First report of blueberry leaf rust caused by Thekopsora minima on Vaccinium corymbosum in Michigan.
Leaf rut symptoms have been noticed sporadically on nothern highbrush blueberry plants (Vaccinium corymbosum) in Michigan (USA) for the past 8 years. In 2009, leaf rust was seen in several cultivated blueberry fields and on greenhouse-grown blueberry plants in southwest Michigan. In 2010, leaf rust as widespread throughout western Michigan and particularly evident in autumn, sometimes resulting in premature defoliation. Blueberry cultivars Rubel, Jersey, Elliott, Liberty and Brigitta were the most commonly affected. Both the 2009 and 2010 growing seasons were characterized by above-average precipitation in early to mid-summer. Early symptoms on the adaxial leaf surface consisted of roughly circular yellow spots that later developed brown necrotic centres. Older lesions were more angular and sometimes sorrounded by a purplish border. In autumn, a "green island" effect was sometimes apparent arount the lesions. On the abaxial side, numerous yellow-to-orange rust pustules (uredinia) were visible. On the basis of morphological characteristics and sequence analysis of ITS, the pathogen was identified as Thekopsora minima. T. minima has been reported on black huckleberry (Gaylussacia baccata) in Michigan. This is thought to be the first report of T. minima on highbush blueberry in the state. T. minima has been reported on highbush blueberry in Delaware and New York, Japan, and South Africa.