Fumonisin B1 produced in planta by Fusarium verticillioides is associated with inhibition of maize β-1,3-glucanase activity and increased aggressiveness

Abstract

Fusarium verticillioides is frequently isolated from maize worldwide as it causes seedling blight, stem- and ear rot. This ascomycete synthesizes fumonisin B1 (FB1), a mycotoxin with several targets in maize cells; it inhibits ceramide synthase, H+-ATPase, and certain isoforms of β-1,3-glucanases. FB1 production is highly variable among F. verticillioides strains thus we address whether this capacity is associated with fungal colonization, symptom induction and glucanase inhibition in maize plants. We employed four F. verticillioides strains differing in FB1 production that was verified in synthetic media and in maize embryos. We characterized one FB1-high-producing strain, a moderate-producing strain, and two low-producing strains. These strains were employed to infect maize embryos, seedlings and plants to assess fungal colonization and symptom development. High FB1production was loosely associated with higher conidia numbers in infected maize tissue, but consistently the high-FB1-producing strain caused more severe symptoms in embryos and stems than the moderate- and low-producing strains. Exo-β-1,3-glucanase activity was significantly inhibited in germinating maize embryos 24 h post-inoculation only by the FB1 high-producing strain. Our results support the role of FB1 in the infection of maize plants, and provides evidence that fumonisin produced early during the infection process might contribute to neutralize plant defenses.