手机知网 App
24小时专家级知识服务
打 开
手机知网|搜索

Identification and characterization of Phytopythium helicoids causing stem rot of 'Shatangju' mandarin seedlings in China

Xiaoren Chen;Beibei Liu;Yuping Xing;Baoping Cheng;Yunhui Tong;Jingyou Xu

  Citrus mandarin(Citrus reticulata) cultivarShatangjupossesses great economic importance in southern China because of its delicious fruits and medicinal peels.During surveys conducted in 2012 and 2013,a stem rot disease were observed on graftedShatangjuseedlings in 21 nurseries located in three regions(Yangjiang City,Sihui City and Deqing County) of Guangdong Province,China.The aim of this study was to characterize the symptoms of seedling stem rot;evaluate the incidence and loss;identify the causal agent and evaluate its pathogenicity and virulence.The disease was present in all surveyed nurseries but incidence varied with location.A Pythium-like oomycete species was consistently obtained from symptomatic plants collected in the nurseries surveyed.On the basis of morphological and cultural characteristics and combined phylogenetic analysis of four molecular barcodes including the internal transcribed spacer region(ITS),β-tubulin,mitochondrial CoxⅠ and CoxⅡgenes,20 isolates obtained were identified as belonging to the species Phytopythium helicoids.Two representative isolates were pathogenic to the scions but rootstocks of Shatangjumandarin seedlings cultivated under nursery conditions and in a greenhouse and symptoms identical to that observed in the field were reproduced.The pathogen was reisolated consistently from the inoculated plants,confirming Koch s postulates.Seedling stem rot and death caused by P.helicoids represents a serious threat toShatangjumandarin nurseries productivity and longevity in southern China.……