The Study On The Infection Pattern And Genetic Diversity Of Valsa Mali In Hebei

Infecting through various kinds of wounds on the tree, Apple Valsa canker [Valsa mali]almost occurs in all production areas of China. It is so difficult to be controlled as to resultin serious economic losses.The study on infection period and canker extension was conducted in this thesis inorder to clarify the infection pattern. Field tests were carried out to determine the role ofpruning tools in dispersal of V. mali. The genetic diversity, biological characteristics andpathogenicity of different V. mali isolates collected from Hebei province were also studied.The main results of the above experiments are as follows:1. Results of the infection period tests suggested that V. mali could keep infectingduring the whole year, and the infection rates formed in spring and summer were higher.The results also showed that the fresh wounds were easier to be infected by V. malicompared with the old ones.2. The lesions length and width and the limb diameter were measured periodically, theresults indicated that the canker could extend all over the year. While the leision monthlyextension varied significantly. The vertical extension peak occurred in April, while thehorizontal extension appeared two peaks, April and November.3. From December2011to November2012, pycnidia collected from the same cankerlesion monthly to detect the conidia production. The results suggested that the conidiacould be produced every month in a year, while the biggest conidia production numberappeared in May, following by December.4. The pruning experiments were conducted in the middle of each month fromDecember2011to March2012and from November2012to March2013. Use the saw withthe conidia of V. mali to make a wound on the trunk of40trees each month, and record theincidence. The results indicated that the pruning tools with V. mali could spread thisdisease, and the incidence from November to February was higher than March. As a result,pruning in spring especially in March instead of winter time could reduce the spread andinfection of V. mali.5. The study of biological characteristics and pathogenicity of different isolates of V. mali in Hebei province indicated that there were significant difference in colony color,colony growth rate and colony density between different isolates. The pathogenicity ofisolates with different colony color was significantly different. Pale yellow and incanuscolony isolates had strongest virulence when the colony growth rates were similar. Thecolony growth rate was positively correlated with the pathogenicity when the colony colorwas the same. While, there was no correlation between the colony densities and thepathogenicity.6. The genetic diversity of different isolates of V. mali in Hebei province by RandomAmplified Polymorphic DNA (RAPD) suggested that there were89bands amplified andthey were all polymorphic(100%). By using NTSYS2.1, the44isolates were clustered7groups based on the threshold of the genetic distance which was0.72, indicated that V.mali isolates were diverse in Hebei province. However, there was no direct relationshipbetween the genetic groups divided by RAPD and their geographic origins. As a result, wehave chosen seven isolates from the Ⅰ-Ⅶ group, numbered SJZ7、CZ5、XT3、QHD17、HS2、TS8and LF8, as the backup strains for the disease-resistant germplasm materialtesting in the future.