Botrytis cinerea is the most harmful postharvest disease of table grapes. Among the
strategies that can be envisaged for its control, the use of coatings based on natural products is
particularly promising. The study presented herein focuses on the assessment of the antagonistic
capacity of two Streptomyces species and their culture filtrates against B. cinerea. Firstly, the
secondary metabolites were characterized by gas chromatography–mass spectrometry, with N1-(4-
hydroxybutyl)-N3-methylguanidine acetate and 2R,3S-9-[1,3,4-trihydroxy-2-butoxymethyl]guanine
acetate as the main compounds produced by S. lavendofoliae DSM 40217; and cyclo(leucyloprolyl)
and cyclo(phenylalanylprolyl) as the most abundant chemical species for S. rochei DSM 41729. Subsequently,
the capacity of S. lavendofoliae DSM 40217 and S. rochei DSM 41729 to inhibit the growth of
the pathogen was tested in dual culture plate assays, finding 85–90% inhibition. In agar dilution tests,
their culture filtrates resulted in effective concentration values (EC90) in the 246–3013 g mL�����1 range.
Upon the formation of conjugate complexes with chitosan oligomers (COS) to improve solubility
and bioavailability, a synergistic behavior was observed, resulting in lower EC90 values, ranging
from 201 to 953 microgramos/mL. Ex situ tests carried out on ‘Timpson’ and ‘Red Globe’ table grapes using the conjugate complexes as coatings were found to maintain the turgor of the grapes and delay
the appearance of the pathogen by 10-15 days at concentrations in the 750-1000 microgramos/mL range.
Hence, the conjugate complexes of COS and the selected Streptomyces spp. culture filtrates may be
put forward as promising protection treatments for the sustainable control of gray mold.
