In vitro culture of Leucoagaricus gongylophorus (Agaricaceae), symbiont fungus of the leaf-cutting ant Atta mexicana (Hymenoptera, Formicidae), using solid and plant-supplemented culture media

Background and Aims: The mutualism between leaf-cutting ants and the fungus Leucoagaricus gongylophorus is a remarkable instance of insect-fungus symbiosis. In this study, we aimed to make a molecular identification of the L. gongylophorus strain obtained from the fungal garden of Atta mexicana, to compare the mycelial growth of the strain in several culture media and PDA medium enriched with foliar material from several plants and perform a cost analysis for the in vitro maintenance of the symbiont fungus.Methods: Seven solid culture media were compared for the in vitro growth of Leucoagaricus gongylophorus isolated from an Atta mexicana nest. In addition, we compared the fungal growth on Potato Dextrose Agar (PDA) medium enriched with selected foliar material from the leaves of six plants previously known to be either well-foraged or avoided by Atta mexicana.Key results: Higher mycelial growth percentages were obtained on compost extract added with a mineral mixture (CE) (27.3±12.7 mm) and PDA media (25.3±1.15 mm) at 28 days of growth. Furthermore, this is the first study reporting the growth of a fungal symbiont of Atta mexicana on CE, complete basic medium (CBM), Pagnocca A, and B media. PDA media enriched with some plants did not show advantages for fungus growth. Lower mycelial growth percentages were obtained on PDA media enriched with Rosa alba (0.0±0.0 mm), Coffea arabica (5.3±0.66 mm), Citrus reticulata (3.0±1.0 mm), and Psidium guajava (2.0±1.15 mm) leaves, in comparison with the control treatment (PDA medium).Conclusions: The use of culture media like CE and CBM might be a cost-effective alternative for in vitro culture of Leucoagaricus gongylophorus, even in the absence of ants. Leaves of some plant species inhibit in vitro growth of this fungus, in line with their status as plants avoided by Atta mexicana. The strong inhibition of the extract of Rosa alba, the best-foraged plant by Atta mexicana, suggests the existence of particularly effective detoxification mechanisms in natural conditions.