Downy mildew of spinach, caused by the obligate pathogen Peronospora effusa, remains the most important constraint in the major spinach production areas in the United States. This disease can potentially be initiated by asexual sporangiospores via “green bridges”, sexually derived oospores from seed or soil, or dormant mycelium. However, the relative importance of the various types of primary inoculum is not well known. The ability of P. effusa sporangiospores to withstand abiotic stress, such as desiccation, and remain viable during short- and long-distance dispersal and the ability of oospores to germinate and infect seedlings remain unclear. Thus, the primary objectives of this research were to evaluate the impact of desiccation on sporangiospore survival and infection efficiency and examine occurrence, production, and germination of oospores. Results indicate that desiccation significantly reduces sporangiospore viability as well as infection potential. Leaf wetness duration of 4 h was needed for disease establishment by spinach downy mildew sporangiospores. Oospores were observed in leaves of numerous commercial spinach cultivars grown in California in 2018 and Arizona in 2019. Frequency of occurrence varied between the two states-years. The presence of opposite mating types in spinach production areas in the United States was demonstrated by pairing isolates in controlled crosses and producing oospores on detached leaves as well as intact plants. Information from the study of variables that affect sporangiospore viability and oospore production will help in improving our understanding of the epidemiology of this important pathogen, which has implications for management of spinach downy mildew.

由专性病原体Peronospora effusa引起的菠菜霜霉病仍然是美国主要菠菜产区的最重要制约因素。该疾病可能是由无性孢子囊孢子通过“绿色桥”，来自种子或土壤的有性卵囊孢子或休眠菌丝体引发的。但是，各种类型的原种接种物的相对重要性尚不清楚。P. effusa的能力孢子囊孢子能够承受诸如干燥的非生物胁迫，并且在短距离和长距离扩散过程中仍保持活力，卵孢子发芽和感染幼苗的能力仍不清楚。因此，这项研究的主要目的是评估干燥对孢子囊存活和感染效率的影响，并检查卵子的发生，产生和萌发。结果表明，干燥明显降低了孢子孢子的活力以及感染潜力。菠菜霜霉病孢子囊孢子病的发病需要叶片湿润时间为4小时。在2018年在加利福尼亚州和2019年在亚利桑那州种植的许多商业菠菜品种的叶片中均观察到了卵孢子。在两个州年之间，其发生频率各不相同。通过在控制的杂交中配对分离株并在离体的叶子以及完整的植物上产生卵孢子，证明了在美国菠菜生产地区存在相反交配类型。从影响孢子囊活力和卵子产生的变量的研究中获得的信息将有助于增进我们对这种重要病原体的流行病学的了解，这对菠菜霜霉病的治理具有重要意义。