Fungal endophytes from stalks of tropical maize and grasses: Isolation, identification, and screening for antagonism against Fusarium verticillioidesin maize stalks

A bioassay to screen fungal isolates for endophytic growth and antagonism a gainst Fusarium verticillioides in maize was developed. The method was base d 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 surf ace sterilized grass and maize stalks from Costa Rice, and four soil isolat es were tested for antagonism and endophyte 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 w hen the test was repeated. Reisolations fi om 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 comp etitor that is highly adapted to live in association with maize, and that a n 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.