First report of leaf rust of blueberry caused by Thekopsora minima in China.
Blueberry (Vaccinium corymbosum) is a popular fruit in Sichuan Province, China. In 2015, leaf rust-like symptoms were observed in several blueberry fields in Wenjiang, Shuangliu, Dujiangyan and Yaan. Blueberry leaf rust symptoms were first observed in April, causing extensive defoliation in the following months. Random field surveys were performed in early October to determine the incidence of the disease in Wenjiang by assessing 20 leaves from 100 plants of each cultivar. Leaf rust incidence was estimated to be 87.2, 5.1, 3.5, and 0.0% on Sharpblue, Misty, Bluegold, and O'Neill, respectively. Symptoms on the upper adaxial part of the leaves appeared as small, yellow spots, later turned necrotic, and eventually covered large areas of the leaf. On the abaxial part, numerous small water-soaked brown spots appeared, and stacks of powdery sori were produced with uredinia full of urediniospores. The spots were 2-10 mm in diameter with uredinia. Based on morphological characteristics, DNA sequence analysis and pathogenicity tests, the causal agent was identified as T. minima. Previously, blueberry leaf rust caused by T. minima has been reported in Mexico, Michigan, Delaware and New York in the USA, Japan, and South Africa. Tsuga spp. plants are able to serve as alternate hosts for T. minima and are necessary for the completion of the rust's life cycle. However, Tsuga spp. plants were not found in surrounding diseased blueberry fields in this study. This is thought to be the first report of blueberry rust disease caused by T. minima in China.