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Endophytic microrganisms for silverleaf disease (Chondrostereum purpureum) control in apple

Daina Grinbergs: Instituto de Investigaciones Agropecuarias

<div>Silverleaf is an important disease which produces foliar silvering, wood necrosis and reduction of fruit yield and quality. Field studies have shown spontaneous reversion of foliar symptoms, together with yield recovery. Plants are clones, thus it is postulated that resistance is driven by a non-genetic mechanism, like their microbiome. The objectives were to explore plants endophytic microbiome, to determine endophytes antagonistic activity against the pathogen, and their ability to colonize apple plants. Microorganisms were isolated from the internal trunk of diseased and reverted plants and confronted to four <em>C. purpureum</em> strains. Isolates showing the greatest antagonism were selected for further tests using their secondary metabolites and inoculating <em>in vitro</em> apple plants by drenching. Microbial diversity was greater in reverted plants (73%): 48% actinobacteria, 30% fungi and 13% bacteria. Isolates from diseased plants were not antagonistic, while 37% of the reverted ones showed activity. They were identified and morphologically, biochemically and genetically characterized. <em>Streptomyces</em> spp. isolates inhibited <em>C. purpureum</em> growth by 66 to 62%, without differences among bacterial plugs and wells containing metabolites (P<0.05%). In addition, <em>C. purpureum</em> growth was inhibited in 85-96% when metabolites were spread on the agar. Moreover, <em>Streptomyces</em> strains successfully colonized apple plants as endophytes, becoming a promising alternative for silverleaf control.</div>

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