Study Of Pathogen Diversity And Antagonistic Bacteria Of The Causative Agent Of Apple Tree Canker In Gansu Province

Apple tree valsa canker is a stem disease, which is endemic in most of the apple production areas in Gansu. Disease rate is about 40%, seriously restricting the development of apple industry in Gansu province. In this project the species causing the disease in Gansu province as well as the pathogenetic diversity, was studied. Also,antagonist bacterium and culture optimization to control the causative agent of apple tree canker were studied. The main results were listed as follows.1. The pathogen species that cause the apple tree valsa canker in Gansu province were determined on the basis of morphological observation and multiple genes identification. Two species were identified: viz. Valsa malicola(the anamorph was Cytospora schulzeri)and Valsa mali(the anamorph was Cytospora sacculus).2. The Valsa mali can be divided into two varieties below the rank of species level through multiple gene sequence and phylogenetic analysis; the two varieties were Valsa mali var. mali and Valsa mali var. pyri. Valsa mali, particularly the Valsa mali var. mali, was the predominant pathogen of apple valsa canker in Gansu..3. Thirty five ISSR primers were screened and six polymorphic primers were selected to study the genetic diversity of 39 isolates from Gansu province. A total number of 67 polymorphic loci were detected. Sixty six loci were polymorphic loci in the isolates of Valsa mali(polymorphic loci percentage was 98.51%) and 57 loci were polymorphic loci in the isolates of Valsa malicola(polymorphic loci percentage was85.07%). The polymorphic loci were 66 and 30 in the isolates of Valsa mali var. mali and Valsa malii var. pyri(polymorphic loci percentage was 98.51% and 44.78%,respectively).4. The results of genetic diversity of different the species and varieties showed that Nei’s(1973) gene diversity index(H) and Shannon’s information index(I) were both greater than 0.2 and 0.3 respectively, which indicated that that the genetic diversity of the species and varieties was abundant.5. The results of genetic diversity of different geographical groups showed that the dendrogram of different populations was not associated with the geographic origin;therefore polymorphic loci of different geographical groups were different. The polymorphic loci were 38 and 67 in the geographical groups of Ⅰ and Ⅱ, the polymorphic loci percentage were 56.72% and 100%, respectively.6. The antagonistic effects of bacteria strain TS-1203 on the apple tree valsa canker disease fungi was tested by response surface methodology basing on single factor tests. The optimal culture conditions of the bio-control strain TS-1203 were determined for 8 g beef extract, 5 g yeast extract, 10 g glucose, 1000 m L distilled water; temperature at 28.5 o C, p H 9.0, inoculation amount of 6.00%, liquid volume of65 m L/150 m L, the incubation time of 48 h, speeding at 180 r/min. The media used to grow the bacteria was used in the bio-control assays; the inhibition effect of TS-1203 was 94.14% when compared to controls..