Population structure of poplar rust Melampsora larici-populina in the UK inferred from AFLP

AFLP profiles were generated from poplar leaf rust (Melampsora larici-populina) collected from Populus trichocarpa cv. Trichobel at six sites in the UK in 2001. Of a total of 145 isolates, 121 were unique AFLP phenotypes. On one occasion, the same AFLP phenotype was found at two sites. The analysis indicated that 81.88% of the total variation was attributable to differences among individuals within replicate plots, 3.47% to differences among plots within sites and 14.65% to differences among sites. Weir & Cockerham's theta was calculated as 0.138 and theta(B), the Bayesian analogue of F-ST, as 0.146. Overall, there was sufficient gene flow among different sites to prevent genetic drift, as Nm was calculated as 1.562 using theta and as 1.462 using theta(B). Nei's genetic distance and population-assignment test indicated that the rust from a site in north-east England was differentiated from those from other sites. There was no significant correlation between genetic and geographical distances. The results indicate that sexual reproduction has a major influence on the relative lack of population structure of M. larici-populina in the UK.