【背景】白粉病是影响苜蓿产量和品质的主要真菌病害之一，引起紫花苜蓿白粉病的病原有3种：蓼白粉菌(Erysiphe polygoni DC.)、豆科内丝白粉菌(Leveillula leguminosarum Golov.)和豌豆白粉菌(Erysiphe pisi DC.)。【目的】系统研究紫花苜蓿白粉病病原菌的生物学特性，以及分生孢子和闭囊壳的形态特征，明确宁夏地区紫花苜蓿白粉病病原种类。【方法】采用室内盆栽法调查病害发生和闭囊壳形成条件，利用气象站自动获取数据，采用光学显微镜观察病原菌特征，采用水琼脂玻片法观察病原菌分生孢子萌发特性。【结果】紫花苜蓿白粉病发生的温度范围为20?24 °C，湿度范围为40%?60%，形成闭囊壳的条件为温度20?25 °C、湿度70%左右，闭囊壳的形成大约需要42 d。分生孢子以向基式的产孢方式在分生孢子梗上产孢，成熟的分生孢子卵圆形或椭圆形，大小为(29?46)×(12.5?21.0) μm。闭囊壳黑褐色，球形或近球形，直径71?135 μm，具有大量附属丝，少数为不规则分枝1?2次。闭囊壳内含有4?6个子囊，子囊倒棒型或卵圆形，具柄，大小为(58?90)×(29?60) μm。子囊内含有4?6个子囊孢子，子囊孢子单孢，卵圆形或椭圆形，大小为(21?34)×(10.5?20.0) μm。分生孢子萌发的最适温度范围为22?26 °C，最适pH为6.5，光照促进分生孢子的萌发。葡萄糖、D-木糖和甘露醇促进分生孢子萌发和芽管生长，半胱氨酸促进分生孢子萌发，甘氨酸促进芽管生长。【结论】宁夏地区紫花苜蓿白粉病的病原菌确定为蓼白粉菌(Erysiphe polygoni DC.)。
[Background] Powdery mildew is one of the main fungal disease affecting the yield and quality of alfalfa. It has been reported that there are three pathogens causing alfalfa powdery mildew: Erysiphe polygoni DC., Leveillula leguminosarum Golov., and Erysiphe pisi DC. [Objective] The biological characteristics of alfalfa powdery mildew, the morphological characteristics of conidia and cleistothecium were systematically studied, and the pathogenic species of alfalfa powdery mildew in Ningxia were identified. [Methods] The occurrences of the disease and the formation conditions of the cleistothecia were investigated by pot culture in the laboratory. The data were obtained automatically by the meteorological station. The characteristics of the fungi were observed by the light microscope, and the germination characteristics of the conidia of the fungi were observed by the water agar slide method. [Results] The temperature range of alfalfa powdery mildew is 20?24 °C, the humidity is 40%?60%. The conditions for the formation of cleistothecia are 20?25 °C and humidity about 70%. The formation of cleistothecium takes about 42 d. Conidia produce spores on conidiophore in a basipetal form. Mature conidia oval or elliptic, with the size is (29?46)×(12.5?21.0) μm. The diameter of dark brown globular or subglobular cleistothecium is 71?135 μm, with a large number of appendages, and a few are irregular branches 1?2 times. The cleistothecium contains 4?6 asci, oval, with the handle, and the size is (58?90)×(29?60) μm. The ascus contains 4?6 ascospores, which are ascospore monospora, oval and the size is (21?34)×(10.5?20.0) μm. The optimum temperature range of conidia germination is 22?26 °C, the optimum pH is 6.5, and the light could promote conidia germination. Glucose, D-xylose and mannitol promoted the germination of conidia and the growth of bud tube, cysteine promoted conidia germination, and glycine promoted the growth of bud tube. [Conclusion] The pathogen of alfalfa powdery mildew in Ningxia was identified as Erysiphe polygoni DC.