Preventing spread of Fusarium wilt of Hiemalis begonias in the greenhouse

Abstract

To develop strategies to manage Fusarium wilt of Hiemalis begonias ( Begonia× Hiemalis), caused by Fusarium foetens, studies were conducted to understand how the disease might be spread in the greenhouse. Inoculum density studies showed that as few as 100 conidial ml −1 were sufficient to cause significant disease indicating that shared irrigation systems need strict sanitation along with bench tops, pots, and trays. The role of fungus gnats ( Bradysia spp.) in vectoring F. foetens within a greenhouse was studied using nylon tent cages with diseased and healthy Hiemalis begonias. Fungus gnats were released into half of the cages. In cages where fungus gnats were present only healthy plants became diseased, indicating the effectiveness of fungus gnats in spreading Fusarium wilt. The pathogen was also isolated from adult fungus gnats. In vitro studies showed that two commercially available H 2O 2-based compounds, ZeroTol ® (2.0% peroxyacetic acid and 27.0% hydrogen peroxide), and SaniDate ® (12.0% peroxyacetic acid and 18.5% hydrogen peroxide), were effective in causing 100% spore mortality at rates that would allow their use in irrigation water. Seven cultivars of Hiemalis begonias ( Begonia× Hiemalis) grown in soil infested with F. foetens were highly susceptible. No other Begonia species showed typical symptoms of chlorosis and wilt, but two cultivars of Rex begonia ( Begonia rex) exhibited significant stunting in repeated trials.