Reduced growth responses of mesosulfuron-methyl-resistant blackgrass to allelopathic wheat are driven by underground chemical interaction

Aims The incidence of herbicide-resistant blackgrass is escalating in wheat fields; the development of alternatives to traditional herbicides is crucial. Allelopathic wheat can suppress blackgrass. Herein, we investigated the influence of allelopathic wheat on herbicide-resistant blackgrass. Methods Mesosulfuron-methyl-resistant and -susceptible blackgrass were used. We examined i) root interactions between allelopathic wheat and both blackgrass biotypes, ii) allelochemical 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) production by allelopathic wheat in a root segregation experiment, and iii) responses of allelopathic wheat to root exudates. Signal chemicals in the root exudates of both blackgrass biotypes were characterised. Results Allelopathic wheat inhibited the growth of roots more than shoots for resistant and susceptible blackgrass. Allelopathic wheat inhibited roots of resistant blackgrass more than those of susceptible blackgrass. Allelopathic wheat significantly shaped blackgrass root behaviour. Resistant blackgrass caused a lower relative increase in DIMBOA production by allelopathic wheat. Root segregation with 30 mu m nylon led to greater growth inhibition of blackgrass and a relative increase in allelochemical DIMBOA. Root exudates from blackgrass induced DIMBOA production, but more so for susceptible blackgrass. The concentration of (-)-loliolide, a potential signal chemical, was much lower in the root exudates from resistant than susceptible blackgrass. Conclusions Allelopathic wheat can interfere with the growth of mesosulfuron-methyl-resistant blackgrass through allelochemical-mediated root interactions. Such allelopathic interference can provide insight into weed management.