Trichoderma harzianum induces systemic resistance to Alternaria alternata f. sp. lycopersici leaf necrosis in tomato

Abstract: The necrotrophic pathogen Alternaria alternata f. sp. lycopersici (AAL) causes dark-brown canker formation on stems and tissue necrosis on leaves of tomato plants. Filamentous fungi belonging to the genus Trichoderma have long been recognized as agents for the biocontrol of plant disease and promote induced systemic resistance (ISR). In this study we demonstrate the ISR effect of one isolate of T. harzianum against disease caused by AAL in plants of tomato cv. Micro-Tom. Disease symptoms were evaluated fourteen days after inoculation with T. harzianum and seven days following challenge inoculation with AAL. It was found that T. harzianum reduced approximately by 26.4% the disease symptoms in tomato plants compared to control plants not inoculated with T. harzianum. Plant genes involved in regulation of ethylene (ET) biosynthesis and response were reprogrammed by the pathogen and T. harzianum. The results obtained in this work suggest that T. harzianum is capable to increase resistance by decreasing the role of ET in susceptibility during AAL colonization of tomato leaves by attenuating ET biosynthesis and responses.