The second most abundant bacterium on the root surface of young sugar beet plants was identified as a Phyllobacterium sp. ( Rhizobiaceae ) based on a comparison of the results of 39 conventional identification tests, 167 API tests, 30 antibiotic susceptibility tests, and sodium dodecyl sulfate-polyacrylamide gel electrophoretic fingerprints of total cellular proteins with type strains of Phyllobacterium myrsinacearum and Phyllobacterium rubiacearum. It was found on 198 of 1,100 investigated plants between the 2nd and 10th leaf stage on three different fields in Belgium and one field in Spain. Densities ranged from 2 × 10 4 to 2 × 10 8 CFU/g of root. Five isolates exerted a broad-spectrum in vitro antifungal activity. DNA-DNA hybridizations showed that Phyllobacterium sp. does not contain DNA sequences that are homologous with the attachment genes chvA, chvB , the transferred-DNA (T-DNA) hormone genes iaaH and ipt from Agrobacterium tumefaciens, iaaM from A. tumefaciens and Pseudomonas savastanoi , or the nitrogenase genes nifHDK from Klebsiella pneumoniae. Phyllobacterium sp. produces indolylacetic acid in in vitro cultures and induces auxinlike effects when cocultivated with callus tissue of tobacco. When Phyllobacterium sp. was transformed with a Ti plasmid derivative, it gained the capacity to induce tumors on Kalanchoe daigremontiana. The potential role of Phyllobacterium sp. in this newly recognized niche is discussed.

Fast-growing, aerobic, heterotrophic bacteria from the root surface of young sugar beet plants were inventoried. Isolation of the most abundant bacteria from the root surface of each of 1,100 plants between the second and tenth leaf stage yielded 5,600 isolates. These plants originated from different fields in Belgium and Spain. All isolates were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of total cellular proteins. Comparison of protein fingerprints allowed us to inventory the bacteria of individual plants of different fields or leaf stages and to analyze the composition and variability of the rhizobacterial population of young sugar beet plants. Each field harbored a specific population of bacteria which showed a highly hierarchic structure. A small number of bacteria occurring frequently at high densities dominated in each field. The major bacteria were identified as Pseudomonas fluorescens, Xanthomonas maltophilia, Pseudomonas paucimobilis, and Phyllobacterium sp. The former three species showed a high genetic variability as they were represented by different protein fingerprint types on the same or different fields or leaf stages. Twinspan analysis and relative abundance plots showed that the structure and composition of the bacterial populations varied strongly over time. Pseudomonads were typically early colonizers which were later replaced by X. maltophilia or Phyllobacterium sp.

Antifungal rhizobacteria were obtained from maize, barley and chicory using direct or indirect isolation procedures. Effective isolates were tested for broad‐spectrum activity against a set of phytopathogenic fungi. Isolates with broad‐spectrum activity were identified as Pseudomonas fluorescens, P. cepacia, Serratia liquefaciens, S. plymuthica and Bacillus sp. Broad‐spectrum compounds produced by P. cepacia and Erwinia herbicola were characterized as pyrrolnitrin and herbicolin‐like compounds respectively.

During the growing season of 1984, the rhizobacteria (including organisms from the rhizosphere soil, the rhizoplane, and internal root zones) of 47 maize plants (two varieties) sampled from different locations in France and at different growth stages were inventoried. Isolates were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of their total cell proteins and were found to represent 352 different protein electrotypes. Maize seedlings were initially colonized by a small number of different strains. Densities reached up to 10 8 CFU/g of root. Later in the season, the population density decreased but the heterogeneity of the rhizobacterial populations increased. Fluorescent pseudomonads represented up to 35% of the total rhizobacterial population and comprised 43 different electrotypes. Other bacteria regularly present were Xanthomonas maltophilia, Serratia liquefaciens, Pseudomonas paucimobilis, and Bacillus spp. There was a very low similarity between rhizobacterial populations of plants of the same cultivar (LG5) within one field at different growth stages and also between rhizobacterial populations of the cultivars LG5 and BRIO42 on the same field. Most electrotypes (76%) were found on a single occasion. None of the 352 electrotypes was present on all plants. In the 1985 analysis the rhizobacteria of maize seedlings (one variety) sampled from one field were characterized. They represented 236 different protein electrotypes. Thirty-three isolates showed antifungal activity against major maize pathogens; they comprised four Pseudomonas cepacia strains, producing pyrrolnitrin as well as another unknown antifungal compound.

Fifty-sixGluconobacter strains and oneAcetobacter strain were isolated from honey bees and their environment in three different regions in Belgium and identified phenotypically.