Effect of various combinations of temperature during different phenological periods on indica rice yield and quality in the Yangtze River Basin in China

TU De-bao ,JlANG Yang ,ZHANG Li-juan ,CAl Ming-li ,Ll Cheng-fang ,CAO Cou-gui

1 National Key Laboratory of Crop Genetic Improvement,MOA Key Laboratory of Crop Physiology,Ecology and Cultivation (The Middle Reaches of Yangtze River),Huazhong Agricultural University,Wuhan 430070,P.R.China

2 Rice Research Institute,Anhui Academy of Agricultural Sciences,Hefei 230031,P.R.China

Abstract Rice grain yield and quality declines are due to unsuitable temperatures from wide regions and various sowing dates.This study aimed to evaluate the effects of temperature on rice yield and quality at different phenological periods and obtain suitable temperatures for phenological periods in the Yangtze River Basin,China.This study conducted experiments on different sowing dates under different areas in the Yangtze River Basin to observe and compare the differences in rice growth,yield,and quality,controlling for regional varieties.The results showed significant differences in rice growth,yield,and quality among sowing dates and areas,which were related to the average daily temperature during the vegetative period (VT) and the first 20 days of the grain-filling period (GT20).In addition,there was a smaller variation in the average daily temperature in the reproductive period (RT) than in the two phenological periods.Therefore,according to the VT and GT20 thresholds of different yields and qualities,the experimental results were divided into four scenarios (I,II,III,and IV) in this study.In Scenario I,high head rice production (rice grain yield multiplied by head rice rate) and rice quality could be obtained.The head rice production of Scenarios III and IV was lower than that of Scenario I,by 30.1 and 27.6%,respectively.In Scenario II,the head rice production increased insignificantly while the chalky grain rate and chalkiness were 50.6 and 56.3% higher than those of Scenario I.In conclusion,the Scenario I combination with VT ranges of 22.8-23.9°C and GT20 ranges of 24.2-27.0°C or the combination with VT ranges of 23.9-25.3°C and GT20 ranges of 24.2-24.9°C,which can be obtained by adjusting sowing date and selecting rice varieties with suitable growth periods,is recommended to achieve high levels of rice grain yield and quality in the Yangtze River Basin.

Keywords: temperature,phenological period,grain yield,quality

1.lntroduction

As an important food crop,rice is the staple food for more than 50% of the global population (Macleanet al.2013).Studies have shown that rice production needs to increase by 70% by 2050 to meet market demand in the world(Koninget al.2008;Godfrayet al.2010).Besides,people have higher and higher requirements for rice quality with increasing living standards (Linet al.2020).As the largest rice producer and consumer,China produces 28%of the global rice yield (FAO 2020),among which 60%comes from the Yangtze River Basin (NBSC 2012).Most farmers in the Yangtze River Basin cultivate rice,which is their important source of income.The head rice rate and chalkiness play an essential role in determining the commercial value of rice (Lymanet al.2013).Therefore,promoting the rice grain yield and quality is of great significance to increasing farmers’ income,maintaining social stability,and achieving regional and global food security.However,rice grain yield and quality varied inexplicably with different cultivated areas and sowing dates (Palet al.2017;Liet al.2018;Baiet al.2019).

Variations in growth temperature may cause yield and quality differences in rice (Krishnanet al.2011;Zhouet al.2021).Previous studies investigating the influence of temperature on grain development have indicated that the high temperature during the grain-filling period increased the grain-filling rate and spikelet sterility and decreased grain weight,seed-setting rate,and harvest index,which finally decreased rice grain yield (Ahmedet al.2015;Bahugunaet al.2017;Xionget al.2017;Aliet al.2018).In addition,lower temperature also caused the degeneration of spikelets and increased spikelet sterility and influenced grain filling,resulting in low seed set and,finally,low rice grain yield (Wanget al.2013;Jiaet al.2019).High temperature during the grain-filling period is also harmful to grain quality,such as increasing chalky grain rate and chalkiness level and decreasing brown rice rate and head rice rate (Chenet al.2016;Abayawickramaet al.2017).Low temperature resulted in poor grain quality by changing amylose content and the crystalline structure of starch (Huet al.2020).However,these studies were usually performed using controlled temperature chambers.This approach is limited because it does not necessarily reproduce field conditions (Huanget al.2013).

