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 d eveloped 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 qua ntities, and agar concentrations. The addition of activated charcoal into t he agar medium significantly alleviated wheat allelopathic inhibition on th e root growth of ryegrass, indicating that wheat allelopathic activity is c hemically driven. There were significant differences between wheat cultivar s in their allelopathic potential at the seedling stage on the inhibition o f root elongation of annual ryegrass, varying from 23.98% to 90.91%. Re-scr eening of 22 selected wheat accessions showed that the allelopathic potenti al of wheat cultivars is consistent between different years under the same experimental conditions. This newly developed screening bioassay successful ly separated the allelopathic effect from the competitive effect between wh eat and ryegrass plants, and enabled the constant release and accumulation of allelochemicals from living wheat seedlings into the growth medium to af fect the growth of ryegrass. The influence of microorganisms was also avoid ed because of the sterile conditions. The present study describes this new bioassay suitable for the efficient screening of a large number of wheat cu ltivars under laboratory conditions.