Studies On Biological Characters Andpathogenicity Of Different Isolates Of Cytospora Isolated From Apple Tree

Shaanxi is the main apple-producing base in China. In 2005,the apple cultural area was 5.4×106 hectare, yield was 5.5×106 ton in Shaanxi province. Apple industry had become one of the six important industries of Shaanxi province. Apple industry played an important role in the development of economy and society in Shaanxi. But recently, the apple tree valsa canker caused by Cytospora spp occurred seriously and prevalently, which had became a threaten that held back the apple industry development. The situation of yield losing caused by the pathogens and the prospect of the orchard destroyed by the pathogens had often been seen in the fields. Now, there was no curative fungicide to do with the disease and no apple cultivars were resistant to Cytospora spp. Once the trees were infected by the microbes, the trees restored health very difficultly. The farmers called the disease as apple tree cancer. Because the pathogens could not form fruitbody on normal PDA medium and on normal cultural conditions, the shape and size of fruitbody formed in natural environment varied by host and all kinds of environmental factors affected, by far, the consistent conclusion about the pathogens caused apple tree valsa canker had not achieved, and the characters of pathogens pathogenicity had not know clearly, which deeply affected to know the epidemic rules of pathogens, restricted the development of predicting the breakout and prevalence of disease and identifying the resistance of the host and using it to control efficiently the disease.Therefore, systemic knowing the construct of the pathogens population, and the individual's biological characters and pathogenicity, establishing a kind of technique which could induce the pathogens to produce abundant fruitbody quickly became the primary issues in the work of current disease prevention and treatment. For this reason, seven isolates having different cultural characters on PDA medium were used to study the biological characters, the condition of fruitbody production, and the pathogenicity characters of different isolates in the research. The results were obtained listed as follows:1. The pathogens have different types, which have different biological characters in Shaanxi. The seven isolates could be divided into three types according to the colony colour and biological characters. The milk-white type was isolate with milk-white colony and no fruitbody formation on PDA; the yellow-brown type was isolate with yellow-brown colony on PDA; the taupe type was isolate with taupe colony and producing readily fruitbody on PDA. The milk-white isolate had lower resistance to pH, but higher resistance to high temperature. They grew in pH 4-9 and 5-35℃. The yellow-brown isolates grew in pH 3-9 and 5-35℃. The taupe type had much stronger resistance to pH and temperature, they could grow in pH1 or pH10 extreme acid and alkalescent environment, they also can grow at 38℃while other type isolates...