First record of Alternaria petroselini sensu lato causing leaf blight on parsley in Australia

Abstract

During 2005surveys for parsley diseases in Australia, an Alternaria sp. was isolated from leaf blighted plants in Chambers Flat, Queensland, and Clyde, Victoria. Symptoms included chlorotic and necrotic lesions on the leaves that spread down the stems in badly affected plants. The fungus sporulated abundantly on moist incubated leaves and was transferred directly to V8 agar and grown under lights. The fungus produced abundant alternarioid conidia that were borne singly, subspherical to oval and 40–80 × 20–25 µm. Alternaria petroselini and A. selini are similar species that cause leaf blight of parsley. They are distinguished by whether the conidia are predominantly subsphaerical or oval (Simmons, 1995). However, it has been suggested that these two species could be synonyms based on molecular evidence (Pryor, 2002; Pryor & Bigelow, 2003). The conidia in our cultures were very variable, and although they favoured A. selini, given the inability to be totally confident in a precise identification, this fungus was identified as A. petroselini sensu lato. Neither A. petroselini, nor A. selini have been previously recorded in Australia. Cultures have been lodged in herbarium VPRI. Pathogenicity experiments were conducted. The fungus was grown on V8 agar at room temperature under lights for one week. The agar plate was flooded with sterile deionised water supplemented with the surfactant Tween 80 (1 drop Tween 80 per 100 mL deionised water). A conidial suspension (1 × 105 conidia per mL) was sprayed onto curly-leaf parsley plants (Petroselini crispum cv. Afro) until runoff. Control plants were sprayed with sterile deionised water supplemented with Tween 80. Plants were covered in plastic bags and placed in a growth chamber with a 16/8 light cycle, day temperature set at 25°C and a night temperature of 15°C. After 7 days typical leaf blight symptoms could be seen. Plants were heavily blighted 18 days after inoculation. The fungus was reisolated by directly removing conidia from the leaf surface. This disease has been recorded in England, the USA and Saudi Arabia (Farr et al., No Date). It is probably widespread in eastern Australia, but has gone unnoticed until these surveys. Economic losses were observed on the Queensland property, but the damage was very minor in Victoria.