Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2002
Publication Date: N/A
Interpretive Summary: Problem: Newly emerging foliar bacterial diseases of crucifers, specifically: broccoli, broccoli raab, and broccolini, were found in the Salinas Valley of California. The relatedness of the pathogens causing these diseases was unknown. Also, the relatedness of these pathogens to the known crucifer pathogen, Pseudomonas syringae pv.maculicola was also unknown. Given the value of crucifer production in the Salinas Valley and the intensity of land usage within a season, these diseases threaten to become persistent problems in widespread areas. Findings: A new pathogen, Pseudomonas syringae pv. alisalensis, is distinct from Pseudomonas syringae pv. maculicola and causes bacterial blight of broccoli and bacterial blight of broccoli raab. The pathogen found on broccolini has been identified as the existing pathogen of crucifers, Pseudomonas syringae pv. maculicola. Additional hosts for these pathogens have been identified. Benefit: Disease management measures may now be directed towards avoiding the replanting of susceptible crucifer crops after crops that have been affected by the bacterial blight disease. Avoidance of susceptible crops can also be developed as a management strategy for broccolini leaf spot.
Technical Abstract: The etiology of three foliar bacterial diseases of crucifers and the relationships between their causal agents were evaluated. Data from LOPAT and carbon utilization tests, and fatty acid analysis indicated that bacterial blights of broccoli and broccoli raab, and leaf spot of broccolini, were caused by strains of Pseudomonas syringae. Data from phage sensitivity, ice nucleation, single carbon source utilization, BOX-PCR, and host range analyses were identical for the pathogen causing leaf spot of broccolini and P. syringae pv. maculicola. The broccoli raab and broccoli pathogens infected broccoli raab, all crucifers tested, tomato, and three monocots (California brome, oat, and common timothy). None of the other pathogens tested (P. syringae pv. maculicola, P. syringae pv. tomato, or P. syringae pv. coronafaciens) caused disease on broccoli raab or on both crucifers and monocots. Data from phage sensitivity, ice nucleation, single carbon source utilization, BOX-PCR, and host range analyses were identical for the pathogens from broccoli raab and broccoli, but were different from other pathovars tested, and supported the hypothesis that a new pathovar of P. syringae pv. alisalensis pv. nov. caused a leaf blight on broccoli and broccoli raab.