The arbuscular mycorrhizal symbiosis reduces disease severity in tomato plants infected by Botrytis cinerea

The majority of plants establish symbiotic associa- tions with arbuscular mycorrhizal (AM) fungi. The sym- biosis provides the plants with an improved mineral nu- trition and, to some extent, higher tolerance to biotic and abiotic stresses. In this work we have evaluated whether AM symbiosis modifies the response of tomato plants to the attack of the necrotrophic pathogen Botry- tis cinerea. Leaves of tomato plants, colonized or not by the AM fungus Glomus mosseae, were infected with B. cinerea. A higher disease index in control plants (60.3%) compared to mycorrhizal plants (37.5%) was observed. To assess the potential involvement of sali- cylic acid (SA), jasmonic acid (JA) and abscisic acid (ABA) in this response, the levels of these hormones were also measured in the leaves of mycorrhizal and non mycorrhizal plants. While JA was not detected and no differences were observed in the SA content between the two biological conditions, a statistically significant lower content of ABA was detected in mycorrhizal vs control plants. Our results show that AM symbiosis re- duces disease severity in tomato plants infected by B. cinerea and suggest that ABA is one component of the AM-induced lower susceptibility to B. cinerea.