First Report of a Putative New Erysiphe sp. Causing Powdery Mildew on Avocado in Florida

The avocado (Persea americana Miller) brings in an estimated $100 million annually to the state of Florida. While its largest threat in recent years continues to be laurel wilt, caused by Raffaelea lauricola, there is a myriad of other diseases affecting avocado. Although powdery mildew on avocadoes is rare, the novel species Podosphaera perseae-americanae has been recently reported in Indonesia (Siahaan et al. 2016). In April 2017, leaf samples from P. americana cv. ‘Waldin’ grown in a greenhouse exhibiting symptoms typical of powdery mildew were submitted to the Florida Extension Plant Diagnostic Clinic in Homestead, FL. Symptoms included white powdery colonies growing on abaxial surfaces of younger leaves, while older damage included veiny, chlorotic lesions. Other cultivars in the same greenhouse including ‘Toro Canyon’, ‘Duke 7’ and ‘Dusa’ did not appear to be susceptible to powdery mildew. Microscopic observations revealed hyaline, ellipsoid to cylindrical conidia measuring 25 to 40 × 15 to 40 μm (a...