Molecular Phylogeny Of Plant Pathogenic Fungi Of The Family Mycosphaerellaceae In Southwest China

Mycosphaerellaceae contains thousands of fungal species,many of them are associated with varieties of plant diseases and have great impact on agriculture,horticulture and forestry.Plant resources are abundant in southwest China,but there are few studies on the plant pathogenic fungi of Mycosphaerellaceae,therefore,understanding and clarifying the taxonomy of Mycosphaerellaceae in southwest China is necessary.In this study,over 500 plant specimens with disease symptoms were collected from Guizhou,Sichuan,Yunnan and Guangxi province during 2018 to 2020,from which 44 strains of Mycosphaerellaceae were isolated.According to ITS-BLAST comparison results,these strains belong to the following eight genera:Amycosphaerella(2),Cercospora(6),Epicoleosporium(1),Paramycosphaerella(1),Pseudocercospora(18),Septoria(11),Sphaerulina(3)and Zasmidium(2).Multi-gene phylogenetic analysis combined with morphological analysis was used to identify these strains.A combined dataset of 7 genes(ITS,ACT,TEF,CAL,TUB2,HIS3,RPB2)was used in the phylogenetic analysis of Cercospora.The phylogenetic analysis of Amycosphaerella,Epicoleosporium and Zasmidium were based on 3 genes(ITS,LSU,RPB2),while analysis of Paramycosphaerella and Pseudocercospora were based on 4 genes(ITS,LSU,ACT,TEF).Another combined dataset of 5 genes(ITS,LSU,TUB2,RPB2,TEF)were used in the phylogenetic analysis of Septoria and Sphaerulina.Among the 44 strains,there are 17 species been identified,including9 new taxa(Cercospora yunnanensis,Epicoleosporium nyssae,Pseudocercospora malus,Septoria sanguisorbae,S.pileae,S.longipes,S.disporumae,Sphaerulina celtisus,Zasmidium liboense),8 known species(Amycosphaerella keniensis,Cercospora cf.flagellaris,Cercospora samambaiae,Cercospora manihobae,Paramycosphaerella marksii,Pseudocercospora cotoneastri,Septoria protearum,Zasmidium citri-griseum),and 8 new records in China.In addition,there are 15 strains that cannot be further identified due to lack of morphological features.This is the first study of molecular phylogeny of Mycosphaerellaceae in southwest China,and the conclusions are as follows:(1)Although Mycosphaerellaceae fungi in southwest China is with low detection rate,their richness are relatively high.(2)Protein genes are essential for the taxonomic study of this family,and the primer pair RPB2-F4/f RPB2-7c R plays an important role in the classification and identification of most Mycosphaerellaceae species.(3)TUB2 and TEF1 are the best gene region for identifying Septoria.(4)There are different species of Mycosphaerellaceae on the same host plant,and the same species of Mycosphaerellaceae are found on different host plants,it's inferred that the fungi in this family evolve quickly and have a wide range of hosts.(5)As the detection rate and diversity of Mycosphaerellaceae fungi are different in different regions,it is speculated that the occurrence of Mycosphaerellaceae pathogens are related to the geographical environment.This study provides information for the taxonomic study of Mycosphaerellaceae and is of great significance for the prevention and control of diseases caused by Mycosphaerellaceae fungi.