Research On The Evaluation Method Of Wheat Tolerance To Sitobion Avenae (Hemiptera:Aphididae) Based On Photosynthetic Physiology

As one of the three major grain crops in China,wheat facing the threat of many kinds of pests and diseases during its growth.The grain aphid,Sitobion avenae,is the main pest that limiting the yield formation in wheat grain filling stage.Wheat tolerance has obvious ecological advantages for aphid control.However,the aphid tolerant wheat varieties are scarce at present in China,and tolerance of wheat to aphid is rarely used for ecological control of wheat aphids.The evaluation of wheat tolerance to aphid is simple and the lack of clarity of the aphid resistance mechanism is the main limiting factor.To explore the photosynthetic physiological and biochemical characteristics and the accumulation and transport of assimilates in wheat under the condition of aphids.To explore the photosynthetic physiological and biochemical characteristics of wheat and the accumulation and transport rule of assimilates when affected by aphids,it is of great theoretical and practical significance to develop diversified and accurate methods for assessing wheat tolerance to aphid and breeding aphid tolerant varieties.In this study,19 wheat germplasm with different aphid tolerance levels were selected as research materials.Under the condition of artificial assisted control of aphid in protected areas,the photosynthetic physiological and biochemical characteristics and assimilate transport law of wheat were studied at filling stage.By investigating 16 traits related to yield components,gas exchange,photosynthetic capacity,light energy use efficiency and water use efficiency and calculating their aphid tolerance response coefficients,inter-varietal inter quartile analysis of varietal variance was applied to determine the optimum level of damage for wheat tolerance identification.It also provides an in-depth exploration of the methods for assessing wheat tolerance to aphid and the mechanisms of tolerant wheat through comprehensive multivariate statistical analysis.The following main results were obtained:1.Aphid tolerance index method（1000-grain weight loss rate/aphid level）was used to evaluate the 19 wheat germplasm to aphid.The results showed that 5 germplasm were super tolerant（1000-grain weight increased after aphid damage）,1 germplasm was high tolerant,3 germplasm materials were low tolerant,2 were low susceptible,1 was medium susceptible and 7 were high susceptible.2.Under aphid damage,the decline in the weight of each nutritional organ,grain weight,grain number,above-ground biomass,seeds and harvest index of aphid-tolerant varieties was less than that of aphid-susceptible varieties,and the thousand grain weight of super-tolerant germplasm even increased slightly.This suggests that appropriate aphid damage can improve the above-ground distribution of aphid-tolerant wheat and facilitate the transfer of assimilates from other organs to the seed to ensure stable wheat yields under moderate aphid damage.3.The net photosynthetic rate,SPAD value,transpiration rate,stomatal conductance,intercellular CO₂concentration and water use efficiency of aphid tolerant germplasm were mostly higher than those of aphid susceptible germplasm.The values of the photosynthetic characteristics of the aphid-tolerant germplasm increased with light aphid damage and decreased less with higher levels of damage;the aphid-sensitive germplasm was consistently reduced with aphid damage and rarely increased in compensation.4.Under aphid damage,pre-flowering translocation and translocation rate of wheat increased,but post-flowering assimilation and post-flowering contribution decreased,indicating that aphid damage affected the photosynthetic function of leaves and accelerated plant senescence,resulting in reduced accumulation of post-flowering assimilates and lower translocation of assimilates to the seeds.The contribution of pre-flowering assimilates to seeds varied considerably between varieties,with less pre-flowering assimilates contributing to seeds and more post-flowering assimilates contributing to seeds for aphid-tolerant germplasm relative to aphid-susceptible germplasm.This may be due to the fact that aphid-tolerant germplasm has more pre-flowering assimilates for the growth of nutritional organs,thus facilitating the maintenance of a high level of photosynthesis during the sensitive period of aphid damage to the plants at the filling stage.5.The flag leaf and glume NADH-MDH enzyme activities of the aphid-tolerant germplasm were not significantly different from the control after aphid damage.No