Genotypic structure of Monilinia populations in Western Australia two decades after incursion

In 1997, Monilinia fructicola and Monilinia laxa, fungi causing brown rot disease in stone fruit ( Prunus species), were identified from Western Australia for the first time. Up until then, Monilinia were quarantine species, and importation of stone fruits to W.A. was prohibited. After Monilinia was identified in W.A., importation of stone fruit from sources outside W.A. was progressively permitted. Today, Monilinia is present in all stone fruit production regions in W.A. The aim of this study was to determine if the genotypes responsible for the first incursion subsequently spread, or if new genotypes have since become established. ISSR markers were used to identify the genotype of isolates collected during the initial incursion event in 1997, and compare them with isolates collected subsequently. Eight M. fructicola genotypes were identified, including a monotypic one on a fresh peach imported from the USA. M. fructicola isolates collected during the initial incursion in 1997 and an isolate from cherry collected in South Australia in the same year were all of the same genotype, suggesting fruit or germplasm from S.A. as the source of the W.A. incursion. However, this incursion genotype appears not have persisted, with different genotypes subsequently becoming widely or locally established. Four genotypes of M. laxa were identified. In contrast to M. fructicola , the 1997 incursion genotype of M. laxa has become widely established in W.A., infecting both stone fruits and pome fruits.