PHENOLIC-ACID AND CONDENSED TANNIN CONCENTRATIONS OF 6 COTTON GENOTYPES

Phenolic acids and condensed tannins have been implicated in plant res istance to insects and diseases. The objective of this study was to de termine phenolic acid and condensed tannin concentrations in six cotto n (Gossypium hirsutum L.) genotypes that display varying degrees of sp ider mite [Tetranychus urticae (Koch)] resistance. Since phenolic acid s are precursors for condensed tannins in the shikimate pathway, the l evels of these compounds should be positively correlated. Leaf blades from whole cotton plants grown in a controlled environment were analyz ed using HPLC techniques at two growth stages (pinhead-square and firs t-bloom) for concentrations of 13 tentatively identified phenolic acid s, while condensed tannin concentrations were determined spectrophotom etrically from extracts of the topmost unfolded leaf and the fourth ma instem leaf from the terminal. Caffeic, p-coumaric and salicylic acids occurred at high concentrations relative to the other phenolic acids. Gallic, gentisic, protocatechuic, benzoic and ferulic acids occurred at intermediate concentrations; p-hydroxybenzoic, vanillic, syringic, sinapic and cinnamic acids occurred at low concentrations. Genotypes t hat exhibited higher levels of condensed tannins also had significantl y higher levels of total phenolic acids, syringic acid and p-coumaric acid concentrations. Additionally caffeic, p-hydroxybenzoic, syringic, p-coumaric and benzoic acids and total phenolic acids were highly cor related with condensed tannin concentrations. Phenolic acid concentrat ions decreased, while condensed tannin concentrations increased, from pinhead-square to first-bloom growth stages in all genotypes. While ge notypes displaying some degree of resistance to the spider mite may ha ve been selected for elevated condensed tannin levels, these genotypes also may have been inadvertently selected for high phenolic acid leve ls. Therefore, the observed resistance in these genotypes may be attri buted to high levels of not only condensed tannins, but also phenolic acids.