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Seed Transmission of Fusarium verticillioides in Maize Plants Grown Under Three Different Temperature Regimes

Fusarium verticillioides can be seed transmitted and cause systemic infection of maize; however, the frequency of these phenomena has varied widely among and within individual studies. In order to better understand this variability, we evaluated the effect of temperature on the first step in the systemic infection process, the transmission of F. verticillioides from seed to seedling. Seed of a commercial maize hybrid were inoculated with a strain of F. verticillioides that had been transformed with a gene for green fluorescent protein (GFP). The seed were planted in a greenhouse potting mix and incubated in growth chambers. Plants were incubated at one of three temperature regimes designed to simulate average and extreme temperatures occurring in Iowa during the weeks following planting. Root, mesocotyl, and stem tissues were sampled at growth stages V2 and V6, surface disinfested, and cultured on a semiselective medium. At V2, >90% of root and mesocotyl tissues was infected by the GFP-expressing strain at all three temperature regimes. Also at V2, infection was detected in 68 to 75% of stems. At V6, infection of root and mesocotyl tissues persisted and was detected in 97 to 100% of plants at all three temperature regimes. Plants also had symptomless systemic infection of belowground and aboveground internodes at V6. Infection of the three basal aboveground internodes was 24, 6, and 3% for the low-temperature regime; 35, 9, and 0% for the average-temperature regime; and 46, 24, and 9% for the high-temperature regime. Seed transmission and systemic infection occurred at all temperatures and did not differ significantly among treatments. These results indicate that, if maize seed is infected with F. verticillioides, seed transmission is common and symptomless systemic infection can be initiated under a broad range of temperature conditions.