Leaf rust was first observed in 1997 on southern high-bush blueberry (Vaccinium corymbosum L.) cvs. Sharpblue, Gulfcoast, and Misty, in two production fields in Huelva Province of Andalucía, in southwestern Spain. Depending on environmental conditions, these cultivars may remain evergreen in this region. In early spring, when the temperature reaches 20°C, typical yellowish-orange pustules first appear on the abaxial side of older leaves and later on new leaves. Leaf lesions began as chlorotic dots and developed into necrotic spots. As much as 85% of the fruits on symptomatic bushes showed pustules on the scar area. Multiple infection cycles were possible during the growing season as urediniospores reinfect leaves at the end of summer. Disease was considered of minor importance, but defoliation occurred when spotting was severe. Urediniospores were yellowish-orange, abovoid to elliptical (15 to 26 × 10 to 20 μm), with a thick, slightly roughened wall and a central pore. Telia formed in the lower epidermis and were smooth and brown. Teliospores (7 to 10 × 12 to 15 μm) were sessile, oblong to columnar, with two or more cross walls. Urediniospore and teliospore dimensions and morphology agree with the description of P. vaccinii, (G. Wint.) (1). A pathogenicity test was carried out with 2-year-old ‘Sharpblue’ and ‘Star’ plants. Expanded leaves were sprayed with freshly collected urediniospores suspended in a 0.05% solution of Tween 20 in water; plants were covered with plastic bags for 48 h and held in a chamber at 20 to 25°C in the shade. After 10 days, yellowish-orange pustules, similar to the original symptoms, developed on 80% of inoculated leaves of ‘Sharpblue’, while ‘Star’ plants remained symptomless. Leaf rust has not been reported on Ericaceae in Spain. The evergreen state of some southern high-bush cultivars in this area could allow the pathogen to overwinter as urediniospores. To our knowledge, this is the first report of P. vaccinii on blueberry plants in Spain.
Reference: (1) P. R. Bristow and A. W. Stretch. Pages 20--22 in: Compendium of Blueberry and Cranberry Diseases. F. L. Caruso and D. C. Ramsdell, eds. American Phytopathological Society, St. Paul, MN, 1995.
