Inducible production of phenolic acids in wheat and antibiotic resistance to Sitodiplosis mosellana

Larvae of the wheat midge, Sitodiplosis mosellana (Gehin) feed on the surface of wheat seeds for about 10 days beginning when pollination occurs. A few wheats have a high level of antibiotic resistance to the larvae, which suppresses their growth and development. Nearly all larvae develop successfully on susceptible wheats. Analysis by HPLC of seed extracts produced by alkaline hydrolysis revealed rapid changes in the levels of p-coumaric and ferulic acids during early seed development. Seed infested by wheat midge larvae showed induced changes in the dynamics of these phenolic acids. The most resistant wheats had a higher constitutive level and a more rapid induction of ferulic acid than susceptible wheats. Levels of ferulic acid exceeding 0.35 mu g/g fresh weight were associated with a high mortality of newly hatched larvae. In one wheat line, resistance also was associated with induced production of p-coumaric acid. The induction of ferulic acid was similar in wheat from the laboratory and field, except in one resistant wheat that produced higher levels in the field. In ripe seeds, resistant and susceptible wheats had similar levels of phenolic acids.