Isolation of Rhizomonas suberifaciens in Florida. L. E. Datnoff, University of Florida, Everglades Research and Education Center, Belle Glade 33430. R. T. Nagata, University of Florida, Everglades Research and Education Center, Belle Glade 33430. Plant Dis. 74:394. Accepted for publication 15 December 1989. DOI: 10.1094/PD-74-0394B.
Corky root caused by Rhizomonas suberifaciens van Bruggen,
Jochimsen, & Brown is an important disease of lettuce (Lactuca sativa
L.) grown in California (1,2). Corky root occurs in Florida and
apparently is caused by the same bacterium. When the cultivar Ithaca
was seeded into naturally infested soils, plants developed yellow-banded
areas and rough, greenish brown cracks on taproots within
30 days; plants grown in fumigated soil showed no symptoms.
Symptomatic roots of Floribibb plants collected from naturally
infested fields yielded slow-growing, gram-negative bacteria that
produced colony forms identical to those produced by a known culture
of the pathogen on S-medium (2). Strains isolated from Floribibb
and Ithaca plants plus a known strain of R. suberifaciens (1 X 108
cfu/ml) produced typical symptoms in inoculated Ithaca plants.
Bacteria reisolated in pure culture from these plants resembled R.
suberifaciens in colony morphology and fatty acid analysis. Thus,
the cause of corky root in Florida is similar to that reported by van
Bruggen et al in California (2).