Pathotype composition in Melampsora epitea populations occurring on willow (Salix) grown in mixed and monoculture plantations

Species/variety mixtures of Salix are used as a disease control strategy for rust (Melampsora epitea Thum. var epitea) in short rotation coppice (SRC). Six LET (larici-epitea typica) pathotypes and two LR (larici-retusae) pathotypes of hi. epitea var. epitea and also M. caprearum were detected ill Northern Ireland plantations in 1994 and 1995. Three of these, LET7, LET8 and NI5 were detected in plantations for the first time. The predominant pathotype on most varieties was LET1, Logistic analysis showed that this pathotype was less prevalent on Salix x dasyclados Wimm, and more prevalent on S. viminalis L. 'Bowles Hybrid: than on S. viminalis '683'. The Shannon-Weaver Index of diversity indicated that there was greater pathotype diversity in mixtures than on the constituent varieties in monoculture. There was also a general trend of increasing diversity as the season progressed. The lowest pathotype diversity was recorded on S. viminalis 'Bowles Hybrid'. Pathotype predominance and diversity have an impact on the sustainability of the crop.