Pathogen Identification Of Guava Fruit Diseases In Yulin City Of Guangxi And Biological Characteristics Research Of The Pathogen Of Black Spot

Guava(Psidium guajava)cv.Watermelon Bar was introduced into Yulin City,Guangxi province in 2015.Black spot disease on fruit was occurred seriously in the field.Four postharvest diseases on fruits were found after being kept at room temperature for 2-3 days,including black rot,anthracnose,ring rot and brown rot.Since Watermelon Bar was a new guava variety introduced to Guangxi,the diseases on fruits were rarely reported.In order to effectively control the guava fruit diseases,identification of the pathogenic species of fruit diseases on Watermelon Bar from Yulin City,Guangxi,research on biological characteristics of the pathogen of black spot were conducted in this article.The typical symptom of guava black spot was black spots on fruits with black dots on the center of lesions.Conidia of pathogen was unicellular,obovate with an appendage.Sequences of ITS,ACT and EF-1α of pathogen were 100% identity to Phyllosticta capitalensis.Phylogenetic analysis results showed that ITS,ACT and EF-1α sequences clustered together with Phyllosticta capitalensis.Based on these morphological characteristics and sequences analysis,the pathogen of guava black spot was identified as Phyllosticta capitalensis,this is the first report of Phyllosticta capitalensis causing black spot on guava in China’s mainland.The typical symptom of guava black rot was brown lesions and rot at the edge of lesions on fruits,with black dots on the center of lesions.Conidia of pathogen was unicellular,nearly fusiform.Sequences of ITS,EF-1α and β-Tub of pathogen were 100% identity to Botryosphaeria dothidea.Phylogenetic analysis results showed that ITS,EF-1α andβ-Tub sequences clustered together with Botryosphaeria dothidea.Based on these morphological characteristics and sequences analysis,the pathogen of guava black rot was identified as Botryosphaeria dothidea,this is the first report of Botryosphaeria dothidea causing black rot on guava in China.The typical symptom of guava anthracnose was reddish brown spots on fruits with orange mucuses and black dots on the center of lesions.Conidia of pathogen was unicellular,cylindrical,obtuse or slightly pointed ends.Sequences of ITS,GAPDH and β-Tub of pathogen were100% identity to Colletotrichum siamense.Phylogenetic analysis results showed that ITS,GAPDH and β-Tub sequences clustered together with Colletotrichum siamense.Based on these morphological characteristics and sequences analysis,the pathogen of guava anthracnose was identified as Colletotrichum siamense,this is the first report of Colletotrichum siamense causing anthracnose on guava in China.The typical symptom of guava ring spot was brown sunken lesions with a yellow ring at the edge on fruits,black dots on the center of the lesions.Conidia of pathogen was nearly fusiform.Sequences of ITS,EF-1α and β-Tub of pathogen were more than 98% identity to Neopestalotiopsis saprophytica,Neopestalotiopsis clavispora,Pestalotiopsis microspora,etc.Phylogenetic analysis results showed that ITS,EF-1α and β-Tub sequences clustered together with Neopestalotiopsis saprophytica.Based on these morphological characteristics and sequences analysis,the pathogen of guava ring spot was identified as Neopestalotiopsis saprophytica,this is the first report of Neopestalotiopsis saprophytica causing ring spot on guava.The typical symptom of guava brown rot was brown water-soaked lesions on fruits with black dots on the lesions.A-conidia oval andβ-conidia curved of pathogen.Sequences of ITS and EF-1α of pathogen were more than 90% identity to Diaporthe melonis and Phomopsis(Anamorph of Diaporthe),including Phomopsis phaseoli and Phomopsis longicolla,etc.Phylogenetic analysis results showed that ITS and EF-1αsequences clustered together with Diaporthe melonis.Based on these morphological characteristics and sequences analysis,the pathogen of guava brown rot was identified as Diaporthe melonis,this is the first report of Diaporthe melonis causing brown rot on guava.Phyllosticta capitalensis was isolated from different healthy tissues of guava,indicating that the fungus was latent infection of guava,which caused guava black spot only at the guava fruits near-mature period.The research results on the biological characteristics of Phyllosticta capitalensis showed that the optimal growth temperature was 32 ℃,the optimal carbon and nitrogen source were glucose and proline respectively,light promoted the mycelia growth.On the four media(GA,PDA,SNA and OA),the mycelia of Phyllosticta capitalensis grew fastest on GA and slowest on PDA.