| Budget Amount *help |
¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 2003: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2002: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2001: ¥2,500,000 (Direct Cost: ¥2,500,000)
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| Research Abstract |
In this study, "Mild Pathogenic Bacteria" isolated from various plants including onions, turf grasses and strawberries were identified as Burkholderia cepacia, Pseudomonas fuscovaginae and Herbaspirillum sp., respectively. B. cepacia strains were divided into two groups, i.e. genomovar (gv.) I and III. Most of gv. I strains did not have hrp genes whereas gv. III strains did, despite of negative HR induction on tobacco by all the strains. Their genetic backgrounds were diverse and did not correspond to pathogenicity. Only the presence of pectate lyase gene corresponded to maceration activity of the bacteria on onion slice.
P. fuscovaginae strains also were shown to lack the hrp genes, though they showed HR-like reaction on tobacco plants. This reaction was considered to be caused by novel pectate lyase strongly induced in planta and possibly by flagella. These observation suggested that the hrp gene is not the sole key-point genetic factor for the pathogenicity of Mild Pathogenic Bacterium. This new idea contradicts the well-established concepts for virulence of typical plant pathogenic bacteria.
In case for Herbaspirillum strains, hrp genes could be detected despite that some strains were HR-negative. Genetic library was constructed and a cosmid clone containing hrp gene was successfully screened. From the sequences of the clone, hrcV and hrcN genes were identified, which resembled to those of other β-Proteobacteria but could be allocated to a new isolated position in the course of evolution. Therefore, this group of bacteria could be positioned as a new group in plant pathogen.
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