Does Large-Scale Cropping of Herbicide-Resistant Cultivars Increase the Incidence of Polyphagous Soil-Borne Plant Pathogens?

Abstract

Transgenic resistance to broad-spectrum herbicides is increasingly seen in various crops. With transgenic herbicie-resistant (THR) cultivars, application of broad-spectrum herbicides is no longer limited to the pre-emergence stage of the crop. Post-emergence application of these herbicides may be more effective in obtaining sufficient weed control compared with currently used herbicides, and herbicide treatment can be delayed compared with that in non-THR crops, thereby controlling weeds at a larger plant size. A well known side effect of glyphosate and glufosinate ammonium is the emergence of so-called ‘herbicide-synergists’, ie opportunistic root pathogens that accelerate the killing of roots that are herbicide-sensitive. These opportunistic plant pathogens, multiplying in the dying roots of weeds, may affect THR crops. In addition, suppressive effects of glyphosate and/or glufosinate ammonium on the saprophytic and antagonistic microflora have been reported and may enhance the activity of root pathogens. The authors hypothesize that delaying herbicide use in THR cultivars to optimize weed control results in increased infections by root pathogens. Controlled field experiments on the interactions between crops, pathogens and weeds are required to test this hypothesis.