Identification Of The Pathogen Of Alfalfa Powdery Mildew And Its Effect On The Quality Of Alfalfa

Alfalfa powdery mildew is a kind of common fungal disease,which is distributed in alfalfa producing areas all over the world.There is a lack of basic research on alfalfa powdery mildew in China,especially on the classification status of pathogenic bacteria,basic biological characteristics and the effect of disease on quality.In order to find out these problems,this study took potted alfalfa as the research object,combined with field investigation and laboratory test,carried out a systematic study on the pathogenic bacteria types,occurrence rules,biological characteristics of pathogenic bacteria,the ultrastructures of pathogenic bacteria invading the leaves of alfalfa and their physiological and quality effects,and obtained the following main research results:1.According to the characteristics of mycelium surface,conidia oval or ovoid,few of them have irregular branches,the pathogen of alfalfa powdery mildew in Ningxia was identified as Erysiphe poligoni DC..2.The results of biological characteristics showed that the optimum temperature range of conidia germination was 22℃-26℃,the optimum pH was 6.5,light promoted conidia germination,glucose,d-xylose and mannitol promoted conidia germination and germ tube growth,cysteine promoted germination,glycine promoted germ tube growth.3.Powdery mildew is mainly harmful to the front of alfalfa leaves and the surface of mycelium,which causes the leaves to fall off when it is serious.The temperature condition of powdery mildew is 20℃-24℃,the humidity condition is 40%-60%,and the forming condition of closed shell is 20℃-25℃,the humidity is about 70%,which takes about 42 days to form.4.Erysiphe poligoni DC.enters the epidermis cells through the haustorium to obtain nutrients,and the organelles in the hypha and haustorium are developed;the palisade tissue cells of the infected host are transformed from long strips to oblong ones,the stomatal channels are deformed,and the chloroplasts embedded in the inner wall of the cells are swollen and separated from the wall.5.With the increase of the severity of Alfalfa Powdery mildew,the SPAD value decreased significantly(P<0.05);the initial fluorescence(F0),the maximum fluorescence(Fm)and the maximum photosynthetic efficiency(Fv/Fm)of chlorophyll fluorescence parameters decreased,and the correlation between health and severity reached a significant level(P<0.05);the active parameters of the reaction center,the energy distribution ratio of PS Ⅱ and the light utilization efficiency of PS Ⅱwere all decreased Different degrees of influence.6.The CP,RFV,EE,P,Mg,K,ADF,rumen protein RUP,lignin and NDF of Alfalfa infected by powdery mildew decreased significantly(P<0.01).