Species Diversity Of Colletorichum Causing Apple Glomerella Leaf Spot In China

Anthracnose is a kind of fungal disease caused by Colletotrichum spp.that significantly impact apple production.The typical symptoms include bitter rot and leaf spot on apple.Glomerella leaf spot(GLS)can cause severe leaf defoliation by harvest under favorable conditions and thus causes serious losses in fruit production and commercial value.GLS is present in regions with humid climate such as southern Brazil,southeastern U.S.A,and China.In China,Glomerella leaf spot is an emerging apple disease in recent 10 years.In the investigation,we found that Colletotrichum species could infect the Crab apple host.The aim of this study is to determine the species constitution of Colletotrichum spp.causing GLS in the main apple-producing areas of China,including Liaoning,Shandong,Guizhou Henan and Shaanxi Provinces,based on pathogen isolation and purification,morphological characterization,molecular phylogenetic analysis and determine the effect of Colletotrichum species from the Crab apple host to Glomerella leaf spot(GLS).The main results were summarized as follows.1.To clarify the pathogens of Colletotrichum causing Glomerella leaf spot(GLS)on apple in China.In the study,a total of 434 samples were isolated from 386 apple leaves samples and 48 apple fruits samples from the main apple-producing areas of China,including Liaoning,Shandong,Guizhou,Henan and Shaanxi Provinces.The Colletotrichum species were identified based on pathogen isolation and purification,morphological characterization and molecular phylogenetic analysis.All isolates were grouped into four species: C.aenigma,C.fructicola,C.siamense and C.gloeosporioides.Through comparison of the pathogens of Colletotrichum in the main apple-producing areas of China.It was revealed C.siamense and C.gloeosporioides were new pathogens associated with GLS.Pathogenicity test showed that four species of Colletotrichum isolates are able to infect apple leaves of cultivar Gala by non wound inoculation.C.aenigma was the predominant pathogen associated with Glomerella leaf spot,occupying 61.75% of the total strains.The isolation rates of C.fructicola,C.siamense and C.gloeosporioides were represented as20.51%,16.13% and 1.61% of GLS samples,respectively.2.The Colletotrichum species could infect Crab apple cause Glomerella leaf spot.A total of 280 samples were collected from Shaanxi and Shandong Provinces in China.172 isolates were identified based on morphological characterization and four genes(ACT,GAPDH,CHS-1 and TUB2)for analysis,All isolates were identified as four species: C.aenigma,C.gloeosporioides,C.kahawae and C.karstii.The pathogenicity test showed that all four species of Colletotrichum isolates are able to infect apple leaves of cultivar Gala by non wound inoculation.C.gloeosporioides was the predominant pathogen from Crab apple,occupying 86.63% of the total strains.The isolation of rates C.aenigma,C.kahawae and C.karstii were represented as 12.21%,0.58% and 0.58% of Colletotrichum samples,respectively.The isolates of Colletotrichum form Crab apple included three new pathogens to Crab apple(C.aenigma,C.kahawae,C.karstii).To our knowledge,this is the first report of four species of Colletotrichum causing Anthracnose on Crab apple in China.The Colletotrichum species from Crab apple could infect apple causing Glomerella leaf spot,are the possible infection sources for apple GLS.