Identification of the pathogen of peach shoot blight and indoor resistance evaluation of peach varieties (germplasms)

Abstract：【Objective】Peach originated in China and has been cultivated for a long time. In recent years, a shoot blight disease that resulted in brown cankers around buds on shoots or twigs of peach trees has been widely observed in many orchards in Wuxi. This disease could kill shoots and branches and resulted in high yield losses. The study aimed to clarify the pathogens causing peach shoot blight disease and evaluate the disease resistance of the different peach varieties (germplasms).【Methods】 Firstly, a field survey was carried out to determine the incidence of peach shoot blight in peach orchards, and types of symptoms were observed. Secondly, the disease samples were used as materials to isolate the pathogenic fungi by the methods of tissue block separation. The isolates were identified by morphological observation combined with analysis of rDNA internal transcribed spacer (ITS), elongation factor 1-α (EF-1α) and beta-tubulin (TUB) sequences. And the pathogenicity of the isolates wastested based on Koch postulates. Then, wound inoculation method used on detached twigs was used to identify and evaluate the resistance of the 37 peach varieties (germplasms) to shoot blight caused by Diaporthe amygdali. And the system clustering method was adopted to identify the resistance of the different peach varieties (germplasms) to shoot blight based on the disease lesion length data.【Results】 The disease occurred initially on peach shoots and caused brown canker. Subsequently, the reddishbrown cankers developed on the shoots, and resulted in shoot blight, the disease spot presented gummosis sometimes. Total 54 isolates were obtained through tissue separation. All the isolates were identified as 3 species, including D. amygdali (35 isolates), D. eres (5 isolates) and Botryosphaer dothidea (14 isolates) by morphological observation and multiple genes. The result of pathogenicity test showed that the isolates could induce lesions on the shoots, and the pathogens isolated from the infected lesions after inoculation were identical with the inoculated isolates. The resistance determination results indicated that 37 peach varieties (germplasms) were divided into 4 types based on the lesion lengths after 7 d inoculation with D. amygdali isolate by the cluster analysis. Guhetao, Honghuashantao, Zhouxingshantao, Baigengansutao and Honggenggansutao were classified into GroupⅠ. Zhongyoupan No. 9, Zhongyoupan No. 7, Zhongyoupan No. 16, Zhongyoupan No. 13, Honghujing, Hujingmilu, Baihua, Zhongtaohongyu, Wanhujing, Zhongtaoziyu and Qingshuibaitao were classified into Group Ⅱ. Fenghuapantao, Jinghong, Xiahui No. 5, Zhongpantao No. 11, Xiahui No. 6, Yuhualu, Wenzhoushuimi, Xiahui No. 8, Zhanglingzaoyulu, Fenghuayulu, Chaohui, Muyangshuimi, Ri No. 89, Gangshan No. 500 and Yingzuitao were classified into Group Ⅲ. Richuanbaifeng, Liutiaobaifeng, Dazenbaochiyue, Benbaifeng, Fenglu and Baifeng were classified into Group Ⅳ. Guhetao, Honghuashantao and Zhouxingshantao performed as immunity, Baigengansutao and Honggenggansutao performed as resistance, 11 cultivars performed as middle resistant, 15 cultivars performed as susceptibility, and 6 cultivars performed as high susceptibility.【Conclusion】There were three pathogens (D. amygdali, D. eres and B. dothidea) associated with peach shoot blight in Wuxi. D. amygdali was the dominant pathogen of the disease. The different peach varieties exhibited varying degree of resistance to the shoot blight disease from immunity to high susceptibility.