Identification Of The Pathogen Causing Plum Leaf Spot And Biological Characteristics For Monospora Strains From Ascospores

A new disease,called plum leaf spot according to its symptoms,has occured in major plum-cultivation areas of Fujian in recent years and caused a large number of plum leaves to scorch and fall off,which bing very concerned in production.This study carried out the occurrence investigation,symptom observation in field,and sample collection for this disease.The Colletotrichum strains were isolated and identified in order to clarify the pathogenic species composition and dominant ones for this disease.Meanwhile,the culture properties and pathogeneicity for the monospora strains from ascospores of C.fructicola were studied to determine the differences between biological characteristics of different types of monospora generations.The following main findings were obtained:1.Identification of the pathogen causing plum leaf spot.This study carried out the occurrence investigation and symptom observation of plum leaf spot in Liancheng country,Fujian province.The sample with typical symptoms of this disease were collected for pathogen isolation and purification.According to the morphological characteristics of the colony,a total of 69 Colletotrichum strains were obtained.43 representative isolates were selected for morphological observation and phylogenetic analysis based on five loci(ACT,TUB2,CHS-1,GAPDH,and ITS).The results showed that these isolates belonged to 6species of Colletotrichum.Among them,C.pruni-salicinae is a novel species identified in this study.C.fructicola,C.siamense,C.wuxiense,C.karstii and C.plurivorum are known species.Except for C.siamense,the others were isolated from plum for the first time.The statistical results of the number of pathogen obtained showed that the ratio of C.fructicola was the highest(89.9%)among the above 6 species of Colletotrichum,The pathogenic test results show that,the inoculation of 10 representative strains of the above 6 species of Colletotrichum could make plum pathogenic,the symptoms are basically the same as those in the field.However,there are differences in the pathogenicity between different species and different source strains of the same species.The above results showed that,the 6 species of Colletotrichum identified in this study were the pathogens and C.fructicola was the most dominant.2.Studies on biological characteristics for monosporal generations from ascospores of C.fructicola.The dominant pathogen FRL-3-1 strain of C.fruticola was selected for isolation and culture of ascospore monospore.FRL-3-1 strain of C.fruticola was selected for isolation and culture of ascospores The results showed that C.fructicola could generate two types of monospora strains with different morphological characteristics,which were called "plus" and "minus" monospora strains respectively.The hyphae of plus monospora strains were white and the aerial hyphae are developed;the hyphae of minus monospora strains were grey-black and the aerial hyphae were undeveloped.The separation ratio of minus monospora strains(93.7%)was significantly higher than that of plus monospora strains(6.3%).The results of mycelial growth rate and pathogenicity showed that the growth rate of plus monospora strains was faster than that of minus monospora strains and the pathogenicity was stronger than that of minus monospora.The perithecia were observed in both plus and minus colonies by culturing separately.Perithecium were produced at the junction of colonies by confronting each other.The results showed that monospora strains from ascospores of C.fructicola can be either homothallism or heterothallism.In this study,the species of Colletotrichum and dominant pathogenic ones causing plum leaf spot in Fujian were determined.One new specie of Colletotrichum was described and plum were identified as the new hosts of four species of Colletotrichum.It was found that there were significant differences in the biological characteristics of the plus and minus monospora generations from ascospores of C.fructicola.The results supply a theoretical basis for controlling plum leaf spot in the production areas,and provide new useful information for understanding the diversity of species and pathopoiesis of Colletotrichum fungi.