Biological control of root rot in lettuce caused by Exserohilum rostratum and Fusarium oxysporum via induction of the defense mechanism

Root rot diseases of plant are accountable for crop yield losses. Biological control of this disease is considered a feasible alternative and eco-friendly method. The root rot pathogens, Exserohilum rostratum HQ905473 and Fusarium oxysporum HQ905448, were isolated from lettuce plants. Biocontrol activity of Trichoderma harzianum JF419706 and Bacillus subtilis HQ656002 against lettuce root rot and their inducibility of the defense genes were evaluated. The results confirm the efficiency of T. harzianum and B. subtilis either singly or as a mixture in the control of the disease and alleviation of the negative effect of the pathogens on lettuce plants. The phytosanitary parameters of the plants, including plant height and weight, was greatly enhanced as a result of the application of bioagents. Content of photosynthetic pigments and primary metabolites (carbohydrates, proteins and proline) significantly increased in the treated plants. The Differential display PCR reaction (DD-PCR) revealed that 15 up- and down-regulated genes were detected in the treated plants. Among these genes, the encoded GTPase activating protein, that is an important gene in the plant defense mechanism, was identified. Gene expression was analyzed in inoculated plants after 25 and 50 days. The 50-day-old plants had a higher level of gene expression than the 25-day-old plants. The results confirmed the efficiency of the bioagents in enhancing the defense mechanism of plants against the disease and ensure the sustainability of this resistance throughout the life of the plant.