Alfalfa Wilt (Verticillium Alfalfae) In China

Alfalfa Verticillium wilt(AVW)caused by Verticillium alfalfae is a destructive disease.The pathogen is a quarantine organism in Entry-exit Inspection and Quarantine in China.The disease has been reported in China,but the distribution,occurrence and control techniques are not well studied in China.This thesis was carried out to investigate the distribution of the disease,as well as study the infection site,host range and biological characteristics of the pathogen.In addition,the resistant cultivars and resistance mechanism were also researched.The main results are as follows:1.Verticillium wilt of alfalfa occurred in Gansu Province,including Zhangye city,Jiuquan city,Wuwei city,and Jinchang city,but did not occurred other surveyed sites in other province,including Changji City in Xinjiang Autonomous Region,Suihua City in Heilongjiang Province,Cangzhou city in Hebei Province,Chifeng City in Inner Mongolia Province,Guyuan City in Ningxia Autonomous Region,and Kunming City in Yunnan Province.The disease has masked symptom,and the field masked symptom rate was 11.11%-30.55%.The whole leaf of the plant turns yellow,wilting and desiccation from bottom to upper were the main diagnosis symptoms of the disease,and the field identification accuracy based on V-shaped necrosis was 22.22%-83.33%.2.Verticillium wilt significantly affected the dry weight and nutrient contents of alfalfa with different varieties and plant ages,among which plant dry weight,crude protein,organic carbon,total nitrogen(N),total phosphorus(P),fructose and starch contents decreased by 36.96%,40.82%,47.50%,44.29%,29.68% and 32.86%,respectively.Crude fiber and sucrose contents increased by 21.55% and 35.99% on average,respectively.3.The optimal medium for colony growth of Verticillium alfalfae was Czapek,optimal carbon source were maltose and lactose,optimal nitrogen source were sodium nitrate,ammonium nitrate and ammonium chloride,optimal medium for sporulation was CMA,optimal humidity for conidia germination was 98 ± 1% RH at 20 to 25?.The lethal temperature for mycelia was 55?for 10 min.Conidia died at 55? for 15 min.4.The artificial inoculation experiment demonstrated V.alfalfae can infect seven non-alfalfa plant species,including erect milkvetch,sainfoin,common vetch,sunflower,potato,cotton,and bluish dogbane.In addition,seven kinds of inoculation methods showed that the pathogen could invade from roots,stems and leaves,and spread to all other tissues.Among them,the spore suspension soaking seed inoculation method is the most convenient and effective.5.The result of resistance evaluation test of 30 alfalfa cultivars showed that,the high resistant cultivars to AVWwere Gannong 4,Zhongmu 1,WL343 HQ and other8 cultivars,the resistant cultivars were Xinjiang Daye,Gannong 6,Zhongmu 3,Adrenalin and other 9 cultivars,the moderate resistant cultivars were Gannong 9,Aohan and other 4 cultivars.Percentage of alfalfa cultivarsin China were 18.18%,53.85% and 66.67% in HR group,R group and MR group,respectively.This indicates Chinese cultivars have low resistance to AVW.6.The highly resistant cultivar WL343 HQ and moderately resistant cultivar Dryland obtained from resistance evaluation test were used to compare the physiological and biochemical indexesat7,14,21 and 28 d after inoculated with Verticillium alfalfae.Results showed that the net photosynthetic rate,stomatal conductance,activities of SOD and POD,and concentrations of JA and SA in diseased WL343 HQ cultivar were higher,and the MDA concentration was lower than those of diseased Dryland cultivar.In addition,the WGCNA analysis showed that the cultivar WL343 HQ inoculated with V.alfalfae has more transcription factors related to plant growth and disease resistance inthe hub genes of network modules than cultivar Dryland,and most of the differentially expressed genes(DEGs)were classified into the pathways of photosynthesis,photosynthesis-antenna protein,linolenic acid metabolism,carbon fixation in photosynthesis,MAPK plant signaling,phenylpropanol biosynthesis,carbon metabolism,and glutathione metabolism.