Suceptibility to Erysiphe graminis f.sp tritici and Phenolic Acid Content of Wheat as Influenced by Different Levels of Nitrogen Fertilization

Pustule formation and conidia production of Erysiphe glʹaminis f. sp. tritici were examined on wheat plants ( Trilicum aeslifllm) supplied with different amounts of nitrate in hyd roponic cul ture. On first and fifth leaves of the cullivar Nandu inoculated with an incompatible race of powdery mildew, hypersensitive. specific resisla nce was not modified by nitrogen nutrition. On primary leaves of the compatible cultivar Syros, pustule numbers and conidia production were not a ltered by nitrogen supply. On fifth leaves of this cultivar, high nitrogen supply to the plants increased pustule numbers and sporula tion per unilleafarea, compared 10 a low disease intensity allow nitrogen level. Individual hydroxycinnamic acids (HCAs) were determined by HPLC in extracts from wheat plants cultivated at dilferent levels of nitrogen. Ferulic acid, the predominant phenolic acid as weU as p-coumaric acid were detected in primary and fifth leaves in both unbound and bound form s. In primary leaves, nitrogen supply did not modify HCA concentration. Levels of bound and unbound HCAs in fifth leaves decreased greatl y when nitrogen supply increased. Ln response to infection with a compatible race of powdery mi ldew. levels of bound and unbound HCAs sligh tly increased in leaves of the cv. Syros grown wilh low and mediulll nitrogen supply. Infection of the incompatible cv. Nandu with the same race led lO HCA acculll ulation, irrespective of nitrogen supply to the wheat plant. In primary and fifth leaves less than 5% of total alka li-sol uble unbound HCAs were lInconjugated or present in glycosides. At low nitrogen supply. bound and unbound HCAs are likely invo lved in qual11ilarive resistance of wheat to powdery mildew.