EndophyticFusarium verticillioides reduces disease severity caused byUstilago maydison maize

Abstract

Endophytic fungi represent diverse taxa that inhabit plant hosts without causing disease symptoms. We used endophytic isolates of Fusarium verticillioides (Sacc.) Nirenberg to understand how endophytic fungi interact with pathogens, in this case, the corn smut pathogen, Ustilago maydis DC (Corda). Endophytic F. verticillioides strains were inoculated onto maize seedlings before, simultaneously, or after inoculation with U. maydis, and the effects on smut disease severity and on plant growth were assessed. When F. verticillioides is simultaneously coinoculated with U. maydis, smut disease severity is significantly decreased and plant growth is increased, compared with other treatments. Controls show that F. verticillioides by itself does not have measurable effects on plant growth. Together, our results suggest that a commonly occurring fungal endophyte on maize, F. verticillioides, ameliorates the effects of a host-specific pathogen, U. maydis, by interfering with the early infection process and limiting disease development, resulting in increased plant growth.

Metabolome and Transcriptome of the Interaction between Ustilago maydis and Fusarium verticillioides In Vitro

“…The outcome of the interaction measured is that F. verticillioides reduces the growth of U. maydis, which may explain the reduced pathogenic potential of U. maydis previously observed (18). However, growth of F. verticillioides in the presence of U. maydis is also reduced although to a much lower extent than that of U. maydis.…”

“…Genes listed in Table S2 of reference 13 as members of expanded families in the U. maydis genome were also upregulated after 5 days in cocultivation compared to in growth alone (see Data Set S1 in the supplemental material): um01392 (family 18, questionable open reading frames [ORFs] in repetitive regions), um03558 (family 3, similarly expanded in other Basidiomycota), and um05528 (family 14, similarly expanded in Basidiomycota and Ascomycota).…”

“…Both fungi are found commonly in soil as well as in maize, and it has been shown that F. verticillioides can reduce disease severity caused by U. maydis (18). This study was intended to investigate their competition for nutrients as well as the direct antagonistic actions between the two in a controlled setting.…”

“…U. maydis U18 mating type a 2 b 11 and C7 mating type a 1 b 12 and F. verticillioides isolate NRRL 20956 were acquired from the May Lab fungal collection and the Agricultural Research Service Culture collection, respectively. The F. verticillioides isolate has been fully sequenced (20), behaves as an endophyte under greenhouse experiments (18), and has been used previously to study in vitro fungal interactions (23).…”

“…F. verticillioides, often considered solely as an ear and stalk rot pathogen of maize, is also a persistent endophytic fungus that can systemically infect maize without producing disease symptoms (2,22). F. verticillioides has been shown to reduce disease severity caused by U. maydis in maize, and so this fungusfungus interaction may be critical for understanding corn smut pathogenesis and its consequences in nature (18). Previously, we have focused on differences in metabolic profiles between the two species grown in vitro in single cultures and in cocultures in an effort to understand how accumulation of small molecules may affect this interaction (23).…”