Effects Of Drought Stress On Dry Matter Distribution And Yield Formation In Hybrid And Inbred Rice

Rice is a major food crop in China,and both hybrid and inbred rice are currently widely used in production.Drought and water shortage is one of the major factors limiting high rice yield,and studies on the difference in yield stabilization ability between hybrid and inbred rice under drought stress are still relatively limited.To further clarify the differences in response to drought stress between hybrid and inbred rice,this experiment used Meta-analysis and pot experiments to compare hybrid and inbred rice in terms of morphological and physiological characteristics,dry matter accumulation,and drought stress by setting conventional flooding（CK）and drought treatment（DS,soil water potential-30 k Pa±5 k Pa）.The differences in response to drought stress between hybrid rice and inbred rice in terms of morphological characteristics,dry matter accumulation and distribution patterns(mainly through ¹³C isotope markers to quantify photosynthetic carbon accumulation in rice and its distribution ratio in each organ),yield and water use efficiency were compared.The preliminary experimental results obtained are as follows:（1）Meta-analysis results based on data from relevant experiments over the past 30years showed that the period of drought stress,the degree of drought stress,and the rice varieties all affected the yield and yield components of rice.Rice suffered drought stress during the nutritional growth period was the most likely to reduce yield,but rice suffered drought stress during the nutritional growth period helped to increase filled grains of rice;Rice suffered drought stress during the reproductive growth period helped to increase the number of grains per spike of rice.Under severe drought stress,the yield of rice decreased the most,up to 27.8%,and mild drought stress could improve the filled grains of rice,the number of grains per spike and filled grains of rice decreased with the deepening of drought stress.The decrease in effective spike number under drought was less than that of inbred rice,and the decrease in filled grains of rice was greater than that of inbred rice;further subdividing hybrid rice and inbred rice into indica hybrid rice and indica inbred rice showed that the decrease in yield,effective spike number and filled grains of rice of indica hybrid rice under drought stress was greater than that of indica inbred rice;the number of grains per spike of indica hybrid rice decreased due to drought,and the opposite was true for indica inbred rice.（2）The results of the pot experiment showed that the plant height,individual leaf area,chlorophyll-related content,total root surface area,total root volume,average root diameter,root absorption area and active absorption area of hybrid rice were all greater than those of inbred rice varieties under conventional flooding irrigation,while the total reproductive period was shorter than that of inbred rice.Drought stress prolonged the whole-fertility period of rice,in which the nutritional growth period was prolonged and the reproductive growth period was shortened.Drought significantly reduced the plant height,leaf area per plant,average daily transpiration per plant,total root length,total root surface area,total root volume,root wounding flow rate,root absorption area and active absorption area of rice.Compared with inbred rice,the plant height,single plant average daily transpiration,total root length,total root surface area,and total root volume decreased more and the single plant leaf area decreased less after the hybrid rice experienced drought stress.Under drought stress,the root volume of hybrid rice decreased from 31.43 cm³ to 11.23 cm³ at the tillering stage,while that of inbred rice decreased from 13.71 cm³ to 8.63 cm³.Under drought stress,the leaf area and total root volume of hybrid rice were larger,while the total root length,total root surface area and average daily transpiration of inbred rice were larger.This indicates that under drought stress,hybrid rice has larger photosynthetic leaf area,while inbred rice produces more fine roots for water and nutrient uptake.（3）Application of ¹³C isotope labeling for quantitative analysis of photosynthetic carbon accumulation and allocation in rice under drought.Under conventional flooding,the dry weight of leaves and roots,soluble sugar and sucrose contents of leaves and stem sheaths at the spike and flowering stage,non-structural carbohydrate（NSC）contents of leaves,stem sheaths and roots,total photosynthetic carbon accumulation and photosynthetic carbon accumulation of spikes and roots were all greater in hybrid rice than in inbred rice varieties.Drought significantly reduced the dry weight of rice plants,with the greatest decrease in spike dry weight in rice,77.95%and 88.14%in hybrid and inbred rice,respectively,and the decrease in leaf and root dry weight in hybrid rice was greater than that in inbred rice.Under drought stress,the dry weight of all organs of hybrid rice was greater than that of inbred rice varieties in the early stage of fertility,and the biomass of its stems and spikes was greater than that of inbred rice in the late stage of fertility,while the biomass of leaves and roots was not significantly different from that of inbred rice;compared with inbred rice,the photosynthetic carbon accumulation and decrease rate of single plant of hybrid rice were greater,and the photosynthetic carbon accumulation of leaves,spikes and roots was greater,and the proportion of photosynthetic carbon allocated to the root system was smaller;in inbred rice,the soluble sugars of leaves,spikes and roots in the spike and flowering stage The soluble sugar content,sucrose content and NSC content of inbred rice were greater than those of hybrid rice at the spike and flowering stage,while the soluble sugar and NSC content of hybrid rice stems were greater than those of inbred rice.This indicates that the photosynthetic carbon accumulation in the leaves,spikes and roots of hybrid rice in the late reproductive stage was mainly used to maintain its biomass under drought compared to inbred rice.（4）Under conventional flood irrigation,the single plant yield of hybrid rice was significantly greater than that of inbred rice varieties,in which the fruit set rate of hybrid rice was significantly greater than that of inbred rice.Under drought conditions,the yield per plant and the number of grains per ear of rice decreased significantly,and compared with inbred rice,the yield per plant,fruit set rate and thousand grain weight of hybrid rice decreased more,and the number of spikes decreased less.The water use efficiency of hybrid rice was significantly higher than that of inbred rice under conventional flood irrigation,and drought had no significant effect on the water use efficiency of inbred rice,while the average water use efficiency of hybrid rice with a 25.51%decrease at a significant level,but compared to inbred rice,the water use efficiency of hybrid rice under drought However,compared with inbred rice,the water use efficiency of hybrid rice under drought was greater,mainly due to the accumulation of biomass in its aboveground parts.In conclusion,compared with inbred rice,hybrid rice still had greater photosynthetic carbon content for maintaining leaf,root,and spike growth under drought conditions,although the variability of each index was greater,and thus could obtain higher yield and biomass under drought.In contrast,inbred rice can maintain relatively stable yield and water use efficiency by increasing the proportion of photosynthetic carbon allocated in the root system to produce a large number of fine roots to maintain water and fertilizer uptake,resulting in a smaller decrease in root morphophysiological indexes after experiencing drought.