The Effects of Benomyl on the Growth and Development of Wheat1

Abstract

Wheat crops treated with benzimidazole‐containing fungicides have often shown small increases in yield in the absence of any detectable disease. This project was designed to test the possibility that direct physiological effects of the fungicide were responsible. The major effect of benomyl, at concentrations in the range 200–5000 ppm was to increase the development of tillers. Spraying at any one of several stages of development caused an increase in the number of tillers detected about 6 weeks later. This was found to be due to a more rapid initiation of tillers and not to more rapid growth following initiation. Associated with this earlier initiation was an increase in the incorporation of C14‐labelled assimilates into newly initiated tiller buds, but not into older ones. These responses resemble those reported for the effects of cytokinin applications to cereals. In field experiments, the increase in tiller production caused an increase in ear number only when plants were widely spaced. The decrease in tiller number as plant density increased was more rapid in treated plants than in controls, so that both treatments produced similar ear densities at around optimum plant density.