significant changes in flag leaf NADH-MDH enzyme activity were observed in aphid-susceptible germplasm after aphid damage,but glume NADH-MDH enzyme activity was mostly reduced.Compared with the control group,the activity of NADH-ME enzyme in flag leaves and glume of aphid tolerant germplasm was not significantly changed,while that of aphid sensitive germplasm was significantly decreased.The activities of Rubisco carboxylase,PPDK and PEPC between aphid tolerant and sensitive germplasm were less varied after being harmed by aphids,which may be less involved in resisting aphid stress.6.The SPS enzyme activities of aphid-tolerant and aphid-susceptible wheat germplasm were more variable after aphid damage,indicating that sucrose accumulation in wheat under aphid damage was related to SPS enzyme activity.There were no significant changes in flag leaf SSase activity in most of the germplasm after varying degrees of aphid damage,indicating that SSase activity did not play a significant role in sucrose synthesis under aphid damage.The SS enzyme activity did not vary significantly between aphid-tolerant and aphid-susceptible germplasm.This suggests that there are differences in the mechanisms regulating sucrose accumulation in flag leaves of different aphid tolerant wheat.The contribution of different wheat varieties to sucrose synthesis was not consistent,with aphid tolerant germplasm having a greater role for SPS enzyme activity and a smaller role for SS enzyme activity in sucrose synthesis compared to aphid susceptible germplasm.7.The results of the correlation analysis showed that in the absence of aphid,the wheat compositional tolerance to aphid was negatively correlated with yield traits such as chlorophyll SPAD,Rubisco carboxylase activity in the spike glumes and assimilate accumulation.Wheat tolerance at low aphid levels was negatively correlated with chlorophyll SPAD,pre-flowering dry matter transport and glume PPDK enzyme activity,but positively correlated with dry matter accumulation rate;Wheat tolerance at high aphid levels was negatively correlated with photosynthetic characteristics,post-flowering dry matter accumulation and transport,and most assimilate synthesis and accumulation indicators,in addition to positive correlations with grain number,thousand grain weight,pre-flowering dry matter accumulation and transport,and flag leaf Rubisco carboxylase activity.The relationship between low aphid damage and wheat tolerance is not clear.The strong correlation between wheat tolerance and photosynthetic assimilation-related indicators at high aphid levels.This suggests that wheat with high tolerance to aphid is more photosynthetic and has a higher capacity for assimilate accumulation.8.The quartile method was used to describe the degree of germplasm variation,and the quartiles of tolerance response coefficients in most traits were the largest among varieties when the aphid level was 3.Therefore,the moderate degree of damage could be used as the optimal damage for tolerance identification of wheat to aphid.9.The results of principal component analysis showed that the response coefficients of tolerance of 16 agronomic traits could be simplified to 5 principal components.They can reflect yield composition,gas exchange,photosynthetic capacity,light use efficiency and water use efficiency.Based on the contribution rate of principal component and membership function analysis,the five principal component values could be further simplified into a comprehensive evaluation index D of wheat tolerance to aphid.D value can be used to evaluate tolerance of wheat germplasm.10.The correlation equation between wheat tolerance index（TI）and response coefficients of tolerance in 16 characters was established by stepwise regression analysis:TI=-0.672HI+0.498GP-0.442VW（R²=0.97,F=133.05,P<0.001）.According to this equation,the response coefficients of harvest index（HI）,grain number per spike（GP）and stalk weight（VW）were the key indexes affecting wheat tolerance to aphid.The tolerance level of wheat can be accurately predicted by using multiple stepwise regression analysis.In summary,compared to aphid-sensitive germplasm,aphid-tolerant germplasm is less affected by photosynthesis and suffers less yield loss when damaged by the aphid.Higher translocation of assimilates to the seeds after flowering and less reduction in photosynthetic enzyme activity are responsible for maintaining higher yields in aphid-tolerant germplasm.In addition,19 wheat varieties were identified for aphid tolerance using the aphid tolerance index method and the reliability of the method was verified by multivariate statistical analysis.