title: Biocontrol of Monilinia laxa by Aureobasidium pullulans strains: Insights on competition for nutrients and space.
abstract: Two Aureobasidium pullulans strains (L1 and L8), able to prevent postharvest fruit decay, were evaluated in order to elucidate how the competition for nutrients and space was involved in their activity against Monilinia laxa, the causal agent of peach brown rot. The competition for nutrients was studied by co-culturing pathogen conidia and antagonists in different conditions of nutrient availability and avoiding contact between them. Both antagonists prevented the germination of conidia of M. laxa in water, reducing germination rate by >35%. However, L1 and L8 showed the lowest inhibition of conidial germination in peach juice at 5%, with a reduction of 12.6% and 13.9% respectively. HPLC amino acid analysis of peach juice revealed that the addition of the yeast suspension greatly modified their composition: asparagine was completely depleted soon after 12h of incubation and was probably hydrolyzed to aspartic acid by the yeasts, as aspartic acid content markedly increased. Pure asparagine and aspartic acid were tested by in vitro trials at the concentrations found in peach juice: both influenced M. laxa growth, but in opposite ways. Asparagine stimulated pathogen growth; conversely, amended medium with aspartic acid significantly inhibited the conidia germination and mycelial development of M. laxa. Scanning Electron Microscopy revealed that both strains showed a great capability to compete with M. laxa for space (starting 8h after treatment), colonizing the wound surface and inhibiting pathogen growth. This study clearly showed that A. pullulans L1 and L8 strains could compete with M. laxa for nutrients and space; this mode of action may play an important role in the antagonistic activity, especially in the first hours of tritrophic host-pathogen-antagonist interaction, although several other mechanisms can interact each other.
authors.affiliation: CRIOF, Department of Agricultural Science, University of Bologna, Via Gandolfi, 19, 40057 Cadriano, Bologna, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Di Francesco
authors.affiliation: Consiglio per la Ricerca e la Sperimentazione in Agricoltura, Centro di Ricerca per le Colture Industriali (CRA-CIN), Via di Corticella133, 40128 Bologna, Italy.
authors.forename: Luisa
authors.initials: L
authors.lastname: Ugolini
authors.affiliation: CNR ISPA, Trav. La Crucca, 3, 07100 Sassari, Italy.
authors.forename: Salvatore
authors.initials: S
authors.lastname: D'Aquino
authors.affiliation: Consiglio per la Ricerca e la Sperimentazione in Agricoltura, Centro di Ricerca per le Colture Industriali (CRA-CIN), Via di Corticella133, 40128 Bologna, Italy.
authors.forename: Eleonora
authors.initials: E
authors.lastname: Pagnotta
authors.affiliation: CRIOF, Department of Agricultural Science, University of Bologna, Via Gandolfi, 19, 40057 Cadriano, Bologna, Italy. Electronic address: marta.mari@unibo.it.
authors.forename: Marta
authors.initials: M
authors.lastname: Mari
mesh_terms: D000898:Antibiosis / Q000502:physiology*; D001203:Ascomycota / Q000502:physiology*; D001216:Asparagine / Q000378:metabolism*; D001224:Aspartic Acid / Q000096:biosynthesis*; D005638:Fruit / Q000382:microbiology*; D000067030:Fruit and Vegetable Juices / Q000382:microbiology*; D018525:Germination / Q000502:physiology; D005936:Glucans; D025282:Mycelium / Q000254:growth & development; D010935:Plant Diseases / Q000382:microbiology / Q000517:prevention & control; D000068239:Prunus persica / Q000382:microbiology*; D004718:Saccharomycetales / Q000254:growth & development*; D013172:Spores, Fungal / Q000254:growth & development
chemical_list: D005936:Glucans; D001224:Aspartic Acid; D001216:Asparagine; C009109:pullulan
keywords: Asparagine; Aspartic acid; HPLC analysis; Peach juice; SEM micrographs