INDUCED RESISTANCE IN THE BIOCONTROL OF PYTHIUM-APHANIDERMATUM BY PSEUDOMONAS SPP ON CUCUMBER

Plants of Cucumis sativus cv. Corona were grown in rockwool, with the root systems split into two separate pots. B pots were treated with water or a cell suspension of Pseudomonas corrugata isolate 13 or P. fluorescens biovar C isolate 15, two rhizosphere isolates effective as biocontrol agents against Pythium aphanidermatum. The P pot was treated with water or a suspension of zoospores of P. aphanidermatum applied at the same time (simultaneous treatment) or I week after B pot treatments. Most of the bacterial treatments reduced disease incidence and disease severity. Simultaneous treatment with isolate 15 increased shoot dry weight, leaf area, and number of fruit of inoculated plants in one trial. Some treatments with isolate 13 or 15 also increased root volume or root dry weight in B or P pots, compared to the inoculated plants where the B pot was treated with water only (Pythium control). Lower population densities of P, aphanidermatum in P pots were detected in some treatments to which bacteria were applied to the B pot, but only in the early stages of the experiment. This is the first report of systemic-induced resistance against a root pathogen in cucumber obtained by application of Pseudomonas spp. to a root system spatially separated from the pathogen-inoculated root.