Evaluation of the resistance induction in zucchini caused by foliar application of a Cyanobacterium extract

Cyanobacteria are components of fertilizer compounds which may interfere with plant physiology, making plants less susceptible to biotic and abiotic stresses. The aim of this research was to study the possibility to induce systemic resistance in zucchini plants by foliar application of an extract of the cyanobacterium BEA 0300B strain belonging to Nostocaceae family. Two trials were carried out under controlled conditions: the first one consisted in a biological assay of BEA 0300B extract against Podosphaera xanthii and the second one in biochemical assays to test the involvement of induced resistance. Chitosan was used as positive control, since it is a well-known resistance inducer. BEA 0300B extract (2 g L-1) was applied by spraying one of the two cotyledon leaves in both experiments, while the pathogen was inoculated on the non-treated leaves (in the biological assay only). Disease symptoms were recorded as percentage of infected area on non-treated leaves 7-9 d after pathogen inoculation. For the biochemical assays, total proteins were extracted following a non-denaturing method and the expression of some PR-proteins (PR-3, PR-5 and PR-9) was tested by spectrophotometric methods. The biological assay revealed that the BEA 0300B extract reduced the disease by 20%, similarly to chitosan, with respect to the inoculated control. Enzymatic analysis showed differences of the enzymatic activities between treated and non-treated plants, suggesting the ability of the extract tested to induce some systemic resistance in zucchini.