Study On The Differentiation Of Pathogenicity And Infection Process On Fruits Of Botryosphaeria Dothidea In Shaanxi

Apple Ring Rot caused by Botryosphaeria dothidea (Moug. ) Ces. et De Not. is one of the diseases on trunks and fruits of apple tree, it has occurred in the major apple-producing areas in China in recent years, taking serious affection on the quality and yield of fruits and causing significant economic losses on the agricultural production. At the same time, as the pathogen has the characteristics of latent infection, it has become the important disease during the storage and transportation stages on fruits. Now for the process of the pathogen was unknown and be lack of a fast and stable system to evaluate the pathogenicity, the study on the differentiation of the strains, the selection of resistant materials, the efficacy evaluation and fungicide screening were been constrained, thereby affecting the disease control and prevention research. The study established a rapid, stable and easily operated evaluation system, then using the system to test the pathogenicity of 500 isolates from different regions in Shaanxi, in addition, doing the preliminary study on the infection process of the fungus on the fruit. The major results are as follows:1. Established a fast indoor evaluation system to identify the pathogenicity of B.dothidea by inoculating the excised two years old twigs, current-year shoots, leaves and mature fruits of'Fuji'apple tree with different types of wounds. The research uesd the plugs of the pathogen to inoculate the four excised materials, to compare the lesion sizes of different types of wounds found: lesions formed on the twigs which treated by burning before inoculation were smaller and formed later than others; lesions on the young shoots with one pricking wound were bigger than those on the leaf scars; leaves were easier to be infected by pricking one time on the upper sides than lower sides even with ten times pricking wounds; lesions on fruits inoculated after peeling were bigger than treated with pricking. Furthermore, to prove the results conducted via the methods tested in this study were reliable, four isolates with different virulence were tested through inoculating on both excised materials and shoots in the field. It was showed that all the four excised materials could present the differences in virulence among strains, and the conclusions were consistent with field inoculation on shoots without wound. Therefore, all these four excised materials could be used to evaluate the pathogenicity of B. dothidea accurately and quickly indoor; and excised leaf treated by one-time-pricking on the upper side before inoculation was suggested.2. Clear the differentiation of the pathogenicity of the pathogen in Shaanxi. Inoculated current-year shoots without wound in the field and detached leaves by pricking indoor with 500 isolates, founding that there was differentiation among the pathogenicity of the isolates and there was no obvious relevance between the differentiation and geographical origin. There was clear differentiation of pathogenicity among the 500 isolates from Shaanxi and the group of medium pathogenicity was in the largest proportion. There was general differentiation among the isolates from different regions and the groups of medium pathogenicity had shown some advantages, the isolates from one block also had obvious differentiation, but not yet found there was obvious correlation between the differentiation and geographical origin.3. Clear the infection process of the pathogen on fruit initially. Using the spores suspension to inoculate the fruits and observe the infection process by the electron microscope. Study found that most conidia could germinate around 6 h after inoculation and penetrated the fruit around 9 h after inoculation, the pathogen could penetrated using the germ tube to puncture the lenticel cell directly or from the intercellular. In the diseased fruit, the conidioma was buried under the peel, and there was abundant intercellular and intracellular hyphae in the peel and flesh tissues, especially in the vicinity of the conducting tissues, there were different degree of digestion phenomenon in the diseased flesh tissues. In addition, we also found the presence of hyphae at the transition zone between the health and diseased tissues, indicating the expansion of hyphae was likely earlier than the occurrence of the visible lesions.4. Got a total of 852 isolates by collecting and isolating samples of apple ring rot in Shaanxi and Henan et al, and we found that there were apple ring rot in all the ten countries in Shaanxi and the incidence were different.Through the study of the pathogenicity, it could provide scientific and effective methods on pathogenicity identification and the filter of the resistant materials, lay the basis for the further clarify on the pathogenesis of the disease , and also provided scientific basis for the prevention and control strategy development.