NITROGEN-INDUCED REDUCTION IN LEAF PHENOLIC LEVEL IS NOT ACCOMPANIED BY INCREASED RUST FREQUENCY IN A COMPATIBLE WILLOW (SALIX MYRSINIFOLIA)-MELAMPSORA RUST INTERACTION
J. Hakulinen, 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, 102(1), 1998, pp. 101-110
Phenolic compounds are potential antimicrobial agents in willows (Sali
x 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 ava
ilability). In the present study, the combined effects of nitrogen fer
tilization and infection by pathogenic rust (Melampsora sp.) on phenol
ics and growth in willow (Salix myrsinifolia) clones were investigated
. Cutting-propagated plants of eight willow clones were subjected to l
ow and optimum levels of nitrogen Fertilization and inoculated with ru
st urediniospores or mock-inoculated with water. The plants were harve
sted 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 phenoli
c content, rust frequency and phytomass production. Plants under optim
um nitrogen availability showed increased shoot phytomass production a
nd reduced root production. Rust infection increased the root phytomas
s of willow under both fertilization treatments, but had no consistent
effect on the shoot growth of the clones. Low nitrogen availability i
ncreased the phenolic levels in willow leaves, but the rust frequency
did not differ significantly between plants grown at low and optimum l
evels of nitrogen fertilization. In several clones, rust infection inc
reased the concentrations of individual phenolic compounds, but there
were no significant correlations between phenolic concentrations and t
he level of rust infection. The results indicate that resistance in co
mpatible willow-rust interactions may not be directly governed by phen
olic compounds.