Suppression of clubroot disease under neutral pH caused by inhibition of spore germination of Plasmodiophora brassicae in the rhizosphere
Suppression of clubroot disease under neutral pH caused by inhibition of spore germination of Plasmodiophora brassicae in the rhizosphere
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DOI：
10.1111/j.1365-3059.2007.01817.x
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发表时间：
2008-06
期刊：
影响因子：
2.7
通讯作者：
Reiko Niwa;Yoshinobu Nomura;M. Osaki;T. Ezawa
中科院分区：
文献类型：
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作者：
Reiko Niwa;Yoshinobu Nomura;M. Osaki;T. Ezawa
为了阐明在中性土壤pH下根肿病抑制的机制，基于以下假设设计了在土壤培养条件下的高度可重复的萌发测定系统：萌发的芸苔根肿菌孢子可以通过核的缺失（即，已经释放游动孢子以感染宿主植物的根毛）来鉴定。芜菁用芸苔黑腐病菌的孢子悬浮液以2·0 × 106孢子g-1土壤的比率接种Perviridis幼苗，并在生长室中生长7天。从根际和非根际土壤中回收孢子，并用荧光增白剂28（细胞壁特异性）和SYTO 82橙子荧光核酸染色剂（核特异性染色剂）染色。在UV激发下计数孢子总数，并计数在G激发下具有发橙子荧光的核的孢子。培养7天后根际无核孢子（萌发孢子）百分比的显著增加以及与根毛感染的相关性验证了测定系统。应用富含钙的堆肥或碳酸钙来中和土壤显着降低了根际萌发孢子的百分比，以及根毛感染的数量。本研究提供了直接的证据，孢子萌发的抑制是在中性土壤pH下抑制病害的主要原因。
To elucidate the mechanism of clubroot suppression under neutral soil pH, a highly reproducible germination assay system under soil culture conditions was designed based on the hypothesis that germinated spores of Plasmodiophora brassicae could be identified by the absence of a nucleus (i.e. having released a zoospore to infect a root hair of the host plant). Brassica rapa var. perviridis seedlings were inoculated with a spore suspension of P. brassicae at a rate of 2·0 × 106 spores g−1 soil and grown in a growth chamber for 7 days. The spores were recovered from rhizosphere and non-rhizosphere soils and stained with both Fluorescent Brightener 28 (cell-wall-specific) and SYTO 82 orange fluorescent nucleic-acid stain (nucleus-specific stain). Total numbers of spores were counted under UV-excitation, and spores with a nucleus that fluoresced orange under G-excitation were counted. The significant increase in the percentage of spores without a nucleus (germinated spores) in the rhizosphere after 7 days’ cultivation and the correlation with root-hair infections validated the assay system. Applications of calcium-rich compost or calcium carbonate to neutralize the soil significantly reduced the percentage of germinated spores in the rhizosphere, as well as the number of root-hair infections. The present study provides direct evidence that the inhibition of spore germination is the primary cause of disease suppression under neutral soil pH.