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 fo r rust (Melampsora epitea Thum. var epitea) in short rotation coppice (SRC) . Six LET (larici-epitea typica) pathotypes and two LR (larici-retusae) pat hotypes of hi. epitea var. epitea and also M. caprearum were detected ill N orthern Ireland plantations in 1994 and 1995. Three of these, LET7, LET8 an d NI5 were detected in plantations for the first time. The predominant path otype on most varieties was LET1, Logistic analysis showed that this pathot ype was less prevalent on Salix x dasyclados Wimm, and more prevalent on S. viminalis L. 'Bowles Hybrid: than on S. viminalis '683'. The Shannon-Weave r Index of diversity indicated that there was greater pathotype diversity i n mixtures than on the constituent varieties in monoculture. There was also a general trend of increasing diversity as the season progressed. The lowe st pathotype diversity was recorded on S. viminalis 'Bowles Hybrid'. Pathot ype predominance and diversity have an impact on the sustainability of the crop.