases by 4.7%-22.4%,the pasting temperature decreases significantly,the total starch content increases by 4.6%-6.2%,and the taste value increases significantly.At the same time,it was found that the specific leaf weight is extremely significantly positively related to rice yield.Studies showed that it was beneficial to increase the net assimilation rate and promote the dry matter transport of sheath,which makes the grain filling rate slower before the grain reaches the peak of filling,and the grain filling rate is faster after the peak of filling.Then,the final grain weight of the grain is increased,the synthesis of grain starch is promoted,the protein content of the grain is significantly reduced,and the appearance quality of rice,starch gelatinization characteristics and taste quality of rice are significantly improved.In summary,there were significant differences in growth process,yield,quality and source-sink relationship of japonica rice in different ecological zones and under different sowing dates in the middle reaches of the Yangtze River.The formation of the difference was mainly related to the average temperature before heading?especially VT?and GT.When 21.5?<VT<24.2?and 21.7?<GT<25.6?,a higher yield of japonica rice could be obtained.At the same time,according to the correlation between the source-sink relationship and VT and quality,and the correlation between GT and quality,we speculated that high quality and high yield can be obtained when VT and GT were relatively low.We speculated that higher yields and better rice quality could be obtained in this temperature range.According to this,comprehensive local meteorological data retrieval results for many years can be used as a reference basis for determining suitable varieties and suitable sowing dates in the middle reaches of the Yangtze River.