Allelopathy has been receiving world-wide attention for its potential in integrated weed management. A newly developed screening bioassay, the ‘equal-compartment-agar method’ (ECAM), was used to evaluate seedling allelopathy against annual ryegrass in a collection of 453 wheat accessions originating from 50 countries. Significant differences in allelopathic potential were found in this worldwide collection, inhibiting root growth of ryegrass from 9.7% to 90.9%. Wheat seedling allelopathy also varied significantly with accessions from different countries. Wheat allelopathic activity was normally distributed within the collection, indicating the involvement of multiple genes conferring the allelopathic trait. Of the 453 wheat accessions screened, 2 distinct groups were identified. Condor-derivatives were more allelopathic than Pavon-derivatives, with an average inhibition of root growth of ryegrass by 76% and 46%, respectively. Research was further extended to investigate the near isogenic lines derived from Hartog (Pavon-derivative) and Janz (Condor-derivative). Hartog and its backcrossed lines were less allelopathic than Janz and its backcrossed lines, inhibiting root length of ryegrass by 45% and 81%, respectively. These results strongly indicate that wheat allelopathic activity might also be controlled by major genes, depending on the particular populations. The present study demonstrates that there is a considerable genetic variation of allelopathic activity in wheat germplasm. It is possible to breed for cultivars with enhanced allelopathic activity for weed suppression.

A new screening bioassay, the ‘equal-compartment-agar-method (ECAM)’, was developed and employed to evaluate 92 wheat cultivars for their allelopathic activity on the inhibition of root growth of annual ryegrass ( L. rigidum ). Results showed that the allelopathic activity of wheat was associated with the sowing time of ryegrass seeds, the number of wheat seedlings, agar quantities, and agar concentrations. The addition of activated charcoal into the agar medium significantly alleviated wheat allelopathic inhibition on the root growth of ryegrass, indicating that wheat allelopathic activity is chemically driven. There were significant differences between wheat cultivars in their allelopathic potential at the seedling stage on the inhibition of root elongation of annual ryegrass, varying from 23.98% to 90.91%. Re-screening of 22 selected wheat accessions showed that the allelopathic potential of wheat cultivars is consistent between different years under the same experimental conditions. This newly developed screening bioassay successfully separated the allelopathic effect from the competitive effect between wheat and ryegrass plants, and enabled the constant release and accumulation of allelochemicals from living wheat seedlings into the growth medium to affect the growth of ryegrass. The influence of microorganisms was also avoided because of the sterile conditions. The present study describes this new bioassay suitable for the efficient screening of a large number of wheat cultivars under laboratory conditions.