Pathotypes of Melampsora rust onSalix in short-rotation forestry plantations.

Melampsora epitea , the causal agent of leaf rust on willow (Salix spp.) in short-rotation forestry, was sampled over four consecutive years (1993–96) in Sweden. The pathotype patterns of 332 single-spore isolates were examined for virulence characteristics using a defined set of willow hosts. Thirty-seven pathotypes of M. epitea were identified and grouped into three formae speciales . No race or morph subdivision was observed among the isolates, other than the three formae speciales . For monitoring and studying the ecological and evolutionary dynamics of virulence for M. epitea , an internationally useful naming system for pathotypes is proposed, with a three-digit code referring to virulence on a specified set of standard test clones. [ABSTRACT FROM AUTHOR]