Laboratory screening for allelopathic potential of wheat (Triticum aestivum) accessions against annual ryegrass (Lolium rigidum)

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.