First Report of Leaf Rust of Blueberry Caused by Pucciniastrum vaccinii in Argentina.

During March, 1997, a leaf rust was observed on Vaccinium corymbosum L. cv. Bluegold in Argentina. Leaf lesions began as chlorotic flecks that expanded and developed into necrotic spots with several uredinia. The typical orange pustules of the disease developed mostly on the abaxial sides of leaves. Urediniospores were elliptical to obovate (17 to 28 × 11 to 23 μm) and finely verrucose. Telia were round, covered by the epidermis, slightly elevated, and brown to black. Teliospores were sessile and oblong to columnar (7 to 11 × 14 to 17 μm) with two or more vertical cell walls, and were smooth and brown. Urediniospore and teliospore morphology and dimensions were consistent with the description of Pucciniastrum vaccinii (G. Wint.) Jørst (syn. P. myrtilli Arth.) (1). A pathogenicity test was conducted with 18-month-old cv. Bluegold plants. Fully expanded leaves were sprayed, using a hand-held sprayer, with freshly collected urediniospores (1 mg of spores per ml of 0.05% water solution of Tween 20), covered with plastic bags, and placed in a growth chamber at 20°C for 48 h with 12 h of light per day. The plastic bags were then removed and the plants mantained in a greenhouse. After 10 days, orange rust pustules similar to the original symptoms developed on all plants. As the rust was not reported on ornamental Ericaceae in Argentina, and hemlock, the alternate host, is not present in the area, it is suggested that P. vaccinii is cycling on blueberry. This is the first report of P. vaccinii on blueberry in Argentina. Reference: (1) P. R. Bristow and A. W. Stretch. 1995. Pages 20-22 in: Compendium of Blueberry and Cranberry Diseases. F. L. Caruso and D. C. Ramsdell, eds. American Phytopathological Society, St. Paul, MN.