Leaf phenolics of three willow clones differing in resistance to Melampsora rust infection

Leaf phenolic composition in three Salix myrsinifolia Salisb, clones (V8, V 45, and V43), inoculated with Melampsora rust, was analyzed to detect local rust-induced alterations during different stages of infection (2, 7, and 2 1 days after inoculation [DAI]). Phenolic levels and percentage of uredial area varied significantly between clones, In the most resistant clone,V8, t he levels of some phenolic compounds were lower in rust-infected plants tha n in control plants at the initial stages of rust infection, suggesting a r apid response of phenolic metabolism to rust attack. Moreover, the clone V8 contained the highest constitutive (+)-catechin level, In clone V45, rust infection caused the most pronounced increase in the levels of individual p henolics at 7 DAI, This: increase may have been effective in retarding the subsequent spread and development of rust, In the most susceptible clone V4 3, rust-induced phenolic responses were less pronounced and delayed. The re sults suggest that in specific willow-rust interactions, constitutive level s of phenolics, as well as induced phenolic responses, may contribute to th e expression of rust resistance. In general, rust-induced alterations in wi llow phenolic levels are highly specific to genotype and compound and vary depending on the stage of rust development.