McDonald Mary Ruth, Sharma Kalpana, Gossen Bruce D, Deora Abhinandan, Feng Jie, Hwang Sheau-Fang
Phytopathology. 2014 Oct;104(10):1078-87. doi: 10.1094/PHYTO-07-13-0189-R.
The disease cycle of Plasmodiophora brassicae consists of a primary phase in root hairs followed by a secondary phase in the root cortex and adjacent tissues. However, the role of root hair infection in subsequent cortical infection and development of P. brassicae is not well understood. To examine the role of the primary and secondary stages separately, inoculation studies with resting spores (source of primary zoospores) and secondary zoospores of a virulent and avirulent pathotype were conducted on canola (Brassica napus). The size of secondary zoospores and number of nuclei were also examined. The zoospores were larger (≈9.6 to 14.4 μm) than in previous reports and all were uninucleate. Inoculation with secondary zoospores alone produced both primary and secondary infection, even with the avirulent pathotype. No symptoms developed from inoculation with avirulent primary zoospores but tiny, bead-shaped clubs developed from inoculation with avirulent secondary zoospores. Inoculation with virulent secondary zoospores alone resulted in lower disease severity than inoculation with virulent resting spores alone. The results indicate that recognition of infection by the host and initiation of a response (induction or suppression of resistance) occurs during primary infection, although recognition can also occur during cortical infection and development.
芸苔根肿菌的病害循环包括在根毛中的初级阶段，随后是在根皮层和相邻组织中的次级阶段。然而，根毛感染在芸苔根肿菌随后的皮层感染和发育中的作用尚未得到充分了解。为了分别研究初级和次级阶段的作用，用休眠孢子（初级游动孢子的来源）以及一种致病型和无毒型致病型的次级游动孢子对油菜（甘蓝型油菜）进行了接种研究。还检查了次级游动孢子的大小和细胞核数量。游动孢子比以前的报告中更大（约9.6至14.4μm），并且全部为单核。单独用次级游动孢子接种会产生初级和次级感染，即使是无毒型致病型也是如此。用无毒初级游动孢子接种未出现症状，但用无毒次级游动孢子接种会产生微小的、珠状的菌瘿。单独用致病型次级游动孢子接种导致的病害严重程度低于单独用致病型休眠孢子接种。结果表明，宿主对感染的识别以及反应的启动（抗性的诱导或抑制）在初级感染期间发生，尽管识别也可能在皮层感染和发育期间发生。
