Powdery mildew caused by Erysiphe sp. on Lagerstroemia indica newly reported in Turkey

Lagerstroemia indica is one of the most widely used landscape trees on the Mediterranean coast of Turkey. A long period of striking summer flower color, attractive fall foliage and good drought tolerance, all combine to make this plant a favourite small tree for either formal or informal landscapes. In the spring of 2008, during a survey of diseases of ornamental trees and shrubs, severe outbreaks of powdery mildew on this plant were noticed in eight parts of Izmir. White superficial mycelia with abundant sporulation developed on both leaf surfaces, on the non-lignified parts of the stems and on the surface of the fruits, forming thin, irregular colonies (Figs. 1-3). Infections often caused leaf distortions, withering and reduced growth. Conidiophores were unbranched and measured 36-75 x 6-10 µm. Foot cells were cylindrical, sometimes slightly flexuous, followed by one or two cells and measured 18-33 x 6-10 µm. Appressoria were mutilobed to moderately lobed, often in pairs. Conidia were ellipsoid or cylindrical, produced singly, lacked distinct fibrosin bodies and measured 21-45 x 12-21 µm, producing germ tubes at the basal end (Fig. 4). Chasmothecia were not observed but the above characteristics are fully consistent with Oidium subgenus Pseudoidium, the anamorph of Erysiphe. Previous records of powdery mildew on Lagerstroemia indicate that it is most likely to be Erysiphe australiana (syn. Uncinuiella australiana) (Braun 1987; Liberato & Barreto, 2004). Specimens are preserved in the Herbarium of the Plant Protection Research Institute at Izmir.

Pathogenicity was confirmed on detached healthy shoots, inoculated by touching them with powdery mildew-infected leaves. Non-inoculated shoots served as controls. Both inoculated and non-inoculated shoots were kept with ends in water within plastic bags in the laboratory where the temperature ranged between 18 and 30°C. After 12 days, typical powdery mildew symptoms appeared on the leaves of inoculated plants. No symptoms were observed on control plants.

Powdery mildew of L. indica has been recorded in Argentina, Brazil, China, Japan, Switzerland, UK, USA and Venezuela (Jones & Baker, 2007; Liberato & Barreto, 2004; Shi & Mmbaga, 2006). This is the first record of powdery mildew disease caused by E. australiana on L. indica grown in Turkey.