Soil Microorganisms

The application of organic materials (powdery chitin, crab shell or rice bran) to soil enabled to suppress clubroot disease caused by Plasmodiophora brassicae. The disease severity was reduced when 1.5-2.5% (w/w) of powdery chitin was applied at 1 week before sowing, 1.5-2.5% of crab shell at 1 or 2 weeks before sowing, or 0.5-1.0% of rice bran at 2 weeks before sowing. However, the disease-suppressive effect of these organic materials decreased when the inoculum density in soil increased. When these organic materials were applied before sowing, the population of resting spores decreased more than in the nonamended soil. Factors such as pH, content of exchangeable calcium and number of actinomycetes in soil were assumed to influence the suppression of clubroot disease.

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LysM domains of the NFR1 and NFR5 receptors mediate the perception of the rhizobial Nod factor signal in Lotus japonicus. LysM domains of NFR receptors in soybean were also isolated from cv. Williams 82 as orthologs of LjNFR1 and LjNFR5. However, the genetic diversity of the LysM domains in Glycine max and Glycine soja in Japan and the role of their LysM domains in competitive nodulation between B. japonicum and B. elkanii have not yet been elucidated. A total of 39 cDNAs corresponding to the LysM domains of NFR5a were isolated from wild and cultivated soybeans using the PCR method. A phylogenetic tree based on differences in the nucleotide sequences was constructed by the NJ method and the 39 LysM sequences were classified into 3 singletons and a major cluster. The LysM sequences of 13 wild soybeans and those of all the cultivated soybeans were grouped together into the major cluster. Based on the deduced amino acid sequences, 14 of the 39 LysM domains were identical to that of cv. Enrei. Prunetin, an isoflavonid, induced the nod gene expression of B. japonicum at concentrations ranging from 5 μM to 20 μM, but not that of B. elkanii. A competitive root nodulation test using B. japonicum and B. elkanii on cv. Enrei was carried out under differential nod gene expression treatment using prunetin. Without prunetin, the root nodule number of B. japonicum on cv. Enrei was similar to that of B. elkanii. However, with prunetin, the root nodule number of B. japonicum was significantly higher than that of B. elkanii. These findings indicate that there may be a positive relationship to the root nodule number between the amount of Nod factors produced by B. japonicum and B. elkanii and Nod factor perception of the LysM domain corresponding to cv. Enrei.

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