Pathogenic variation in poplar rust Melampsora larici-populina from England

Abstract

Using a leaf disc method, 19 isolates of the poplar rust, Melampsora larici-populina , and one isolate of M.␣populnea from England were inoculated on to 25 poplar clones belonging to Populus nigra and P.␣trichocarpa, and hybrids between P. deltoides and P. nigra, P. deltoidesand P. trichocarpa, P.␣tacamahaca and P.␣trichocarpa, and P. alba and P. tremula. Disease was scored based on the pustule area and inoculum density. In terms of whether sporulating uredinia formed, the 19 isolates showed seven different patterns to the tested poplar clones. The majority of the rust isolates infected P. nigra ‘P3090’ and ‘Vereecken’, P.␣nigra × P. deltoides ‘Casale’ and ‘Tasman’, P. tacamahaca × trichocarpa ‘36’ and ‘Balsam Spire’, and P.␣trichocarpa ‘Blom’. Populus trichocarpa × P. deltoides ‘69039/4’ was infected by only three isolates collected from southern England. No visible symptoms appeared on P. alba  × P. tremula‘Tower’ and P.␣trichcarpa × P. deltoides × P. deltoides‘76028/5’ in inoculations with M. larici-populina isolates. Populus alba × P.␣tremula ‘Tower’ was infected only by M. populnea. When M. larici-populina isolates were tested using AFLP, no differences were found either between isolates from different geographical regions or between those having ‘narrow’ spectrum of virulence and those showing ‘wide’ spectrum of virulence on the tested clones. The results suggest that the UK rust populations possess virulences which were found in races E1, E2, E3 and E4 in continental Europe and that rust having virulence patterns similar to race E4 has occurred in UK poplar plantations since 1996.