Disclosed are new effects of increased gdhA gene expression on plants that are susceptible to Aspergillus and Fusarium virguliforme infection. Plants transformed with the gdhA gene are resistant to aflatoxin accumulation following Aspergillus infection, and to root rot following F. virguliforme infection. The resistance to aflatoxin accumulation and root rot in gdhA+ plants is coincident with drought tolerance and resistance of the plants to certain herbicides. Methods for controlling aflatoxin contamination and root rot in crop plants, and for screening plants putatively transformed with gdhA, are described.