title: Selection for biocontrol bacteria antagonistic toward Rosellinia necatrix by enrichment of competitive avocado root tip colonizers.
abstract: Biological control of soil-borne pathogens is frequently based on the application of antagonistic microorganisms selected solely for their ability to produce in vitro antifungal factors. The aim of this work was to select bacteria that efficiently colonize the roots of avocado plants and display antagonism towards Rosellinia necatrix, the causal agent of avocado white root rot. A high frequency of antagonistic strains (ten isolates, 24.4%) was obtained using a novel procedure based on the selection of competitive avocado root tip colonizers. Amplification and sequencing of the 16S rRNA gene, in combination with biochemical characterization, showed that eight and two of the selected isolates belonged to the genera Pseudomonas and Stenotrophomonas, respectively. Characterization of antifungal compounds produced by the antagonistic strains showed variable production of exoenzymes and HCN. Only one of these strains, Pseudomonas sp. AVO94, produced a compound that could be related to antifungal antibiotics. All of the ten selected strains showed twitching motility, a cell movement involved in competitive colonization of root tips. Production of N-acyl-homoserine lactones and indole-3-acetic acid was also reported for some of these isolates. Resistance to several bacterial antibiotics was tested, and three strains showing resistance to only one of them were selected for biocontrol assays. The three selected strains persisted in the rhizosphere of avocado plants at levels considered crucial for efficient biocontrol, 10(5)-10(6) colony forming units/g of root; two of them, Pseudomonas putida AVO102 and Pseudomonas pseudoalcaligenes AVO110, demonstrated significant protection of avocado plants against white root rot.
authors.affiliation: IFAPA, Centro de Churriana (CICE Junta de Andalucía), Cortijo de la Cruz s/n, 29140 Churriana, Málaga, Spain. clarapliego@uma.es
authors.forename: Clara
authors.initials: C
authors.lastname: Pliego
authors.forename: Francisco Manuel
authors.initials: FM
authors.lastname: Cazorla
authors.forename: María Angeles
authors.initials: MA
authors.lastname: González-Sánchez
authors.forename: Rosa María
authors.initials: RM
authors.lastname: Pérez-Jiménez
authors.forename: Antonio
authors.initials: A
authors.lastname: de Vicente
authors.forename: Cayo
authors.initials: C
authors.lastname: Ramos
mesh_terms: D015107:4-Butyrolactone / Q000031:analogs & derivatives / Q000378:metabolism; D001203:Ascomycota / Q000254:growth & development*; D001427:Bacterial Toxins / Q000378:metabolism; D006856:Hydrogen Cyanide / Q000378:metabolism; D007210:Indoleacetic Acids / Q000378:metabolism; D027421:Persea / Q000382:microbiology*; D018517:Plant Roots / Q000382:microbiology*; D011549:Pseudomonas / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D020588:Stenotrophomonas / Q000235:genetics / Q000254:growth & development / Q000378:metabolism
chemical_list: D001427:Bacterial Toxins; D007210:Indoleacetic Acids; D012336:RNA, Ribosomal, 16S; C088386:homoserine lactone; D006856:Hydrogen Cyanide; C030737:indoleacetic acid; D015107:4-Butyrolactone