Department of Plant Pathology and Plant-Microbe Biology, Cornell Unviversity, New York State Agricultural Experiment Station, Geneva, NY 14456, USA.
Phytopathology. 2010 Mar;100(3):246-51. doi: 10.1094/PHYTO-100-3-0246.
A collection of four clonal isolates of Podosphaera aphanis was heterothallic and was composed of two mutually exclusive mating types. Cleistothecial initials approximately 20 to 30 microm in diameter were observed within 7 to 14 days after pairing of compatible isolates and developed into morphologically mature ascocarps within 4 weeks after initiation on both potted plants maintained in isolation and in field plantings in New York State and southern Norway. Ascospores progressed through a lengthy maturation process over winter, during which (i) the conspicuous epiplasm of the ascus was absorbed; (ii) the osmotic potential of the ascospore cytoplasm increased, resulting in bursting of prematurely freed spores in water; and, finally, (iii) resulting in the development of physiologically mature, germinable, and infectious ascospores. Release of overwintered ascospores from field collections was coincident with renewed plant growth in spring. Overwintered cleistothecia readily dehisced when wetted and released ascospores onto glass slides, detached strawberry leaves, and leaves of potted plants. Plant material exposed to discharged ascospores developed macroscopically visible mildew colonies within 7 to 10 days while noninoculated controls remained mildew free. Scanning electron and light microscopy revealed that cleistothecia of P. aphanis were enmeshed within a dense mat of hyphae on the persistent leaves of field-grown strawberry plants and were highly resistant to removal by rain while these leaves remained alive. In contrast, morphologically mature cleistothecia on leaves of nine deciduous perennial plant species were readily detached by simulated rain and seemed adapted for passive dispersal by rain to other substrates. Contrary to many previous reports, cleistothecia appear to be a functional source of primary inoculum for strawberry powdery mildew. Furthermore, they differ substantially from cleistothecia of powdery mildews of many deciduous perennial plants in their propensity to remain attached to the persistent leaves of their host during the intercrop period.
四个无性系 Podosphaera aphanis 的克隆分离物是异宗配合的，由两个相互排斥的交配型组成。在相容分离物配对后 7 至 14 天内观察到直径约 20 至 30 微米的闭囊壳初始物，并在隔离的盆栽植物和纽约州和挪威南部的田间种植中启动后 4 周内发育成形态成熟的子囊壳。在冬季，经过长时间的成熟过程，分生孢子进行了成熟过程，在此过程中：（i）子囊内的明显外质体被吸收；（ii）孢子细胞质的渗透势增加，导致过早释放的孢子在水中破裂；最后，（iii）导致生理成熟、可萌发和具有感染力的分生孢子的发育。田间采集物中越冬分生孢子的释放与春季植物生长的恢复同时发生。当湿润时，越冬的闭囊壳很容易开裂，并将分生孢子释放到载玻片、草莓离体叶片和盆栽植物叶片上。暴露于排出的分生孢子的植物材料在 7 至 10 天内发展为肉眼可见的霉斑菌落，而未接种的对照则保持无霉斑。扫描电子显微镜和光学显微镜显示，P. aphanis 的闭囊壳被纠缠在田间生长的草莓植株持久叶片上的密集菌丝层中，并且在这些叶片仍然存活时，对雨水的去除具有高度抗性。相比之下，在九个落叶多年生植物物种叶片上形态成熟的闭囊壳很容易被模拟雨水分离，似乎适应通过雨水被动传播到其他基质。与许多先前的报道相反，闭囊壳似乎是草莓白粉病的主要接种源的功能来源。此外，与许多落叶多年生植物白粉菌的闭囊壳相比，它们在作物间期间保持附着在其宿主持久叶片上的倾向有很大不同。
