Hakulinen J
Nitrogen-induced reduction in leaf phenolic level is not accompanied by increased rust frequency in a compatible willow (Salix myrsinifolia)-Melampsora rust interaction
Physiologia Plantarum: 1998 102:101-110
Phenolic compounds are potential antimicrobial agents in willows (Salix spp.). However, little is known about their role in willow pathogen interactions. Earlier studies have shown that phenolic levels may vary depending on genotype and environmental factors (such as nutrient availability). In the present study, the combined effects of nitrogen fertilization and infection by pathogenic rust (Melampsora sp.) on phenolics and growth in willow (Salix myrsinifolia) clones were investigated. Cutting-propagated plants of eight willow clones were subjected to low and optimum levels of nitrogen Fertilization and inoculated with rust urediniospores or mock-inoculated with water. The plants were harvested 20 days after the inoculations and the dry weight of the leaves, stems and roots determined. Phenolics were analysed from leaf material using HPLC. The willow clones differed significantly in their phenolic content, rust frequency and phytomass production. Plants under optimum nitrogen availability showed increased shoot phytomass production and reduced root production. Rust infection increased the root phytomass of willow under both fertilization treatments, but had no consistent effect on the shoot growth of the clones. Low nitrogen availability increased the phenolic levels in willow leaves, but the rust frequency did not differ significantly between plants grown at low and optimum levels of nitrogen fertilization. In several clones, rust infection increased the concentrations of individual phenolic compounds, but there were no significant correlations between phenolic concentrations and the level of rust infection. The results indicate that resistance in compatible willow-rust interactions may not be directly governed by phenolic compounds.
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