Biotic filters in fungal endophyte community assembly

• Main Author: Saunders, Megan
• Other Authors: Kohn, Linda M.
• Language: en_ca
• Published: 2010
• Subjects: fungal endophytes; Fusarium; 0329
• Online Access: http://hdl.handle.net/1807/24871

My work focuses on the community ecology of symbioses, specifically of fungal endophytes and their hosts. This thesis describes how plant defense compounds and a seed endophyte influence community structure of maize fungal endophytes. Maize produces benzoxazinoids (BXs), compounds toxic to microbes and insects. I assessed the influence of three factors on endophyte communities: host BX production, host neighbor identity and presence of a BX-detoxifying endophyte, Fusarium verticillioides (FV). To determine the influence of BXs on communities, two BX-producing (BX+) and one BX-nonproducing (BX–) genotype were planted in Ridgetown and Harrow, Ontario (triculture). Fungi were isolated and tested for tolerance to 2-benzoxazolinone (BOA), a toxic BX byproduct. Species and functional diversity (community distribution of BOA tolerance levels) was calculated. In seedling roots and mature leaves, the community proportion with low BOA tolerance was greater in BX– than BX+ plants. Fusarium abundance was up to 35 times higher in mature leaves of BX+ than BX– plants. Next, to assess the effect of host neighbor identity on communities, BX– monocultures were planted, and communities from BX– plants in monoculture and triculture compared. Monoculture root communities had higher species diversity than those in triculture. In vitro experiments were conducted to evaluate the influence of BOA on endophyte species interactions. FV facilitated species with lower BOA tolerance in the presence of BOA. Finally, fields were planted with a BX+ and BX– genotype in Ontario, Canada and Georgia, USA. Seed was inoculated with FV (FV+) or sterilized (FV–). FV abundance was highest in BX+FV+ plants, and Fusarium abundance was greater in BX+ than BX– plants in mature leaves. In Georgia, BX+FV+ communities in below ground tissue had lower abundance of BOA sensitive species than BX+FV–. Overall, results suggest that BXs are a habitat filter that increased colonization by horizontally transmitted and seed-born Fusarium species. This invokes the hypothesis that selective breeding for enhanced BX concentrations increased abundance of Fusarium species in maize. The in vitro study indicated that FV could facilitate other species. In contrast, field results suggest that FV interacts competitively with community members, a trait enhanced in the presence of BXs.