Allelopathic interference of Ambrosia trifida with wheat (Triticum aestivum)

Ambrosia trifida is worldwide spreading in ecological terms as pioneer species and is one of the most economically destructive weeds occurring on arable lands in North China. It has long been suspected of using allelopathy to interfere with the growth and establishment of crop plants, but the mechanisms involved in allelopathy is largely unknown. In this study, a series of experiments were conducted to assess the phytotoxicity and to identify the allelochemicals of A. trifida against wheat (Triticum aestivum). The results showed that wheat growth could be significantly inhibited in A. trifida infested or residue amended soils in Northeast China. Two carotane-type sesquiterpenes, 1α-angeloyloxy-carotol and 1α-(2-methylbutyroyloxy)-carotol, were subsequently isolated and identified from the toxic soils. Both compounds had high inhibitory activity on wheat growth. Their inhibition thresholds were 11.5 μg/g soil for 1α-angeloyloxycarotol) and 16.3 μg/g soil for1α-(2-methylbutyroyloxy)-carotol. Furthermore, these two compounds were detected from A. trifida infested and residue amended soils. Their amounts ranged from 13.7 to 43.2 μg/g soil. As a result, A. trifida could release sufficient quantities of 1α-angeloyloxycarotol and 1α-(2-methylbutyloyloxy)-carotol into the soil to act as allelochemicals inhibiting the growth of wheat. The study suggested that 1α-angeloyloxy-carotol and 1α-(2-methylbutyroyloxy)-carotol could be key allelochemicals in A. trifida infested wheat fields and that A. trifida interferes with wheat growth via allelopathy.