Identification Of Pathogen Causing Pear Abnormal Defoliation And Screening Of Tolerant Cultivars

Abnormal defoliation in pear plant at early autumn has become a problems and attracted wide attention in pear production.The situation is even more serious in the southern parts of pear producing areas in China,which is mainly caused by anthracnose.As a pear plant disease worldwide,anthracnose can infect different hosts and do harm to fruits,leaves and branches of many species of fruit trees.The samples of leaf with anthracnose symptom were taken from the pear orchard in Dangshan County,Anhui Province,China.The pathogens were isolated from the diseased parts,their morphological characteristics and growth characteristics were observed,and then,the five genes i.e.ITS,ACT,CAL,GAPDH,and TUB2 were amplified and sequenced.A phylogenetic tree was constructed using unweighted pair-group method with arithmetic means(UPGMA)with each sequence of the five genes and their concatenated sequence data to determine the species of pathogenic bacteria.The potted one-year-old pear plants of 34 cultivars were used for screening of tolerant variety.The conidia suspension of the fungus was sprayed on the leaves to induce the symptoms of the diseases.According to the incidence of the disease,the observed data were analyzed in order to obtain cultivars resistant to anthracnose.The main results were obtained as follows.(1)In view of the wide species of Colletotrichum gloeosporioides complex,the species cannot be identified accurately by the morphological characteristics.Multiple loci gene cluster analysis combined with the morphological characteristics demonstrated that the pathogenic species belong to Colletotrichum fructicola.(2)The results showed that the pear anthracnose incidence occurred in different cultivars were quite different.The symptom induced was lighter in the early and severe in the late stage.With the passage of infection time,the incidence become more serious and the diseased leaves began to fall off.Among the tested cultivars in the study,’Whangkeumbae’,’Cuiyu’,and ’Yuguan’ pear belonged to anti-anthracnose cultivars,’Kosui’pear and other 10 cultivars were the semi-anti-anthracnose,’Meirensu’ pear and other 5cultivars were moderate,’Cuiguan’ pear and other 10 cultivars were semi-sensitive,and’Zaosu’ and other 6 cultivars were susceptible according to the statistic results by disease index.(3)Based on the research result,3 cultivars of Anthracnose Resistant,such as’ Whangkeumbae’,and 10 cultivars such as ’ Xing Shui ’,which are available for popularization,are relatively resistant to anthrax.