Germination inhibitors in bracts surrounding the grain of Triticum tauschii

Pre-harvest sprouting of bread wheat is a cause of considerable economic losses for the Australian wheat industry. In this study, we have used Triticum tauschii (Coss.) Schmahl., the donor of the D-genome to bread wheat, and identified water-soluble germination inhibitors in its bracts. Germination of non-dormant T. tauschii grains was significantly delayed by imbibition in undiluted leachate (crude extract) from the bracts, whereas any dilution of the crude extract (1/10, 1/100 or 1/1000) resulted in no inhibition. Removal of proteins larger than 10 kDa from the crude extract resulted in increased germination inhibition compared with the crude extract. When purified, free phenolic compounds present in the crude extract were found to inhibit germination, but to a lesser extent than the crude extract, possibly due to losses during purification. HPLC of the free phenolic fraction indicated the presence of more than 30 compounds. Peak fractions were collected and tested for inhibitory properties. Two fractions significantly inhibited grain germination for 3 d, with one fraction, determined to contain vanillic acid, continuing to inhibit germination after 5 d. Exogenously applied vanillic acid at a concentration of 0.2 mg mL-1 was shown to significantly inhibit germination compared with water-imbibed grains. The germination inhibitor mechanism detected in the bracts surrounding the grain of T. tauschii in this study has the potential to provide protection against pre-harvest sprouting in bread wheat.