水稻纹枯病(Pellicularia sasakii (Shirai) Wei)菌丝的活动与病害发生的关系

纹枯病菌絲在田間稻株上的消长受水稻各生育期、及当时气候条件影响很大;一般在孕穗职前菌絲量少,孕穗至乳熟初期分布量大、蔓延速度快;抽穗期后10天达到最高峯。早稻成熟期菌絲停止蔓延或消失;晚稻(尤其連作晚稻)抽穗期后因寒潮或低温而停止蔓延;乳熟期趋于消失。纹枯病菌核的发育一般要通过四个时期,无休眠期。病情的水平扩展速度以孕穗至抽穗期最快,乳熟期几停止;而垂直扩展速度以水稻分蘖期最慢,抽穗至乳熟期最快。矮稈品种2—3天,高稈品种3—5天便可士升一个叶位,乳熟后緩慢。晚稻則以抽穗期最快,抽穗后緩慢,乳熟后病势停滞不前。在水稻易感期(孕穗—抽穗),遇到梅雨的两端低温,职及矮稈品种、多肥、密植,在一定有效菌核量下,是本病流行期、流行程度的关鍵因素。防治适期应以菌絲蔓延前期,卽在分蘖期至孕穗期施药,以杀伤菌絲为主;有必要时可在抽穗期再施药一次,保护剑叶,以抑制菌核形成、兼杀菌絲为主。如对矮稈品种、多肥栽培的水稻,于分蘖期施药保护是很必要的。

THE MYCELIAL ACTIVITIES OF THE RICE SHEATH BLIGHT FUNGUS IN RELATION TO THE DISEASE DEVELOPMENT

In the paddy field, the mycelial development of Pellicularia sasakii (Shirai) Wei on the rice plant was closely related to a number of factors especially to the growth stage of the plant and the prevailing climatic condition. Generally, the mycelium developed very scanty before the pregnancy period. Henceforth, the mycelial development was greatly accelerated. The deveIopment reached a maximum at about 10 days before or after the heading. For the early rice varieties the mycelial development ceased at the ripening. For late varieties, it ceased at heading peried owing to the seasonal lowering of temperature in Hunan province. The sclerotial development passed generally four transitional stages being lack of a dorment period. Under the field conditions, the amount of sclerotium developed is directly proportional to the quantity of mycelium alreadly formed. The horizontal spread of the disease was in the stages of pregnancy to heading for early varieties of rice. The vertical spread of the disease was very slow at the tillering stage but accelerated from the heading to milking stages. After which the spread was slowed down porminently. For the late varieties the spread reached a maximum in the heading stage and henceforth slowed down. It is suggested that the effective application of fungicides should be arranged before the accelerated development of the mycelium.