Over-expression of chitinase and ss-1,3-glucanase genes in orange fruit treated with Aureobasidium pullmans and chitosan

Chitosan and Aureobasidium pullulans, strains L47 and 547, are known for their activity in controlling a number of post-harvest diseases of fruits and vegetables. The mechanisms by which these alternative control means exert their activity are not fully elucidated, although it has been inferred that, among other mechanisms, they are able to induce resistance in the host. To confirm this hypothesis at a molecular level, the expression of two genes, known to be involved in the host resistance (chitinase and beta -1,3-glucanase), was evaluated by real-time PCR in oranges cv. Valencia late at different level of maturity (veraison and full-ripening). ATP-synthase was utilised as a housekeeping non-regulated reference gene. At the beginning of ripening the relative transcript level of chitinase was up-regulated in all treated fruits by 518- (strain L47), 726- (strain 547) and 1790-fold (chitosan). In the same fruits beta -1,3-glucanase expression was increased by L47 and 547 (55- and 20-fold, respectively) and to a minor extent by chitosan (5.4 fold). Full-ripen fruits were less reactive compared to those in the veraison stage. In particular, chitinase expression was up-regulated by 20, 83 and 259 fold in fruits treated with 547, L47 and chitosan, respectively. Very limited increases of expression were shown by the beta -1,3-glucanase gene. Our data demonstrate that L47, 547 and chitosan are able to induce resistance in orange tissues; however their action is strongly influenced by the ripening stage. Further studies are in progress to identify other genes involved in the resistance induced by strain 547 and chitosan in oranges.