The Study Of BTH-Induced Resistance To Alternaira Alternata F.sp.mali In Apple

Alternaira alternata f.sp.mali (AAM) is a most important epidemic disease that threatens the yield and quality of apple production. Currently, the research about AAM is just around biological character of pathogen and the chemical prevention of the disease. Considering the advance of research on induced disease resistance and the characteristic of plant activator, the effects of resistance induced by benzothiadiazole (BTH) at different concentrations against AAM in apple were investigated. The duration of induced disease resistance were studied. Moreover the histopathological mechanism and physiological mechanism were researched. The physiological mechanism comprised the relationship of BTH induced disease resistence with the contents of hydroxyproline-rich glycoprotein (HRGP) and Lignin, with the activity of phenylalanine ammonialyase (PAL), chitinase andβ-1, 3-glucanase.The AAM was isolated and purified from infected apple leaves by tissue isolating method. The conidiophores and mycelia structure of the pathogen were observed by microscope. The pathogenic power was investigated by leaf in vitro inoculation. Apples were inoculated with spores of AAM after applying BTH as a foliar spray to peak branch and disease index was investigated. The histopathological response was investigated with whole leaf clearing and staining technique. The activities of enzyme and the contents of Lignin and HRGP were measured with colorimetric method. The inhibitory effects of different concentration BTH against AAM on potato dextrose agar were studied.The result showed that application of BTH at different concentrations on apple leaves had significant effect to restrain AAM. The effect of 150μg·mL-1 was distinctly better than others, and it could reduce the disease index from 26.34 to 16.87. In addition, the induced disease resistance could last more than 15 days, but the best induced times were 3～6 days after 150μg·mL-1 BTH treatment. However, conidiophores germination and mycelia growth were not restricted by BTH itself. The penetration pegs'formation of pathogen was inhibited, and then pathogen extending was restricted. The activities of PAL, chitinase andβ-1, 3-glucanase of apple leaf rised after BTH inducement. Moreover, the contents of Lignin and HRGP of apple leaf increased too. So the defendable reaction of induced apple trees was started earlier than control.