Effect of trichodiene synthase encoding gene expression in Trichoderma strains on their effectiveness in the control of Acanthoscelides obtectus

Abstract

Acanthoscelides obtectus, known as the bean weevil, is an insect pest that feeds on wild and cultivated common beans. Four Trichoderma isolates, two trichodiene (TD) producers (T34–5.27, E20–5.7) and their corresponding parental strains (T34, E20), were evaluated to determine the effect of their metabolites against A. obtectus adults. TD is a non-phytotoxic Volatile Organic Compound (VOC), which is the first commitment intermediate in the biosynthesis of trichothecenes. Accumulated emergence of insects was reduced in beans treated with these fungal isolates, being more reduced with E20 and T34 strains. TD producer strains, which previously showed to produce a higher number of damaged beans than their respective parental strains, gave rise to a higher insects emergence. Beans treated with fungal isolates had a lower weight loss than the control treatment, with T34 exhibiting the lowest weight loss among all fungal isolates analyzed. Furthermore, E20 showed the higher repellent activity against A. obtectus adults and produced a smaller number of holes per bean. Thus, Trichoderma isolates evaluated are good for the biological control of A. obtectus pest on beans, in which the parental strains (E20 and T34) were those exhibiting a better control of this insect than their respective TD-producer derivates strains. These results suggest that production of TD reduces effectiveness of Trichoderma T34 and E20 strains to control this insect pest.