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在北京和天津等地调查研究了大白菜霜霉病的初侵染来源问题,并对幼苗的有限系统侵染现象进行了研究。卵孢子是初侵染的重要来源,华北和东北各主要白菜产区的白菜病叶和菜田土壤中存在有大量霜霉病菌的卵孢子。这些卵孢子可以侵染幼苗而引起发病,在田间形成初发病株成为再侵染的来源。田间卵孢子一年不止形成一次,春菜上形成的卵孢子到秋季即可侵染。种子带菌情况因地区而异。山东“胶州白”因种株上易罹病害,莢果组织中的卵孢子可以夹在种子间传播。1961—1962年在京津两地收集的种子上未检查到卵孢子。唯在部分春播采种的种子上,病菌菌丝可潛伏于种皮中并产生孢子囊。以菌丝在留种株上潛伏而在次年带到田间成为春菜初侵染来源的可能性仍需进一步研究。首次报导了大白菜幼苗上 Peronospora parasitica 的有限系统侵染可以达到第一对真叶。病菌从茎基部侵入后,菌丝向上扩展进入子叶和第一对真叶,但不进入第二对真叶。田间最早发生的病株大多是有限系统侵染的。这一发现对了解病害流行起点是有帮助的。
The primary sources of downy mildew in Chinese cabbage were investigated in Beijing and Tianjin, and the limited systemic infection of seedlings was studied. Oospora is an important source of primary infection. There are many oospores of downy mildew in cabbage leaves and vegetable soils in the major cabbage producing areas of North and Northeast China. These oospores can infect young seedlings and cause disease, forming the initial strain in the field as a source of re-infection. Field oospores formed more than once a year, the spring spawn on the formation of oospores can be infected in the fall. Seed-borne conditions vary by region. Shandong “Jiaozhou white” because of the strain susceptible to diseases, pod tissue in the oospores can be sandwiched between the seeds spread. Oocysts were not detected on the seeds collected in Beijing and Tianjin between 1961 and 1962. Only part of the spring planting seed, the mycelium of bacteria can be latent in the seed coat and produce sporangia. The potential for mycelium to stay dormant in the mycelium and bring it to the field in the following year becomes a source of early spring apricot remains to be further studied. It was first reported that limited systemic infection of Peronospora parasitica on Chinese cabbage seedlings can reach the first pair of true leaves. After the bacteria invaded from the base of the stem, the mycelium expanded upward into the cotyledon and the first pair of true leaves, but did not enter the second pair of true leaves. Most of the diseased plants in the field were mostly infected by the limited system. This finding is helpful to understand the starting point of a disease.