APS Homepage

Poster: Epidemiology: Systematics/Evolution


Genetic diversity of Pseudomonas syringae causing bacterial leaf spot on table beet (Beta vulgaris) and Swiss chard (Beta vulgaris subsp. cicla)
I. SAFNI (1), L. Ramos-Sepulveda (2), P. Goldman (3), M. Derie (4), L. du Toit (4), S. Koike (5), V. Stockwell (6), C. Bull (2) (1) 1Department of Agroecotechnology, Faculty of Agriculture, University of Sumatera Utara, Indonesia; (2) Department of Plant

Table beet and Swiss chard are grown throughout the US, with a significant proportion of baby leaf production in California and 90% of US seed production in Oregon and Washington. Bacterial leaf spot on beet and Swiss chard, caused by Pseudomonas syringae pv. aptata (Psa), has been reported from California and Oregon, but not yet from Washington. Since 2001, pseudomonads were isolated from surface-disinfested, symptomatic beet and chard plants grown in the western US, including Washington. Strains were variable for fluorescence on KMB agar medium, indicating populations may be diverse. Genetic diversity of the 99 strains was evaluated by repetitive extragenic palindromic PCR (rep-PCR) assay using the BOX AIR primer. Strains from a single Washington outbreak from a chard crop planted with infested seed had DNA fragment-banding patterns identical to the pathotype strain of Psa. The majority of the other isolates were identical, with a pattern similar to but distinct from the pattern of the pathotype. Three additional DNA fragment-banding patterns were observed. Strains from single outbreaks were represented in each of the alternative banding patterns. Preliminary multilocus sequence analysis and pathogenicity tests suggest a majority of bacterial leaf spot outbreaks on chard and table beet in California, Oregon, and Washington are caused by haplotypes distinct from Psa.