深州蜜桃黑斑病（Alternaria　alternata）的研究Ⅱ．侵染规律和发病诱因

Study on Occurrence of Peach Black Spot (Alternaria alternata) and Disease Disposition

桃树健康和枯死组织普遍带有链格孢，枯死组织带菌率更高。病菌侵染果实主要在盛花期至盛花后约４０ｄ这段时期，侵染高峰在花萎期（４月下旬）。空中孢子捕捉试验证明，当气温稳定在２０℃以上时（５月中旬以后），雨后空中孢子迅速增长，此期空中孢子量与侵染高峰有密切关系。密植树、幼树发病较轻、树下部发病较轻，６月中旬以后套袋对黑斑病发病率无明显影响。

A peach tree, either healthy tissues or withered tissues widely carry Alternaria alternata, especially withered tissues, of which the rates of carrying fungi are most high. The fungus infects fruits mainly at full-bloom stage or about 40 day after full-bloom. During this period,the peak of infection is at stage of flower wilting (during the later ten days of April). It have been indicated through the experiment of collecting spores in the air that number of spores in the air increase rapidly after rain and when the temperature is steadily above 20℃ (after the early ten days of May). At this stage, the number of spores in the air have close relations with the peak of infection. Closed planted trees, young trees have light disease incidence and so do the lower parts of trees. After middle of June, covering fruit with paper bag do not decrease obviously the disease rate of black spot.