Fungal Endophytes from Stalks of Tropical Maize and Grasses: Isolation, Identification, and Screening for Antagonism against Fusarium verticillioides in Maize Stalks

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Abstract
A bioassay to screen fungal isolates for endophytic growth and antagonism against Fusarium verticillioides in maize was developed. The method was based on the commonly used toothpick inoculation method followed by measurement of stalk necrosis, and was designed to assure a direct introduction of the endophyte into the plant. Thirty-four fungal endophytes isolated from surface sterilized grass and maize stalks from Costa Rica, and four soil isolates, were tested for antagonism and endophytic growth. Six isolates gave less necrosis (P < 0.05) than the control treated with F. verticillioides alone, but only one isolate, Trichoderma koningii S8, reduced the stalk necrosis when the test was repeated. Reisolations from the stalk showed that none of the isolates were able to completely eliminate F. verticillioides from the maize stalk. It is concluded that F. verticillioides is a very strong competitor that is highly adapted to live in association with maize, and that an effective antagonist against F. verticillioides still remains to be found. The screening assay developed in this study may prove to be a useful tool to study the in vivo interactions between plant pathogens and antagonistic endophytes.