Abstract
Pathogenicity was determined in four stocked bacterial strains, isolated from Suminori-diseased laver thalli of Porphyra spp. in 1985, 2002, 2003, and 2004 when the Suminori disease occurred in the Ariake Sea. Even though all isolates caused the same symptoms of Suminori disease on infected laver thalli of P. yezoensis, they belonged to completely different families. Among them, in 1985 an isolate was identified as being closely related to Arthrobacter tumbae, whereas the other three recent isolates were related to Gaetbulibacter saemankumensis. The quantitative detection of the pathogen also revealed that the isolate of G. saemankumensis, and not A. tumbae, was commonly found on normal cultivated laver thalli. Furthermore, it was observed that the sensitivity to bacterial infection corresponded to the deterioration in the physiological condition of the laver thalli. The results obtained in this study strongly suggest that a variety of factors influence the incidence of Suminori disease.
