Potential contribution of earthworms to the biological control of Fusarium graminearum in Uruguayan agroecosystems

Doctoral thesis abstract

Abstract

Fusarium graminearum is the main pathogen causing Fusarium Head Blight (FHB) in Uruguay, one of the most important cereal diseases worldwide. By surviving saprophytically in wheat straw, its survival is favored in no-till systems, which leave high percentages of plant residues on the ground. Fusarium is difficult to control, and requires an integrated management combining several control measures. In Uruguay, biological alternatives of control using Trichoderma spp. have been studied. However, there are no precedents of biological control through soil fauna, especially earthworms, which benefit plant growth and health both indirectly (through improved soil properties) and directly (by suppressing plant pathogens). Particularly, it has been shown that earthworms can reduce Fusarium biomass in the soil and in inoculated wheat straw. The present study explored the possibility of integrating the use of earthworms to control Fusarium in wheat agroecosystems in Uruguay. For this, earthworm communities in wheat systems in southern and western Uruguay were sampled. It was found that, while exotic earthworms dominated in the south, natives were dominant in the west. Among the earthworm species found, two were selected to evaluate their potential to reduce wheat straw inoculated with F. graminearum under controlled conditions. Lumbricus friendi (anecic) had a significant effect reducing soil straw cover, whereas Glossoscolex rione (endogeic) had no significant effect, probably due to their scarce activity on the surface. Finally, toxicity tests showed that two fungicides used to control FHB had an acute and chronic negative effect on earthworms, with native G. rione being more sensitive than the reference species (Eisenia fetida). It is concluded that there are earthworms in Uruguayan agroecosystems capable of contributing to the control of Fusarium, and to maximize this ecosystem service provided by the earthworms, soil managements that favor their population should be considered.