PHENOLIC-ACIDS IN WHEAT CULTIVARS IN RELATION TO PLANT SUITABILITY FOR AND RESPONSE TO CEREAL APHIDS

Contents of phenolic acids (PhAs) and activity of phenylalanine ammoni a-lyase (PAL) were examined in uninfested and infested plants of two w inter wheat cultivars differing in resistance to cereal aphids. The fo llowing PhAs were determined in their free forms in uninfested leaves of the partly resistant cv. 'Regina' and the susceptible cv.'Zdar': p- hydroxybenzoic, vanillic, p-coumaric and ferulic acids. The level of t otal PhAs was higher in 'Regina' and the content of p-coumaric acid, t he dominant acid in extracts, was nearly three times higher in this cu ltivar than in 'Zdar'. The same spectrum of PhAs was found in ears of both cultivars, and in addition, sinapic acid was detected in ears of 'Regina'. Infestation by Metopolophium dirhodum, Rhopalosiphum padi an d Sitobion avenae induced in leaves and ears of both cultivars an incr ease of PAL activity and changes in the contents of PhAs. In spire of the induction of PAL activity, the level of PhAs in the infested leave s decreased, mainly due to a decline of p-coumaric acid content. Three unidentified substances of phenolic character were found at relativel y high levels in infested leaves. The level of p-coumaric acid approxi mately doubled in infested ears of both cultivars, bur the levels of t he other PhAs were higher in 'Regina'. These results are discussed in relation to crop resistance against aphids.