2024-03-29T00:19:18Zhttps://eprints.lib.hokudai.ac.jp/dspace-oai/requestoai:eprints.lib.hokudai.ac.jp:2115/381862022-11-17T02:08:08Zhdl_2115_20046hdl_2115_138Suppression of clubroot disease under neutral pH caused by inhibition of spore germination of Plasmodiophora brassicae in the rhizosphereNiwa, ReikoNomura, YoshinobuOsaki, MitsuruEzawa, TatsuhiroBrassica rapanuclear/cell-wall double stainingrhizospheresoil pHsoilborne diseasespore germination470To 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.British Society for Plant PathologyJournal Articleapplication/pdfhttp://hdl.handle.net/2115/38186https://eprints.lib.hokudai.ac.jp/dspace/bitstream/2115/38186/1/PPniwa_etal.pdf0032-0862Plant Pathology5734454522008-06enginfo:doi/10.1111/j.1365-3059.2007.01817.xThe definitive version is available at www.blackwell-synergy.comauthor