Jean Swings

Bacterial diseases of rice. II. Characterization of pathogenic bacteria associated with sheath rot complex and grain discoloration of rice in the Philippines

From over 5,600 bacteria isolated from rice plants with sheath rot complex and grain discoloration syndrome, and two batches of 1 kg of rice seed (cultivars IR54 and IR8866), 204 pathogens were initially characterized by phenotypic tests, serology, and growth on selective media, and further distinguished by API 20NE, Biolog, and cellular fatty acid methyl esterfingerprints. The best differentiation was obtained by the Biolog system. The nonfluorescent pathogens were represented by clusters D1 (Burkholderia glumae, formerly Pseudomonas glumae) and E (Acidovorax avenae subsp. avenae, formerly Pseudomonas avenae). Seven clusters were distinguished among the fluorescent strains associated with sheath rot complex and grain discoloration. Cluster A5 was identified as Pseudomonas aeruginosa, and cluster B1 as P. fuscovaginae. Cluster B2 is related to Pseudomonas aureofaciens, P. corrugata, P. fluorescens, and P. marginalis. Clusters B1 and B2 were only slightly different. The strains identified as P. fuscovaginae were different from the type strains in 2-ketogluconate production.

The bacterial microflora of witloof chicory (Cichorium intybus L. var.foliosum Hegi) leaves.

The bacterial flora on the heads of four different witloof chicory varieties was examined. The 590 isolates were characterized by their SDS-PAGE protein profiles; they revealed 149 different protein fingerprint types. The fluorescentPseudomonas fingerprint type CH001 was abundantly found on all heads examined. Fourteen other fingerprint types occurred in high densities more than twice. Among these, the following were identified: fluorescentPseudomonas, nonfluorescentPseudomonas sp.,Erwinia herbicola, Erwinia sp., andFlavobacterium sp. The majority of the fingerprint types (90%) was found only once. It was also our objective to isolate bacteria applicable in the biological control of chicory phytopathogens. Isolates of all fingerprint types were tested for in vitro antagonistic activity and for possible deleterious effect on plant growth. FluorescentPseudomonas andSerratia liquefaciens isolates were antagonistic against fungi. Among the 161 fluorescentPseudomonas strains, five were able to produce disease symptoms on chicory leaves upon inoculation. Comparison of the results of this study with those obtained in two previous analyses revealed that the leaf microflora showed some similarities with the bacterial flora of chicory roots. The chicory seed microflora differed from that of both leaves and roots.

Composition of the microflora of witloof chicory seeds.

The bacterial microflora of nine varieties of witloof chicory (Cichorium intybus L. var.foliosum Hegi) seeds was studied. The 184 isolates were characterized by protein profiles determined by SDS-protein polyacrylamide gel electrophoresis of the total cell proteins. Isolates with identical protein profiles were grouped into one fingerprint type. Sixty-seven fingerprint types were distinguished. Two quantitatively major fingerprint types,Erwinia herbicola and an arthrobacter, represented 52% of the total number of isolates and were found on different chicory varieties. The latter organism was inhibited at seed germination. Other isolates, i.e.,Xanthomonas maltophilia, Pseudomonas paucimobilis, Agrobacterium radiobacter, Pseudomonas syringae, and a fluorescentPseudomonas, were only occasionally found. A minority were gram-positive isolates, i.e.,Bacillus sp.,Streptomyces sp., and coryneforms. In vitro activity of the isolates was tested against five fungi. Isolates with strong antifungal activity were found amongErwinia herbicola andBacillus sp.

The Occurrence of Phytopathogenic Pseudomonas Marginalis in a Latent Stage on the Phylloplane of Healthy Witloof Chicory ( Cichorium Intybus L. Var Foliosum Hegi.)

Six hundred and fifty bacterial strains, obtained in a survey on the phylloplane microflora of witloof chicory, were grouped by visual comparison of their protein patterns obtained by SDS-polyacrylamide gel electrophoresis. A fluorescent Pseudomonas identified as Pseudomonas marginalis may cause serious damage in witloof chicory cultivation, inducing red rot on witloof chicory leaves. We compared the protein patterns of the epiphytic fluorescent Pseudomonas isolates from healthy witloof chicory with the phytopathogenic Pseudomonas marginalis strains from culture collections. We found seven different protein pattern types within the pathogenic P. s. marginalis isolates: one of these (designated I) was also found abundantly among the protein patterns of the isolates from symptomless witloof chicory. Some of these strains, but not all, were able to cause the typical red rot symptoms on witloof chicory leaves by pricking the tissue with an infected inoculation needle. This demonstrates that the phylloplane constitutes a potential infection source of P. s. marginalis. Bruising of the witloof chicory heads during transportation may incite this pathogenic inoculum in latent phase to infection.