Study On The Biological Characteristics Of Alternaria Alternata Japanese Pear Pathotype And Its Bio-Chemical Control Technique

Pear black spot is one of the major disease in fruits and spreads worldwidle. It occurrs seriously in Asia and prevents pear export in recent years. In order to control pear black spot, the research firstly, we studied the biological characteristics and pathogenicity of Alternaria alternata Japanese pear pathotype strains, secondly appraised the resistance of the different pear varieties on pear black spot, thirdly, screened the best bio-control strains and fungicide against Alternaria alternata Japanese pear pathotype in vitro, and composited this fungicide with E-29 in a good proportion. Lastly, studied the control effect of the compound fungicide in field. All the results were as follows:(1) Pear black spot samples were obtained from pear garden of Jiangsu Academe of Agricultural Sciences in 2003, and 24 Alternaria alternata Japanese pear pathotyope strains were isolated and identified.There were different significantly in growth characteristics (including: growth rate, quality of spore, color of colony and thickness of colony) in PSA media. The optimum temperature for mycelia growth was 28℃; the optimum temperature for spores germination was 28℃. The optimum relative humidity of mycelia growth was 98-100%; only under high relative humidity condition, the spores could germinate; especially in water drop, the germination rate of the spores is highest. The optimum pH value for mycelia growth was 7-8. The pH value of PSA could be changed by Alternaria alternata after culturing. The optimum pH value for spores germination was 7-8. Alternaria alternata could use many carbohydrates and nitrogen sources, the optimum carbon and nitrogen sources were sucrose and peptone respectively, while (NH₄)₂SO₄ and NH₄CL would inhibit mycelia growth.Under expremental condition, the characteristics of spore and colony of Alternaria alternata Japanese pear pathotyope changed with time. We distilled DNA of 24 strains, and expanded sequences of 18 strains, the phygenitic tree showed there was different among 8 strains by DNAstar.