In addition,like most crops,the whole rice growth season can be divided into three phenological periods:the vegetative,reproductive,and grain filling (Yoshida 1981).Studies have shown that each phenological period has its own growth characteristics and requires a suitable temperature.For example,in the vegetative period,high temperature reduces matter accumulation and shortens growth duration (Oh-eet al.2007;Ishiiet al.2011).Shimonoet al.(2007) reported that the temperature before the panicle initiation period is lower than 20°C,which increases the spikelet sterility.Besides,rice growth and development are also affected by high temperature during the reproductive period,which reduces pollen viability and spikelet fertility and inhibits starch deposition (Shahidet al.2018;Linet al.2020).These all indicate that temperature is important to various stages of rice growth,thereby impacting rice yield and quality (Krishnanet al.2011).

However,in actual production,it is almost impossible to keep rice at an appropriate temperature during every phenological period.Therefore,it is crucial to determine the comprehensive effect of temperature on rice yield and quality during different phenological periods,particularly under field conditions.This study conducted a two-year field experiment in four areas.The main objectives were to clarify: 1) the relationship between temperature at phenological periods and related agronomic traits,yield,and quality;2) the suitable temperature range for high rice grain yield and quality.

2.Materials and methods

A two-year field experiment was carried out in four major rice-producing areas in the Yangtze River Basin,China with a humid subtropical climate,including Suizhou City(31.64°N,113.23°E),Jingmen City (30.71°N,112.37°E),Gong’an City (30.05°N,112.29°E),and Wuxue City(30.01°N,115.75°E).

2.1.Materials and study design

The soil properties in the four study areas were determined from the upper 20 cm layer: pH 5.79-6.01,17.2-20.3 g kg-1organic matter,0.8-1.5 g kg-1total N,5.45-8.91 mg kg-1available Olsen-P,and 47.6-115.72 mg kg-1exchangeable K.The treatments were arranged in a split-plot design with sowing dates as main plots and cultivars as subplots.Six different sowing dates,April 15,April 25,May 5,May 15,May 25,and June 4 were set as main plots treatments.The regional cultivars with different temperature sensitivities were designated as the subplots,including Huanghuazhan (HHZ),an inbredindicarice,and Yangliangyou 6 (YL6H),a two-line hybridindicarice.They were grown under irrigation single rice system.

The seedlings were transplanted (28±3) days after sowing at a hill spacing of 13 cm×30 cm,with three and two seedlings per hill for HHZ and YL6H,respectively.The high-yield and high-quality fertilization levels (HHZ:195 kg ha-1total N,97.5 kg ha-1P2O5,195 kg ha-1K2O;YL6H: 225 kg ha-1total N,112.5 kg ha-1P2O5,225 kg ha-1K2O in all test areas) were chosen in this study (Tuet al.2020).Fertilizer-N was applied in four splits: 40%as basal,20% at tillering,20% at panicle initiation,and 20% two weeks after panicle initiation.Fertilizer-P was fully applied as basal,and fertilizer-K was applied in two splits of 50% as basal and 50% at panicle initiation.The fertilizers were used in the forms of compound fertilizer,urea,calcium superphosphate,and potassium chloride.The field was flooded after transplanting,and a floodwater depth of 3-5 cm was maintained until a week before maturity,except that the water was drained at the maximum tillering stage to reduce unproductive tillers.Field management practices were conducted according to the standards recommended for the region.To avoid biomass and grain yield losses,chemicals were applied to intensively control insects,diseases,and weeds.

2.2.Meteorological data collection

The meteorological data were obtained from small weather stations (AWS 800,Campbell Scientific,Inc.,Logan,UT,USA) near the experimental fields.

2.3.Yield and yield components

At maturity,plants from an area of 5 m2in the center of the plot were harvested,and subsequently,the rice grain yield was adjusted to 13.5% moisture content.Twelve plant samples from each plot were collected randomly (with the three outermost rows removed to minimize the border effect) to calculate yield components.Panicles were hand-threshed.Filled and unfilled grains were separated by submerging them in tap water;a seed blower was used to separate half-filled and empty grains.Subsamples were taken to manually count the total number of filled,half-filled,and empty grains to assess grains per panicle and seed-setting rate.In addition,grain weight was estimated from filled grains.

2.4.Rice quality

Mature rice was threshed after harvest,air-dried,and stored at room temperature for three months until testing.A rubber roller sheller (BLH-3250,China) was used to shell,and the brown rice rate was measured.The brown rice was milled with a rice polishing machine (Pearlest,Kett,Japan),and the head rice rate was measured.In addition,the appearance quality of rice was measured and analyzed with a scanner (Epson Expression 1680 Professional,Epson,the USA) and Image Analysis Software.

