Evaluation Of The Resistance Of Different Alfalfa To Common Leaf Spot And The Effect Of Pseudopeziza Mdicaginis Infected Leaves On Carbon And Nitrogen Metabolism

Alfalfa common leaf spot caused by Pseudopeziza medicaginis occurs in alfalfa producing areas all over the world,which seriously affect the yield and quality of alfalfa.Breeding and application of disease-resistant varieties are the most effective strategies to prevent and control the disease.In this study,we evaluated the resistance of different alfalfa varieties to common leaf spot The relationship between physical structures of varieties with different resistance and water content of leaves at different leaf positions were analyzed.The effects of P.medicaginis infection on carbon and nitrogen metabolism of alfalfa leaves were studied.The paper aims to provide a theoretical basis for disease resistance breeding of alfalfa and analyzing the effect of pathogen infection on alfalfa quality.The primary conclusions are follows:(1)The resistance evaluation of 40 different alfalfa varieties showed that different alfalfa varieties have different resistance to common leaf spot.The disease index of reindeer was the lowest and the relative resistance index was the highest.So,the reindeer was medium resistance(MR)species.The relative resistance index of 14 varieties,such as WL354HQ,WL298HQ,Concep,SPYDEK and so on,ranged from 0.20 to 0.39,which showed medium susceptibility(MS).The relative resistance index of 14 varieties,such as WL712,WL363HQ,Adrenalin,MF4020 and so on,ranged from 0.10 to 0.19,which showed susceptibility(S).The relative resistance index of 11 varieties,such as Siriver,VNS,3015,northern SLT and so on,were all less than 0.10,which showed high susceptibility(HS).Meanwhile,cluster analysis showed that 40 tested varieties could be divided into four groups of medium resistance,medium susceptibility,susceptibility,and high susceptibility.The results of cluster analysis were basically consistent with those of relative resistance index.(2)Observation on physical structure characteristics of alfalfa epidermis of different varieties showed that there were some differences among varieties in stomatal density,stomatal aperture and guard cell size.However,the correlation with resistance to common leaf spot was not strong.From the aspect of trichomes,although there was a positive correlation between trichomes density and disease index,the correlation was not strong and did not reach a significant difference level.The correlation coefficient between trichomes length and disease index was extremely small,and it had nothing to do with disease resistance.(3)The relationship between leaf water content and resistance in different leaf positions showed that there was a certain correlation between leaf water content and disease index and relative resistance index.The water content of the leaves at the low position was the highest,which showed positive correlated with the disease index and negative correlated with the relative resistance index;Secondly,the water content of the leaves at the middle position;The leaves at the in high leaf position was the lowest.Furthermore,the correlation coefficients of water content of the leaves at the low position with disease index and relative resistance index were 0.3015 and-0.3002,respectively.The correlation between leaves water content in other positions and disease index and resistance index was not strong.(4)The effects of P.Mdicaginis infection on carbon and nitrogen metabolism of alfalfa were showed that the percentage of soluble sugar and reducing sugar in diseased leaves was significantly lower than that in healthy leaves.The percentage of sucrose and fructose were slightly higher than that in healthy leaves,but there was no significant difference between healthy leaves and in diseased leaves.The content of soluble protein and free amino acid decreased,but the decreasing trend was not significant The activities of nitrate reductase and glutamine synthetase increased significantly,while the activities of glutamate dehydrogenase decreased significantly,and the differences between them and healthy leaves reached significant levels.It was concluded that the infection of P.Mdicaginis,to a large extent could affect the carbon and nitrogen metabolism of alfalfa,and thus affected the protein synthesis and photosynthesis in plants.