Trichoderma harzianum seed treatment combined with biofumigation by Brassica carinata meal to reduce lettuce damping off by Pythium ultimum

Abstract: Seed treatment by biological control agents, like the filamentous fungus Trichodermaspp. represents a valuable option to control those pathogens which attack seedlings, causing preandpost-emergence damping off, like Pythium spp. Another sustainable tool for the control ofsoilborne pathogens is represented by the biofumigation technique which is based on the soilamendment with Brassicaceae derived products, through the green manuring of cover crops orseed meal amending. The aim of this work was to evaluate the effect of combining the seedtreatment by Trichoderma harzianum isolate with the biofumigation by Brassica carinata meal,to control damping off of lettuce. The experiments were carried out in two types of soil,artificially inoculated by a pathogenic isolate of P. ultimum. The T. harzianum isolate waspreviously selected for tolerance to biofumigation compounds and it was applied to seeds asconidia suspension or liquid culture. In the first type of soil only liquid culture seed treatmentsignificantly increased the percentage of healthy plantlets, irrespective to biofumigation,suggesting a role for the metabolites produced during T. harzianum in vitro growth. These resultswere substantially confirmed also with the second type of soil.