Pestalotiopsis chamaeropis causing leaf spot disease of round leaf mint-bush (Prostanthera rotundifolia) in Australia Azin Moslemi 1 & Paul W. J. Taylor 1 Received: 26 May 2015 /Accepted: 7 September 2015 /Published online: 14 September 2015 # Australasian Plant Pathology Society Inc. 2015 Abstract Pestalotiopsis chamaeropis was isolated from ne- crotic leaf spots of round leaf mint-bush -Prostanthera rotundifolia (Lamiaceae) in Melbourne, Australia. Pathogenicity was confirmed by obtaining similar symptoms after inoculation of the young leaves and stems with a spore suspension of P. chamaeropis. Molecular analysis of the ITS, tef1 and TUB genes, individually and combined, identified the pathogen as P. chamaeropis. The pigmentation of the median cells, number of apical and basal appendages were similar to the type isolate of P. chamaeropis. This is the first report of P. chamaeropis being a pathogen of round leaf mint-bush in Australia. Keywords ITS . tef1 . TUB . Apical . Type isolate Prostanthera rotundifolia (Lamiaceae) is a native mint-bush plant growing in cool and temperate regions of Australia such as South Australia, Victoria, New South Wales, north and east of Tasmania (Fulton 2000; Conn 1998). The oil extracted from P. rotundifolia contains hexane, ethyl acetate and methanol which are antimicrobial properties and inhibit growth of bac- teria such as Bacillus subtilis, Staphylococcus aureus and Escherischia coli (Dellar et al. 1994). There are very few reports of plant pathogens causing dis- eases in P. rotundifolia. Formerly, Phytophthora cinnamomi was isolated from mint-bush but the plant was recognised as a resistant host and showed no disease symptoms (Barker and Wardlaw 1995). In 2013, young and newly grown leaves and stems of mint-bush plants growing in the Systems Garden at the University of Melbourne, Australia were found showing brown, water-soaked and sunken round lesions (predominate- ly on the underside), darker in the margins, light brown-red in the centre. Chlorotic tissue occurred on the surface of the leaves but not underside. Typical symptoms of the disease were collected from the mint-bush plant and transferred to the laboratory in plastic bags for culturing and isolate identification. Leaves were surface sterilised by immersing for 30 s in 80 % ethanol, before transferring to 1 % a.i. sodium hypochlo- rite for 1 min, followed by washing in sterilised water. Sterilised leaves were then blotted with sterilised paper towel, then 2 mm 2 of tissue from the margin of the lesion with healthy tissue was excised and plated onto water agar (WA) and incubated for 4 days at 23–25 °C. Mycelia that grew out of the leaves were transferred onto potato dextrose agar (PDA) and incubated for a further 7 days. Single spored colonies were obtained from isolates which were grown on PDA and incubated for 10 days at 22–24 °C. A culture of the isolate was deposited at the Queensland Plant Pathology Herbarium (BRIP), Australia. Colony growth rate was measured for three PDA cultures at 2-day intervals. The isolate was also grown on synthetic poor nutrient agar (SNA) (Crous et al. 2009) with pieces of sterilized filter papers (double autoclaved at 121 °C for 20 min) on the surface of the agar to induce sporulation. Seven days after culturing, spores were mounted in lactic acid and the conidia shape and size measured. To confirm pathogenicity, twigs containing rosettes of young healthy leaves and stems were cut from a healthy plant; surface sterilised and then placed in plastic containers. Inoculations were by either spraying leaves with 10 4 spore/ mL, or by pipetting 20 μl of spore suspension onto both sides of the leaves. Containers were sealed then incubated at 23– * Paul W. J. Taylor paulwjt@unimelb.edu.au 1 Faculty of Veterinary and Agricultural Science, University of Melbourne, Melbourne, VIC 3010, Australia Australasian Plant Dis. Notes (2015) 10: 29 DOI 10.1007/s13314-015-0179-9