Escovopsis microfungi as a potential biocontrol agent of Acromyrmex lundii´s cultivar: virulence and induction of the pathogen

MARFETAN, JORGE ARIEL; GOROSITO, NORMA B.; FOLGARAIT, PATRICIA J.

Villa Carlos Paz, Cordoba

Congreso; VI Congreso Argentino de Microbiología General; 2009

Sociedad Argentina de Microbiología General

Leaf-cutter ants (Acromyrmex and Atta) are the dominant herbivores of the Neotropics. In Argentina, Acromyrmex lundii is one of the most important pests of plantations, horticultural crops, and pastures. The leaves cut by the ants are used as a substrate for the cultivation of Leucoagaricus (Basidiomycotina), which represents the main food of the queen and brood. This cultivar is attacked by Escovopsis (Ascomycotina: Hypocreales), a specialist microfungi which can kill the cultivar in a short period of time, and as a consequence the colonies. We investigated the effect of one strain of the mentioned pathogen over Leucoagaricus isolated from different colonies of A. lundii from Corrientes, Argentina. Despite having a clonal propagation through ant generations, we showed -for the first time- that Leucoagaricus from different colonies exhibited different growth speed and morphology, in vitro. All cultivars, however, were negatively affected by Escovopsis reducing their growth (rate and final area), especially for the cultivar with greatest growth. On the other hand, the response of Escovopsis did not differ among cultivars in growth rate and ended up covering completely each of the cultivars within a week. However, the percentage of production of mature spores differed according to which cultivar strain was challenged with. Since we observed a greater mycelium growth rate as well as speed and amount of sporulation of Escovopsis in presence of the cultivar we hypothesized that the pathogen was induced by a soluble compound released by Leucoagaricus. We made a 3 treatments experiment; one treatment with Escovopsis growing in presence of a piece of PDA with Leucoagaricus, a second with Escovopsis growing by itself, and a third with Escovopis growing with a piece of agar coming from a plate with the cultivar. We found that Escovopsis growth and sporulation was greater in the first and third treatment in comparison to the control, demonstrating that Escovopsis was induced by a soluble compound that can diffuse in agar. These results are encouraging from the biological control perspective for three reasons. First, it is useful that Escovopsis exhibits the same performance against cultivars from different colonies assuring its negative effect at least in the same site. Second, it is desirable that the biocontrol agent asexual reproduction is induced when necessary, i.e. in presence of the organism that needs to be controlled. Finally, the inducible sporulation will probably reduce the dissemination of the biocontrol agent towards other sympatric ants after its application in the field.