First report of Alternaria leaf blight caused by Alternaria dauci on carrot in Turkey

During February and November 2003, severe foliage infection by the Alternaria leaf blight agent Alternaria dauci was observed on carrot (Daucus carota L.) plants growing in the Hatay province of Turkey. The disease was extensive, with between 73 and 85% of fields inspected in the region being affected. Disease incidence of 65 to 90 % was recorded in affected fields (Fig. 1A). The distribution of the disease in carrot fields was generally associated with high soil moisture levels, often corresponding to poor drainage. Severe foliar infections resulted in reduced root yields and decreased the effectiveness of mechanical harvesting. Initial symptoms first appeared on older leaves as irregularly-shaped, minute, dark brown-to-black spots, with yellow borders on the edge of the leaflet blade. As the disease progressed the lesions expanded, causing the leaflets to turn brown, shrivel and die (Fig.1B).

A fungus was consistently isolated from the margins of these lesions, onto potato carrot agar (PCA) amended with streptomycin sulphate, maintained at 26°C under a 12 h near ultra violet photoperiod. These isolates produced a carpet-like mycelial mat and abundant conidia in the dark. Conidia were usually solitary, rarely in chains of two, long, ellipsoid-to-obclavate, some smooth but mostly punctulate, dark olivaceous brown, with 5 - 11 transverse and 1 (rarely 2 - 3) longitudinal or oblique septa. The conidia measured 295 - 410 x 15 - 25 µm in size including a filamentous beak (200 - 300 x 5 µm) (Fig. 2A). The conidiophore was 25 - 85 x 5 µm in size, olivaceous brown, simple or 1 - 2 geniculate (Fig. 2B). These measurements corresponded to those previously published (Simmons, 1995). Pathogenicity tests were conducted on carrot seedlings (cv. Nanco) at the six-leaf stage, by spraying the lower leaves with a conidial suspension (1 x 104 spores per ml). Inoculated plants were covered with a polyethylene bag, incubated at 26°C for 2 days, and subsequently transferred to a growth chamber at 26°C, with a 16 h photoperiod. Disease symptoms developed within 10 days as light brown lesions on leaflet margins. The pathogen was re-isolated from inoculated leaves.

A. dauci has been previously reported on carrot in Israel (Netzer & Kenneth, 1969), The Netherlands (Konstantinova et al., 2002) and USA (Strandberg, 1983). This is the first report of this disease in Turkey.