Identification And Pathogenicity Of Diaporthe Species Causing Shoot Blight And Leaf Spot Of Kiwifruit

Diaporthe species are important pathogens with comprehensive host associations and geographic distributions,relevant with severe diebacks,cankers,leaf spots,blights,decay and stem-rot of fruits in several different crops.In recent years,shoot blight and leaf spot diseases of kiwifruit are widespread and prevalent;these diseases pose a greater threat to kiwi yield and quality.Therefore,there is an urgent need to solve this problem in production.This study investigated the occurrence and damage of branch blight and leaf spot in the main cultivation areas of kiwifruit in China,and collected disease samples to isolate pathogens.The combination of morphology and multi-locus phylogenetic analysis was used to identify the pathogens species that cause branch blight and leaf spot disease in the main production areas of kiwifruit,and verified by Koch's postulates.This study provide reliable theoretical basis for the effective prevention and control of the disease.1)Identification of Diaporthe species causing kiwifruit branch blight and leaf spotDuring the period of 2017-2019,extensive investigations were conducted on the occurrence and damage of branch blight and leaf spot of Actinidia chinensis and Actinidia deliciosa grown in nine main kiwifruit-production provinces in China,including Anhui,Chongqing,Fujian,Hubei,Henan,Shanxi,Shandong,Sichuan,and Zhejiang.A total of 106 diseased leaf and branch samples were collected from 10 cultivars,and 350 isolates were derived from these diseased samples,according to the colony morphology and conidia characteristics,283 strains belong to Diaporthe,of which 82 were isolated from leaf spot and 201 were derived from leaf spot.The morphological characteristics showed that the colony color and aerial mycelium morphology of representative strains are quite different.In addition,the morphological characteristics are susceptible to change due to the influence of the cultivation environment.Therefore,it is difficult to identify species based solely on morphological characteristics.Based on the preliminary morphological observation and sequence analysis of EF1-? gene of 283 Diaporthe strains,44 representative strains were selected for multi-locus(ITS,EF1-? and TUB2)phylogenetic analysis.The results showed that these 283 strains belonged to 7 species of Diaporthe,including D.unshiuensis(100 isolates),D.eres(94 isolates),D.sojae(57 isolates),D.hongkongensis(19 isolates),D.compactum(5 isolates),D.alangii(5 isolates),D.tectonae(2 isolates).The results of pathogen isolation showed that the species of pathogens were different among the isolated tissues.Six species(D.unshiuensis,D.eres,D.sojae,D.compactum,D.hongkongensis,and D.alangii)were isolated from leaf spot;seven species(D.unshiuensis,D.eres,D.sojae,D.hongkongensis,D.compactum,D.alangii,and D.tectonae)were isolated from branch blight.However,D.unshiuensis,D.eres,and D.sojae these three species own the highest isolate ratio,the proportion of isolation was 42.79%,31.34%,14.93%(branch blight)and 37.80%,32.93%,17.07%(leaf spot),respectively,which indicated that these three Diaporthe species were the main pathogens causing the branch blight and leaf spot of kiwifruit.This is the first report of seven Diaporthe species related to kiwifruit in China.2)Pathogenicity of seven Diaporthe species isolated from kiwifruitThe pathogenicity of 14 representative strains selected from seven Diaporthe species was determined.Pathogenicity tests were performed on detached leaves of Actinidia chinensis cv.Cuiyu and the fruits of A.deliciosa cv.Hayward as well as the branches of A.chinensis cv.Hongyong,A.chinensis cv.Jinyan,A.chinensis cv.Cuiyu,A.chinensis cv.Huangjin.The pathogenicity tests results showed that,leaves,branches,and fruits of the cultivars are sensitive to representative isolates of the seven Diaporthe species,but the virulence of these species differed.The pathogenicity of D.alangii and D.tectonae were significantly higher than that of D.unshiuensis,D.eres,D.sojae,D.hongkongensis,and D.compactum.The host range assessment was performed on the vitro branch of Pyrus Linn,Prunus persica Sieb.et Zucc,Prunus armeniaca L.,Prunus salicina L.and Malus pumila Mill.The results showed that representative isolates of seven species could cause lesions on most fruit tree pertain to the Rosaceae family.However,there are significant differences in the pathogenicity of the inoculated plants.