2.5.Data analysis

The whole rice growth season included the vegetative period (from rice sowing to panicle initiation),reproductive period (from rice panicle initiation to heading),and grainfilling period (from heading to physiological maturity).The days from sowing date (SD) to heading date (HD) and from HD to maturity (MD) were calculated in this study.The average daily temperatures during the vegetative period (VT),the reproductive period (RT),and the whole growth season (WT) were calculated separately.In the grain-filling period,studies showed that the temperature during the first 20 days of the grain-filling period played a key role in rice yield and quality (Oh-eet al.2007;Gonget al.2013;Tuet al.2020).Based on this,the average daily temperature during the first 20 days of the grain-filling period (GT20) was calculated in this study.Furthermore,the experimental data set was divided into different scenarios according to temperature thresholds for different rice yields and qualities.

The differences in properties among cultivars were minimized by applying the average and standardized management to evaluate the responses of rice growth to temperature changes (Denget al.2015;Tuet al.2020).The standardized data were defined as ‘relative data’ and calculated as follows:

Relative rice grain yield (RGY)=The yield of a variety on one sowing date in one area in one year/Average yield of this cultivar on six sowing dates in two years in all areas.Based on this,relative parameters of agronomic traits such as relative brown rice rate (RBR),relative head rice rate (RHR),relative chalky grain rate (RCR),and relative chalkiness level (RCL) were also determined.

Analysis of variance (ANOVA) was used to analyze the difference in rice quality.The correlation analysis was conducted to determine the relationship between the variations of temperature in different phenological periods and relevant agronomic traits.Data analysis was performed by SPSS 21 and Microsoft Excel 2010.The graphs were prepared by using SigmaPlot 10.0.In addition,the conditional inference tree analysis was performed using the ‘partykit’ package in R (R Development Core team 2016).

3.Results

3.1.Temperature at different phenological periods

WT showed a small change (less than 1.1°C),while the difference in daily average temperature in each phenological period was large (Table 1).The VT varied greatly,and the largest variation range among sowing dates in each area reached 3.0-4.4°C.Similarly,the GT20 also varied greatly,and the maximum range of change among sowing dates in each area reached 2.5-4.7°C.However,the variation of RT was smaller than that of the two phenological periods,and the maximum range of change among sowing dates in each area was below 2°C.There were also significant differences in temperature among different areas.The temperature in Gong’an and Wuxue was higher than that in Suizhou and Jingmen.

3.2.Differences in rice yield and quality in experimental areas and sowing dates

Among different locations,the rice grain yield in Suizhou was significantly higher than that of other locations(Fig.1).In addition,there were larger gaps in rice grain yield among different sowing dates,and the maximum gap was over than 5 t ha-1.There were also significant differences in rice quality among different sowing dates.The maximum differences in brown rice rate,head rice rate,chalkiness level and chalky grain rate among different sowing dates were 13.5,33.9,54.9,and 17.9%,respectively (Table 2).In addition,there were significant differences in rice quality among areas.

Table 2 Range of rice quality among areas and cultivars across sowing dates1)

Fig.1 The box-plot graph of rice yields under different sowing dates and areas.A,the rice grain yield of Yangliangyou 6 (YL6H);B,the rice grain yield of huanghuazhan (HHZ).Different letters indicate significant differences at the 0.05 level.

Table 1 Range of mean daily temperature (°C) of two cultivars (±SE) in different phenological periods across six sowing dates in different areas in Hubei Province1)

3.3.Correlation among relative agronomic traits,rice yield,rice quality and temperature in different phenological periods

Results showed that VT had a significantly negativecorrelation with RGY,and the absolute value of the correlation coefficient was 0.30＊＊(P＜0.01,n=96) (Fig.2).In addition,VT was significantly negatively correlated with relative grains per panicle (RGP) and relative SD-HD(RSD-HD),but it was positively correlated with relative panicle number (RP).GT20 had a significant negative correlation with the relative HD-MD (RHD-MD) and a significant positive correlation with the seed-setting rate and 1 000-kernel weight.However,all relative agronomic traits had no significant correlation with RT.From the correlation analysis of yield and yield component factors,it was found that the correlation between RGY and RGP (r=0.64＊＊＊;P＜0.001) was greater than that between RGY and RP(r=0.30＊＊;P＜0.01),and between RGY and relative seedsetting rate (RSR) (r=0.19＊;P＜0.05).In addition,RHD-MD had a significantly positive correlation with RGY (r=0.51＊＊＊).

