在農業上,對付病蟲害,通常是用化學殺蟲或殺菌劑施於已生長的植物上來防除的。可是許多種植物的病害——如小麥的腥黑穗病,棉花的紅腐病、炭疽病和立枯病等,係植物種子在種植前已先有病原菌的寄生;這種不健康的種子種植後便成爲病害的由來。這樣被害的農作物,每年的數量非常大;例如,腥黑穗病在山東一省就有50—70％ In agriculture, dealing with pests and diseases is usually controlled by applying chemical insecticides or bactericides to the growing plants. However, the diseases of many kinds of plants, such as wheat’s tangled ears, red rots of cotton, anthracnose and blight, are the first to have the parasites of pathogenic bacteria before planting. After the unhealthy seeds are planted It has become the origin of the disease. The number of such crops is very large every year; for example, there is 50-70% of fish head smut in Shandong Province,