Identification And Infectivity Characteristics Of Alternaria Causing Moldy Core Of Apple

Moldy core is an important disease on apple fruit.It occurs in all apple producing areas in our country.The infection can cause quality and output decrease,drop prematurely.So this disease causes serious economic loss to growers.Moldy core caused by kinds of fungi.Alternaria is one of the important pathogenic fungi.It is difficult to identify the species of Alternaria because of the highly diversity of species,morphological variation.Recently,a new standard for the identification of Alternaria was established in our laboratory,and we will identify the pathogenic Alternaria of moldy core based on this standard.Secondly,exact periods of infection with Alternaria is unclear.It is one of reasons not to manage moldy core efficiently.In this study,we will carry out systematic identification to pathogenic Alternaria causing apple mordy core,and detect their infection characteristics The main results are as follows:In this study we collected samples from apple main production areas including Shaanxi,Gansu and Henan Province.233 strains were isolated from diseased apples and floral organs.The PGS1 gene was used for the preliminary classification,and 45 representative strains were selected from 10 phylogenetic branches.Based on Alta1-PGS1-APM-CAL-ATP mutilgene sequence combination phylogenetics analysis combined with the pairwise homoplasy index(PHI)of closely related Alternaria species,strains are identified as 5 species: A.alternata,A.daucifolii,A.mordicore(GY Sun & Changkai Niu),A.turkisafria,A.prechina(GY Sun & Changkai Niu).A.mordicore and A.prechina are set as new species.Diversity analysis showed that A.alternata was dominant species and took about 80%.A.daucifolii,A.mordicore,A.turkisafria,and A.prechina accounted for 8%,2%,7.3%,and 2.7%,respectively.A.alternata distributes in wide regions.A.mordicore was only found in Shaanxi,and A.turkisafria only isolated in Gansu from cultivar Red Delicious,and A.prechina from Henan and Gansu.233 strains of Alternaria isolated were detected by PCR amplification using AM-toxin synthetic gene-specific primers,but no one strain can be detected with AM-toxin gene.In this study,the genetic transformation of moldy core host strain ZQ251921 was developed by PEG-mediated protoplasts transformation.15 transformants are obtained.In order to obtain strains labeled by GFP gene having no significant difference in biological characteristics and pathogenicity with the wild type,4 transformants(NC-1、NC-35、NC-50、NC-53)were tested,and 1 transformant(NC-1)were selected for further experiment.Inoculation was carried out by spray spore suspension(NC-1).The results showed that petals,anthers,filaments,and styles,could occur lesions in 24 h after inoculation.The flowers began to fall off on the 4th day after inoculation.After 20 days of inoculation,the pathogenetic young fruit was atrophic,moldy,and shedding.These results show that Alternaria can infect floral organs in the flowering stage and become potential sources of infection associated with moldy core,which provides a theoretical basis for the prevention and treatment in flowering stage.