Genetic structure and spatial distribution of the mycoparasite Sphaerellopsis filum on Melampsora larici-epitea in a short-rotation coppice willow planting

AFLP analysis was used td examine the genetic structure of the mycoparasite Sphaerellopsis filum on willow rust Melampsora larici-epitea using two sets of samples of a willow clone in a short-rotation coppice planting. The first set was collected from a plot (short strip) in 1998, 1999 and 2000 and the second from another plot (long strip) in 2000. In all, 228 S. filum isolates were typed, 139 AFLP loci scored and 54 AFLP genotypes identified. In the short strip, genotypes sampled in 1998 were no longer detected in subsequent years and genotype diversity fluctuated (0 center dot 25-0 center dot 68) over the years, indicating that migration had a major impact on the genotype structure. Two distinct groups (average Nei and Li's similarity coefficient between the groups = 0 center dot 047) were identified. The group B genotypes were sampled only in 2000. Within the groups, the average similarities were > 0 center dot 96. Both the index of association test and the parsimony tree length permutation test suggest that there was a significant clonality in group A while recombination cannot be ruled out in group B. Localized clusters of AFLP genotypes were detected using the software SaTScan that is based on the spatial scan statistic. Possible mechanisms involved in the spread of S. filum in willow coppice plantations are discussed.