In terms of quality,rice’s processing quality and appearance quality were also significantly related to the temperature at phenological periods.The RBR and RHR had extremely significant and negative correlations with GT20,with coefficients of -0.402＊＊and -0.344＊＊,respectively (Table 3).As for the appearance quality of rice,the RCR and RCL were extremely negatively correlated with VT (r=-0.294＊＊andr=-0.281＊＊),and they were also extremely significantly negatively correlated with RT (r=-0.417＊＊andr=-0.348＊＊).

3.4.Optimal temperature range for high yield and quality

The conditional inference tree analyses of temperature,rice growth,and yield are shown in Fig.3-A (R2=0.58,RMSE=0.12).Results showed that the HD-MD was an important factor affecting rice grain yield.In addition,VT also had a greater impact on it.In the field environment,when the RHD-MD was greater than 0.9 and the VT was less than 23.9°C,the RGY reached 1.18.When the RHDMD was greater than 1.04 and VT was between 23.9 and 25.0°C (23.9°C＜VT＜25.0°C),the RGY reached 1.11.From the relationship between RHD-MD and temperature,it could be seen that when GT20 was less than 27.0°C and VT was less than 25.3°C,the RHD-MD was greater than 0.9;when GT20 was less than 24.9°C and VT was less than 25.3°C,it was greater than 1.04 (Fig.3-B and C).

As for the appearance quality of rice,when VT was greater than 22.3°C and GT20 was between 24.2 and 27.5°C (24.2°C＜GT20＜27.5°C),the RCR was less than 1,and the RCL was also less than 1 (Fig.3-D and E).In terms of rice processing quality,when GT20 was less than 26.2°C,the RBR was greater than 1.When GT20 was less than 26.2°C and VT was between 22.8 and 25.3°C (22.8°C＜VT＜25.3°C),the RHR was greater than 1(Fig.3-F and G).

Fig.3 Trends of growth duration,grain yield and quality under different combinations of average daily temperature during the vegetative period (VT) and the first 20 days of the grain-filling period,respectively (GT20).A,conditional inference tree of different variables’influence on rice yield.B and C,distribution of relative relative days from heading date (HD) to physiological maturity (MD).D,relative chalky grain rate (RCR).E,relative chalkiness level (RCL).F,relative brown rice rate (RBR).G,relative head rice rate (RHR).H0.9,the relative value was higher than 0.9;L0.9,the relative value was lower than 0.9;H1.04,the relative values were higher than 1.04;L1.04,the relative values were lower than 1.04;H1,the relative value was higher than 1;L1,the relative value was lower than 1.

Fig.3 (Continued from preceding page)

According to the combination of VT and GT20 thresholds for different rice yields and qualities,the experimental data set was divided into four scenarios(Table 4).In Scenario I,the high head rice production(rice grain yield multiplied by head rice rate) and good appearance quality were obtained.Compared with Scenario I,the relative head rice production (RHRP)was reduced by 30.1% (III) and 27.6% (IV),respectively,and the increase in grain yield was not significant (II).However,the RCR and RCL of Scenario II were 50.6 and 56.3% higher than those of Scenario I,respectively.

Table 3 Relationships between rice quality and temperature during different phenological periods1)

Table 4 Mean relative head rice production (rice grain yield multiplied by head rice rate) and quality classification in different temperature thresholds1)

4.Discussion

There were significant differences in rice grain yield and quality under different areas and sowing dates.Many studies have shown that temperature has the greatest impact on rice growth,yield,and quality among climate factors (Cheng and Zhong 2001;Krishnanet al.2011;Chenet al.2013).In our study,although there was a small difference in the average daily temperature during the growing season among different sowing dates (the difference was less than 1.1°C),the rice growth was not the same.This indicated that the temperature and its combination at phenological periods played an important role in determining rice growth,yield,and quality.Results showed that the difference between VT and GT20 on different sowing dates was significantly greater than that between WT and RT.Denget al.(2015) also found that the average daily temperature during the vegetative period and the grain-filling period with different sowing dates had a large variation.In addition,our results indicated that SD-HD was extremely negatively correlated with VT,and HD-MD was extremely negatively correlated with GT20.Similarly,Ishiiet al.(2011) reported that high VT accelerated rice growth,leading to 4-7 days earlier heading and flowering,and high temperature during the filling period accelerated leaf senescence and shortened the duration of grain filling (Oh-eet al.2007;Kimet al.2011).Therefore,we proposed that shifting the sowing date to match the optimal VT and GT20 is a strategy to improve rice growth.

