When allies differ

: AM fungal communities shape sorghum defence–growth outcomes against charcoal rot

Abstract

Most terrestrial plant species, including most crops, form symbiotic relationships with AM fungi. These fungi are widely known for improving plant phosphorus acquisition, but they also provide protective. The results from this glasshouse experiment suggest a functional divergence between the two AM fungal communities in sorghum when challenged by M. phaseolina. Community I functioned mainly in plant defence, reducing charcoal rot severity. Lesion lengths were suppressed by more than 80% during the first week of pathogen challenge, and this protection was still evident after two weeks, when lesions remained approximately half the size of those in non-mycorrhizal plants. In contrast, Community II provided little defence benefits but enhanced growth and nutrient status, promoting early plant growth with biomass increases of over one-third relative to controls, underpinned by greater root and panicle development and enhanced phosphorus uptake. However, the benefits conferred by Community II were not sustained under pathogen stress. By the second week of infection, biomass advantages were eroded, and no significant differences in plant growth were observed between the two fungal communities. These findings indicate that while Community I provided consistent defence benefits under pathogen challenge, Community II promoted growth in pathogen-free conditions but failed to maintain this advantage when plants were exposed to disease.

Date of Thesis submission	2025
Original language	English
Awarding Institution	Western Sydney University
Supervisor	Adam Frew (Supervisor), Jeff Powell (Supervisor) & Barsha Poudel (Supervisor)