VIEW ARTICLE

Ecology and Epidemiology

Characterization of Epiphytic Xanthomonas campestris pv. phaseoli and Pectolytic Xanthomonads Recovered from Symptomless Weeds in the Dominican Republic. Rosendo Angeles- Ramos, Department of Plant Protection, S.E.A., C.E.S.D.A., San Cristobal, Dominican Republic; Anne K. Vidaver(2), and Paula Flynn(3). (2)Department of Plant Pathology, University of Nebraska, Lincoln 68583-0722; (3)Department of Plant Pathology, Iowa State University, Ames 50011. Phytopathology 81:677-681. Accepted for publication 1 February 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-677.

Xanthomonas campestris pv. phaseoli and pectolytic xanthomonads were isolated from symptomless weeds collected inside and adjacent to fields of dry edible beans (Phaseolus vulgaris) showing common blight symptoms in the Dominican Republic. Strains of X. c. phaseoli were identified on the basis of characteristic yellow colony pigmentation; starch hydrolysis on the semi-selective medium MXP; pathogenicity on dry bean leaves and pods; absence of extracellular melanin ‘fuscans’ pigment on modified nutrient broth yeast extract and King’s medium B; and isolation of xanthomonadin pigment with a characteristic R_f value of 0.45 determined by thin-layer chromatography. Pectolytic xanthomonads also had most of the aforementioned properties, except that they failed to induce disease on bean leaves, caused an atypical incompatible response on bean pods, showed strong pectolytic activity on crystal violet pectate medium, and grew at 4 C on yeast extract-dextrose-calcium carbonate medium. Single-dimension polypeptide analysis of cellular proteins by polyacrylamide gel electrophoresis showed that the two groups of bacteria were distinctly different in their overall profiles. The percentage of pathogenic strains from 77 weed samples was 22% of the 132 strains collected. The majority of the pathogenic strains (91%) were recovered from inside infected bean fields. These results suggest that weeds may not be an important inoculum source for the common blight bacterium, but that they could serve as a reservoir of inoculum and harbor atypical xanthomonads of unknown function as well.