Alternaria alternata causes pre-harvest discolouration in Backhousia myrtifolia leaf Sarana Sommano & Daryl C. Joyce & Son Quang Dinh & Bruce D’Arcy Received: 4 March 2011 /Accepted: 13 July 2011 /Published online: 26 July 2011 # Australasian Plant Pathology Society Inc. 2011 Abstract Backhousia myrtifolia is an Australian native plant cultivated for cut flowers and foliage. A leaf browning syndrome, with unknown cause, became prob- lematic for the floriculture industry in the years 2003–2004. Alternaria alternata was isolated consistently from brown leaf lesions on potted nursery plants and pathogenicity was confirmed by Koch’ s postulates. This is the first report of A. alternata on B. myrtifolia that is a possible cause of leaf discolouration in B. myrtifolia. Keywords Australian native plant . Browning . Cut flower Backhousia myrtifolia is an Australian native plant grown in subtropical Queensland and New South Wales. Ruptured leaf and flower tissues give off a cinnamon-like aroma, which accounts for the plant’ s common name of “Cinnamon Myrtle”. This species has been cultivated in recent years as a cut flower crop. It has aesthetically beautiful dark green leaves and lime-green to white flowers which pleases Japanese flower markets (Lim-Camacho et al. 2006). However without knowing the clear causes, its cut foliage and flowers suffer from browning and/or blackening spots, which later expand to become brown lesions approximately 0.5 cm in diameter after harvest and during storage at low temperature. The symptoms were initially detected in northern Australia (QLD), but have since more been found in southern regions (NSW) (Ekman et al. 2008). This has become a problem for the export industry. Chilling injury and dehydration during storage were initially suggested as main triggers of this discolouration (Ekman et al. 2008). Brown to black spots on the leaves of potted B. myrtifolia plants were first observed during July to September 2008 on 4-year-old B. myrtifolia potted stock (n =80) at the nursery on The University of Queensland’ s Gatton campus (27º33′S, 152º20′E). Approximately 30% of plants showed discolouration on their fully developed leaves. The visible discolouration developed on the leaf surface as tiny spots that expanded to brown lesions, which then covered the whole leaf surface (Fig. 1). Leaves with brown lesions were harvested and transferred to the laboratory in a plastic container lined with wet paper towels. Leaf tissue of approximately 2.5 mm 2 was cut from the edge of lesions which included both discoloured and adjacent healthy tissues. These cut tissues were surface sterilised in 75% (v/v) ethanol for 60 s, dried, then placed onto PDA media in Petri dishes and incubated at room temperature (~25°C) in a black light (Sylvania® black light- blue F 18 w/BLB-T8, Japan) chamber on a 12 h on-off cycle. Five–ten pieces from the same leaf were placed on the Petri dishes and there were 5 replicate dishes for each of S. Sommano (*) : D. C. Joyce : B. D’Arcy School of Agriculture and Food Sciences, The University of Queensland, Gatton, Qld 4343, Australia e-mail: s.sommano1@uq.edu.au D. C. Joyce Department of Employment, Economic Development and Innovation, Agriscience Queensland, PO Box 5083, SCMC, Nambour, QLD 4560, Australia S. Q. Dinh Department of Primary Industries, Biosciences Research Division, Knoxfield Centre, Private Bag 15, Ferntree Gully Delivery Centre, Vic 3156, Australia Australasian Plant Dis. Notes (2011) 6:64–66 DOI 10.1007/s13314-011-0022-x