Interactions between leafcutting ants, endophytic fungi and plants

• Ano de defesa: 2011
• Autor(a) principal: Rocha, Silma Leite
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Formiga-cortadeira; Atta laevigata; Micologia; Pragas - Controle biológico; Manejo integrado de pragas; Entomologia agrícola; Ecologia
• Link de acesso: https://locus.ufv.br//handle/123456789/26680

The aim of this research was to study the interaction between two pairs of mutualistic and symbiotic organisms: forest plants (in this case Atlantic forest) and endophytic fungi on the one hand, and leafcutter ants and their fungal symbiont on the other. In this context, the first part of this thesis is a review and synthesis of interactions (known or predicted) between the plant-endophyte mutualism and the ant-fungus mutualism. In the second part, we verified the presence of endophytic fungi in vegetative fragments that were being carried and were in middens of Atta laevigata in five fortnightly collections. A high fungal diversity was found and some fungal genera were found more or less than expected in rejected midden material. The genera Glomerella, Mycelia sterilia sp. 22, Pestalotiopsis, Phomopsis sp. 1 and Xylaria were more prevalent in carried fragments while the genera Cylindrocladium, Drechslera, Epicoccum, Fusarium, Mycelia sterilia sp. 21, Trichoderma e Ulocladium and Ulocladium were found more in rejected fragments from middens. A new finding was the genera Ulocladium and Trichoderma as endophytes in leaves of tropical plants. We discuss the potential risks of these endophytes, in particular the mycoparasites Trichoderma and Epicoccum. In the third part, ten nocturnal collections were made according to the same scheme but with the ant Atta sexdens rubropilosa. In this instance, Trichoderma was found to be more prevalent in rejected midden material than expected, possible indicating active rejection of these fragments. The Trichoderma isolates found were paired off in in vitro experiments against the ants’ mutualist fungus Leucoagaricus gongylophorus. We found that L. gongylophorus inhibited the growth of all of the Trichoderma isolates, indicating a potentially important line of defence for the colonies. We also investigated the endophytism of ten of these Trichoderma isolates in the plants Ligustrum japonicum and Eucalyptus grandis. Generally, endophytism was weak in L. japonicum although an important observation was made of the presence of some isolates in the bud. This was not found in E. grandis but in this plant endophytism was more expressive. Importantly, some isolates were re-isoltaed from leaves above the inoculated area, indicating the potential for systemic infection of plants. In the final part of the thesis, an isolate of Trichoderma supposed mycoparasite was offered with rice to queenless mini-colonies of the A. sexdens rubropilosa. No effects were found of the presence of this fungus on foraging activity, the amount of rice or leaves harvested or the amount of waste produced. Although no effect was found on survival time of the colonies, there were few of these. There was however a reduction in the survival time of the workers from Trichoderma-infected. To conclude, perspectives are offered for future study of this system, focussing in particular on the potential use of Trichoderma in biological control of leafcutter ants.