The conditional inference tree analyses were conducted to identify factors that had the strongest impact on crop yield (Lollatoet al.2018;Mourtziniset al.2019).In our study,the conditional inference tree analyses showed that HD-MD played the most important role in determining rice grain yield.This result may be attributed to the fact that the final grain weight is the product of the rate and duration of grain filling (Krishnanet al.2011).In addition,there was an extremely negative correlation between HD-MD and GT20.Meanwhile,our results showed that the RGY was lower than 1 when the RHDMD was lower than 0.9,induced by high GT20.It was similar that high temperature during the grain-filling period shortened grain-filling duration and decreased rice yield(Oh-eet al.2007;Kimet al.2011;Krishnanet al.2011).However,even though the RHD-MD was higher than 1.04,the RGY was still lower than 1 when the VT was higher than 25.0°C.This result may be attributed to the fact that high VT induced low grains per panicle,low pollen viability,and low spikelet fertility (Cheabuet al.2018;Shahidet al.2018).In our study,VT also had a strongly negative correlation with grains per panicle and seed-setting rate (Fig.2).Hence,we suggested that the combination of VT and GT20 plays an important role in determining rice grain yield in field practice.

In terms of rice quality,results displayed that there was a weak positive correlation between chalkiness and GT20 but a strong negative relationship between the chalkiness and VT.Contrary to the result,high GT significantly induced high chalky grain rate and chalkiness level (Linet al.2016;Abayawickramaet al.2017;Xionget al.2017),and high VT resulted in high chalky grain rate and high chalkiness level(Cheabuet al.2018).The inconsistency may be because previous research was mainly carried out in the greenhouse,where the temperature changed during one phenological period,and other phenological periods were in the same temperature condition.However,there was a strong negative correlation between VT and GT20 in our study(Fig.2),which suggested that a high GT20 always combined with low VT,and high VT always combined with low GT20.Although the high VT affected rice appearance quality by influencing rice pre-flowering development (Ishiiet al.2011;Cheabuet al.2018),the low GT20 was beneficial to rice grain filling and quality formation (Abayawickramaet al.2017).Therefore,we suggested that the combination of VT and GT20 also plays a key role in determining rice quality(especially rice chalkiness) in field practice.

High yield and quality are both important goals of rice production to meet market demands (Godfrayet al.2010;Linet al.2020).In this study,results showed that high yield and quality could be obtained in certain combinations of VT and GT20 thresholds.However,there were some differences between the combination of VT and GT20 thresholds for high yield and that for high quality.This indicated that optimizing the combination of VT and GT20 is a useful strategy to balance rice yield and quality.According to their different combination thresholds,the rice yield and quality could be divided into four scenarios.We found that both goals (high yield and high quality) were attained in Scenario I.Therefore,the combination of VT and GT20 can be optimized according to Scenario I (22.8°C＜VT＜23.9°C combined with 24.2°C＜GT20＜27.0°C or 23.9°C＜VT＜25.3°C combined with 24.2°C＜GT20＜24.9°C),which can be used as the basis of high-yield and high-quality rice production in the Yangtze River Basin.This finding will help ecological regions to select suitable rice varieties,determine suitable sowing dates,and improve rice grain yield and quality.

5.Conclusion

It is vital to select proper sowing dates and suitable varieties to match the crop phenology with the optimal local climatic conditions.This study showed extraordinary differences in rice yield and quality under different sowing dates and regions,which are mainly related to the daily average temperature at different phenological periods,especially VT and GT20.In Scenario I (the thresholds for VT are 22.8°C＜VT＜23.9°C and 24.2°C＜GT20＜27.0°C;the thresholds for GT20 are 23.9°C＜VT＜25.3°C combined with 24.2°C＜GT20＜24.9°C),high grain yield and quality can be obtained.This finding can be used as a reference for select rice varieties with suitable growth periods and determine suitable sowing dates to improve rice grain yield and quality in the Yangtze River Basin.

Acknowledgements

This work was supported by the Science and Technology Plan Project of Hubei Province,China (2012BLB228),the National Key Research and Development Program of China (2017YFD0301402),the National Natural Science Foundation of China (31701359),the Fundamental Research Funds for the Central Universities,China(2662017JC007) and the China Postdoctoral Science Foundation (2017M612477).

Declaration of competing interest

The authors declare that they have no conflict of interest.