GENETIC DIVERSITY AND HOST RANGE IN STRAINS OF ERWINIA-CHRYSANTHEMI

Restriction fragment length polymorphism (RFLP) analysis was used to study the relationships among 52 strains of Erwinia chrysanthemi differing in such factors as original host, geographical origin, and year of isolation. The strains were distributed in 10 RFLP groups. The similarity coefficients obtained with a probe encoding pathogenicity genes of E. chrysanthemi gave similar results compared to those obtained with randomly selected probes from a cosmid library of E. chrysanthemi 3937. Comparison with other classification systems, such as biovars and pectinolytic enzyme profiles, showed that RFLP analysis was the most discriminative. However, good correlation between these methods was observed when very homogenous groups of strains were analyzed. A sample of strains from different RFLP groups was assayed for pathogenicity on different plant species. Some host plants, such as potato, tomato, lettuce, and saintpaulia, were susceptible to all the tested strains of E. chrysanthemi. Others, such as dieffenbachia and philodendron, were differential hosts because they were only attacked by members of particular RFLP groups.