A NEW RANUNCULUS DISEASE CAUSED BY XANTHOMONAS-CAMPESTRIS

A new disease of ranunculus (Ranunculus asiaticus) was observed on sev eral cultivars in commercial fields in San Diego and Riverside Countie s, California. Symptoms included pin-point to large irregular necrotic lesions on leaves and stems and occasionally black patches along the internal margins of leaflets in association with vein chlorosis. Xanth omonas campestris was consistently isolated from diseased tissues. X. campestris was also isolated from tubers and seeds of naturally infect ed plants, which suggests a means by which the pathogen is spread in t he industry. One-year-old tubers of two cultivars (Picotee and Rose) w ere contaminated at frequencies of 4 and 7%, respectively. The frequen cy of seed contamination for 11 cultivars ranged from 1.1 to 16%. Symp toms appeared on inoculated ranunculus plants as early as 3 and as lat e as 22 days after inoculation, depending on the method of inoculation , temperature, and available moisture. Recovery of the bacterium from the tubers of plants inoculated and kept under different moisture and temperature conditions was 6.6 to 13.3%. Amplification of a DNA fragme nt specific for hrp genes by polymerase chain reaction for each strain and further analysis of the amplification product by restriction endo nuclease digestion suggested that the ranunculus strains were closely related to each other and to X. c. pv. campestris; however, pathogenic ity tests indicated that the ranunculus strains could be a different p athovar.