Beneficial effects of mycorrhizal associations on growth, and yield of cotton plants have been reported. In field soil cotton associates with arbuscular mycorrhizas (AMs) showing positive effects on production. On the other hand, efforts have been made to genetically engineer cotton with genes to confer resistance to pathogens. Antimicrobial peptides, such as magainins and cecropins, which play important roles in the defense systems of many living organisms from insects to humans, have also shown effectiveness in the control of a wide range of bacterial and fungal pathogens in plants by disrupting microbial cell membranes. In addition, transgenic hydrolytic enzymes, such as chitinase, and chitosanase, have anti-fungal potential by hydrolyzing fungal cell walls and by allowing early signal transduction inducing a rapid defensive response to pathogens attack. Despite their great potential improving disease resistance, the usefulness of the antimicrobial transgenes is limited if they also prevent mycorrhizal associations from forming in the transformed plant. To test the effect of antimicrobial genes on mycorrhizal associations, tobacco (as a model system) will be transformed to express the antimicrobial genes MSI-99, Myp30 and D4E1 under the control of the potato ubiquitin 3 promoter. The transformed plants will be inoculated with AM and the growth of the fungi will be compared with non-transgenic controls. Transgenic plants transformed with the chitosanase gene are already available and will be used to establish techniques and provide a preliminary test of mychorrizae infection. The results of this research are expected to provide valuable information about the efficiency of the AMP expression along with mychorrizal associations in tobacco roots. The ultimate step is to place antifungal transgenes into cotton provided that gene efficacy against pathogens can be demonstrated and the transgenes do not have deleterious effects on the mycorrhizal associations so important in the performance of cotton.