Differentiation Of Pathogenicity On Branch And Genetic Diversity Of Botryosphaeria Dothidea In Henan

Apple ring rot [Botryosphaeria dothidea (Moug.) Ces.et De Not] is one of three most important diseases in apple production. It has occurred in the major apple production areas in China. The damage of the disease to apple fruits is under control by application of fruit-bags in recent years, whereas the damage to trunks and twigs of apple trees becomes more severe year by year. In this study, the occurrence of Botryosphaeria canker of apple were investigated in major apple production areas in Henan Province and 172 isolates originating from different regions of Henan province were collected and identified . The pathogens of apple ring rot were identified based on morphological characteristics, rDNA-ITS sequences.The pathogenicity of those pathogens were tested by inoculation on twigs of susceptible cultivar"Fuji"and resistant cultivar"Qinguan"and the genetic diversity of pathogen was evaluated by ISSR analysis. The results are as followings:1. The occurrence of Botryosphaeria canker of apple was investigated in 30 orchards in 16 regions of Henan province during July to August of 2007. The results showed that the incidence rate is 8% in a hillside orchard in Lingbao, and 100% in the rest of orchards. The 172 isolates were identified by their morphologic characteristics of colony in PDA and the size of conidia induced in vitro apple shoots. The pathogen was identified as B. dothidea.2. Isolates inoculated on twigs of"Fuji"and"Qinguan"showed that there was differentiation among the pathogenicity to both"Fuji"and"Qinguan"of isolates and the group of medium pathogenicty was in the largest proportion. There was differentiation among the the pathogenicity to both"Fuji"and"Qinguan"of isolates form different hosts, as same as isolates from apple. The cluster analysis of pathogenicty to the two cultivars of isolates founded that the number of medium pathogenic isolates as same as weak pathogenic isolates among population of B. dothidea form Henan province.The group of strong pathogenic isolates was in the least proportion. It was common that there was differentiation among pathogenicity of isolates from the same region. The group of strong pathogenicity was in the largest proportion among population of the pathogen in Luoyang, but the group of medium pathogenicity or weak pathogenicty was in largest proportion in the rest regions. There was no direct correlation between the differentiation and geographical origins.3. The data of the ITS rDNA from selected 17 isolates confirmed those isolates were B. dothidea and they were separated into two haplotypes H1 and H2. The 13 functional ISSR primers collected from 40 ISSR primers generated 88 polymorphic bands within a total of 121 bands and revealed 72% polymorphism and could differentiate all 64 isolates. Their genetic similarities were from 0.44 to 0.99. Two groups of 64 isolates were identified based on their ISSRs. The ISSR group 1 contains 21 isolates, while ISSR group 2 consists of 43 isolates. In this study, it was found that the genetic diversity of B. dothidea isolates was not correlated to their regions, symptoms and tissues of trees. Sixty-four isolates were separated into two ISSR groups, and ISSR Group2 predominated over ISSR Group1 in orchards.The group of weak pathogenicity was in the largest proportion among the ISSR Group1, and the groups of weak pathogenicity was in the largest proportion among the ISSR Group2.The ISSR group 2 including the most of the strong and medium pathogenic isolates.