Variation in suppression of black-grass by modern and ancestral cereal root exudates

This study aimed to determine the variability of hexaploid wheat Triticum aestivum, ancestral diploid wheat T. monococcum, and rye Secale cereale root exudates, in their potential to inhibit the arable weed black-grass Alopecurus myosuroides, informed by precedent for variability in resistance to herbivorous pests and pathogens across this cereal germplasm. As benzoxazinoids are suggested to play a role in resistance against these stressors, and also in allelopathy, we also aimed to identify these compounds in collected root exudates. We conducted in vitro and glasshouse bioassays to determine the efficacy of a wide range of crude cereal root exudates and their constituent compounds in inhibiting black-grass in both axenic and biologically-active media. LC-MS analysis was used to characterise the constituents of these exudates and their differences between hexaploid wheat, diploid wheat and rye. Root development of black-grass was suppressed to various degrees by crude root exudates of this diverse range of cereals, with the most effective being S. cereale var. Edmondo, and T. monococcum MDR037. Benzoxazinoid content of root exudates appeared to vary, with ancestral wheat lines and rye exuding fewer of these compounds than hexaploid wheat, but with greater variability between lines. Co-culture with T. aestivum var. Gravity was significantly inhibitory to early shoot growth and biomass of black-grass seedlings, but individual benzoxazinoids had no effect on black-grass in the same system. These data provide evidence that cereal-black-grass interactions are influenced by root exudates, but that their effects cannot be replicated through the direct application of individual constituent compounds.