Identification Of Pathogen Causing Gummy Stem Blight Of Melon And Trichosanthes Kirilowii In Anhui Province And Screening Of Effective Fungicides

Gummy stem blight is a typical fungal soil-borne disease,which can damage many cucurbitaceae crops,such as cucumber,melon,watermelon and so on.The disease can occur in the whole growth period of cucurbit plants,endangering leaves,stems,vines,tendrils,pedicles,fruits,seeds and other parts of plants except roots.After infected,the yield and quality of melon crops are often seriously affected.The areas with serious diseases are often affected for several years,which seriously endangers the healthy development of melon industry in China.Especially in recent years,with the rapid development of facility melon cultivation techniques,the planting area of melon crops in Anhui Province has been expanding.Long-term multi-crop cultivation and successive years of cultivation have increased the base of the pathogenic fungi in the soil,leading to the occurrence and epidemic situation of gummy stem blight in an aggravated situation.In this study,the pathogenic fungi of melon and T.kirilowii were isolated and the species was identified by morphological analysis and multisite sequence analysis,and the sporulation induction methods of pathogens were screened.The biological characteristics of Melon and T.kirilowii were studied,and the inhibitory effects of seven commonly used fungicides on pathogens were determined by indoor mycelial growth rate method.The main results are as follows:1.Isolation and identification of the pathogen of melon and T.kirilowii gummy stem blight.Melon and T.kirilowii with typical symptoms of gummy stem blight were collected from the surrounding areas of Chaohu and Shucheng in Anhui Province.The isolated strains were isolated by tissue isolation from the diseased tissues and showed white colonies with well-developed,cottony,dense and slightly elevated aerial mycelium in the middle,white at the beginning and grayish after aging,dark green at the back of the colony,and dark brown at the end.The results of multisite sequence analysis of three locuss（ITS,TUB2 and LSU）showed that the pathogen of melon and T.kirilowii was Stagonosporopsis citrulli.2.Sporulation induction of melon and T.kirilowii gummy stem blight pathogen.Based on previous studies,experiments were designed to induce sporulation of S.citrulli in melon and T.kirilowii under 9 different media.It was screened that conidia were successfully induced on yeast extract-PDA medium,melon and T.kirilowii juice（diluted5x and 50x）calcium carbonate medium supplemented with UV-induction conditions,and ascospores were produced under UV-induced conditions in oat medium.The conidia of S.citrulli,the pathogen of gummy stem blight of melon and T.kirilowii,were short round to cylindrical,with blunt rounded ends,colorless,average size of 5.6μm×3.0μm,single cell;The ascospores in the pseudocyst shell were clavate,colorless and transparent,with blunt rounded tips,containing 8 ascospores;The ascospores were colorless and transparent double cells,oval,with a septum laterally,and the septum was obviously constricted at the septum to divide the spores.The upper cell was wider and blunt at the tip,and the lower cell was narrower,and the average size of ascospores was 12.85μm×5.7μm.3.Biological characteristics of S.citrulli of melon and T.kirilowii.In this experiment,the optimum growth p H,the utilization of carbon and nitrogen sources,and the lethality temperature of conidia were determined.The results showed that the optimum growth p H for mycelium of melon and T.kirilowii was 7.0,and the mycelium grew best when soluble starch,maltose and fructose were used as carbon sources.When the nitrogen sources were peptone,asparagine and ammonium dihydrogen phosphate,the mycelial growth was the best.The lethal temperature of conidia was 50°C for 10 min.4.Screening of effective fungicides against S.citrulli of melon and T.kirilowii.In this study,the inhibitory effects of seven fungicides on the mycelial growth of S.citrulli in melon and T.kirilowii were determined.The results showed that the inhibitory effects of mifenamide and boscalid on S.citrulli in melon and T.kirilowii were the best,with EC₅₀values ranging from 0.0106 to 0.0438μg/m L,followed by isoxaflutole and phenoxymethoxazole,with EC₅₀values ranging from 0.8675 to 1.7675μg/m L.The inhibitory effect of carbendazim was the worst,with EC₅₀values of 40.6777μg/m L.