The Etiology Of Stemphylium Leaf Spot On Vegetables And Its Resistance To Boscalid In China

Stemphylium solani is an important plant pathogen,with a wide range of hosts.In recent years,vegetables leaf spot caused by Stemphylium was widely outbreaked in China,resulting in serious economic losses,the pathogen is still lack of systematic study.This study mainly focus on the population differentiation analysis based on the phenotype characters,pathogenicity and genetic diversity.Meanwhile,we also established effective detection techniques for S.solani monitoring and forecasting,analyzed the resistance of S.solani to boscalid,provided foundamental theory about development of fungicide,controlling Stemphylium on vegetables.1.During September 2013 to April 2015,the investigation of Stemphylium leaf spot was done in six provinces including Shandong,Beijing,Guangdong,Guangxi,Liaoning and Hainan and so on.The results showed that the dominant population of Stemphylium leaf spot on tomato,cowpean and romaine lettuce is S.solani.2.Nine phenotypes was observed in S.solani population based on colony morphology,which showed no relevance to hosts and district sources.However,conidial morphology has significant differencesin S.solani which is related to different hosts and district sources.3.The pathogenicity differentiation significantly exited in S.solani with different origins in China.Two obvious pathotypes were determined based on the pathogenicity test on tomato,cowpea and romaine lettuce.Pathotypes was closely related to hosts and geographical origin.Specifically,PA pathotype contained four sub-pathotype,among which PA1 exhibited low virulence to three tested hosts.PB pathotype consisted of three sub-pathotype showing very high pathogenicity to three tested hosts.There is distinguishable pathogenicity in the S.solani strains isolated from the same host or same geographical origin.4.A good innoculation method was developed in the process of S.solani infecting tomatoes,identified the hyphae infecting as a major infection way.In detail,multiple buds generated on the surface of leaves,hyphae elongated at all directions,secondary infection hyphae formed near the stomata,then expansion of infection was occured from the stomata to other cells in the leaves.5.Genetic groups of S.solani was related to host to some degree,while irrelevant to geographic origins.One-hundred and five S.solani strains was divided into four genetic groups based on phylogenetic and molecular markers analysis.Abundant genetic variation for the S.solani from tomatoes,a certain degree similar to strains from other hosts,suggested that S.solani on other hosts may come from tomatoes,for cross-infections between different hosts and tomatoes,indicating some relationships between disease epidemics and cross-regional transportation of tomato seedlings.6.A detection technology of S.solani was established based on quantitative real-time PCR using Glyceraldehyde-2-phosphate dehydrogenase(gpd)gene as target.The sensitivity of this method was below 4.285×102 fg·?L-1,which was 1000-fold higher than common PCR.In our study,S.solani can be detected before observation of symptom,just 6 hours postinoculation on the plants.7.A LAMP detection methods for S.solani was established using gpd gene as target.The sensitivity of LAMP was 2.4×103fg·?L-1,which was 100-fold higher than normal PCR.Based on the color reaction of calcein,S.solani can be detected in the latent infection period with no symptoms.8.Sensitivity baseline of S.solani to boscalid was estabilished.Currtently,the resistance of S.solani to boscalid was occurred in China,including Histidine to Tyrosine in SdhB(SdhB-H272Y)and Histidine to Arginine in SdhC(ShdC-H134R)obtained from two mutations in succinate dehydrogenase subunits B and C.