Epiphytic Bacteria and Yeasts on Apple Blossoms and Their Potential as Antagonists of Erwinia amylovora

Abstract

Apple blossoms were sampled for indigenous epiphytic populations of culturable microorganisms during different stages of bloom at two locations in central Washington State and one site in Corvallis, OR. Frequencies and population sizes of bacteria on stigmas of apple were lower in Washington than at Corvallis, where average relative humidity was higher and possibly favored greater colonization; however, bacteria at Corvallis were mainly pseudomonads, whereas those in Washington were diverse, composed of several genera. In Washington, yeast as well as bacteria were isolated from both stigmatic and hypanthial surfaces. Sampled blossoms were processed immediately to assess microbial populations, or after a 24-h incubation at 28 degrees C and high relative humidity, which broadened the range of detectable taxa evaluated as potential antagonists. Identifications were based on fatty acid methyl ester profiles and rDNA sequence analyses. Yeasts or yeastlike organisms were detected at frequencies similar to or greater than bacteria, particularly in hypanthia. When microbial isolates were tested for their capacity to suppress Erwinia amylovora on stigmas of detached crab apple flowers, many were ineffective. The best antagonists were the bacteria Pantoea agglomerans and Pseudomonas spp. and a few yeasts identified as Cryptococcus spp. Further evaluation of these taxa on flowers could lead to the discovery of additional biocontrol agents for fire blight.

Efectividad in vitro de Bacillus y polifenoles de plantas nativas de México sobre Rhizoctonia-Solani

“…B. atrophaeus está reportado como agente de control sobre Erwinia amylovora con un índice de antagonismo de 0.53 (Pusey et al, 2009). Table 3 shows the species of bacteria isolated from the rhizosphere of desert plants with antagonistic effect on plant pathogen R. solani, belonging to the genus Bacillus by 16S ribosomal gene amplification.…”

“…B. atrophaeus is reported as a control agent on Erwinia amylovora with an antagonism index of 0.53 (Pusey et al, 2009).…”

Floral traits affecting fire blight infection and management

“…fluorescens (BlightBan Ò A506) and B. subtilis (Biopro Ò , Serenade Ò , Micosat F Ò ) Broggini et al 2005;Elmer et al 2005;Fravel 2005;EPA 2006a, b). Yeasts or yeastlike species being evaluated in commercial preparations include Aureobasidium pullulans, Candida sake and Metschnikowia pulcherrima (Duffy et al 2006;Jelkmann and Lindner 2008;Pusey et al 2009).…”

“…Recently, Pusey et al (2009) sampled apple flowers for indigenous epiphytic populations of culturable microorganisms during different stages of bloom, and tested the microbial isolates for their capacity to suppress E. amylovora on stigmas of detached crab apple flowers. The best bacterial antagonists were P. agglomerans and Pseudomonas spp.…”

“…Yeasts or yeast-like organisms have the advantage of a greater adaptability to high osmotic pressures, particularly on hypanthial surfaces during periods of low moisture. Further evaluation of these taxa on flowers could lead to the discovery of additional biocontrol agents for fire blight (Pusey et al 2009).…”