Molecular typing and spread of Clavibacter michiganensis subsp. michiganensis in greenhouses in Japan

Clavibacter michiganensis subsp. michiganensis (CMM) strains collected between 2005‐2008 from greenhouses in different locations in Okayama Prefecture, Japan, were fingerprinted by repetitive sequence‐based polymerase chain reaction (rep‐PCR) with ERIC and BOX primers. One hundred and eighty strains from eight different locations in Okayama were differentiated into four haplotypes (A to D) based on rep‐PCR. Regardless of the year of isolation, location or cultivar of tomato, the strains in each greenhouse and location belonged to the same haplotype, suggesting the strains originated from the previous greenhouse population. Based on Morisita’s index of dispersion ( I ), the distribution of diseased plants in the greenhouses, where disbudding and defoliation using either scissors or by hand were carried out in the same direction to promote the spread of CMM, occurred in an aggregated distribution in a quadrant along a row of plants, but the distribution of diseased plants indicated a random distribution in a quadrant along a furrow of plants (two adjoining rows of plants). These results showed that disbudding and defoliation contribute highly to the secondary spread of bacterial canker in commercial greenhouses.