Epidemic outbreaks of powdery mildew caused by Leveillula taurica on Capparis spinosa in Turkey

Caper (Capparis spinosa L ) is a common native plant in Turkey, with edible flower buds and fruits. Powdery mildew was observed on wild caper in Sanlıurfa and Gaziantep provinces, within the southeastern Anatolia district of Turkey in 2002 and 2003. The disease was detected on 30-35% of plants in 2002 and on 86-93% of plants visited in 2003. White superficial mycelium on leaf surfaces was first detected in early summer and spread rapidly in summer and autumn. Colony development was more common on the leaf underside, but frequently both surfaces of leaves were completely covered by a thick layer of persistent mycelium by the end of August. Colonies also developed to some extent on petioles, pedicels and branches. Underneath the mycelium, chlorotic or dead tissue was conspicuous on leaves. Severe infection led to premature defoliation. Appressoria developed on endogenous mycelia within leaf tissue. Conidiophores were produced mostly on the underside of leaves and were straight and generally unbranched, and produced conidia singly. Conidia were lanceolate (primary conidia) or ellipsoidal (12-18 x 39-81 µm). Numerous cleistothecia were produced amid the mycelium and were yellow to dark brown or black in colour; mostly round to broadly ovate and 176-192 µm in diameter. They contained 3-27 broadly oval to ellipsoidal asci (25-45 x 53-98 µm), each containing two ascospores (15-23 x 25-44 µm). Appendages of cleistothecia were colourless and mycelial, irregularly branching, 35-80µm in length. Based on asexual and sexual morphology, the cause of this powdery mildew was determined as Leveillula taurica (Lev.) (Braun, 1987). A voucher specimen was deposited at the U.S. National Fungus Collection (BPI) and assigned BPI number 843766.

Pathogenicity tests were performed on 2.5-month old healthy caper plants grown from root cuttings. Leaves were inoculated by overhead shaking of naturally infected plants having abundant sporulation. Inoculated plants were then incubated in a growth chamber at 27±2°C with 16h photoperiod and 45-65% relative humidity. Symptoms similar to those on naturally infected plants occurred 10 days after inoculation.

Very recently L. taurica has been recorded in Turkey for the first time (Kurt et al., 2003). This is however the first published report of L. taurica infecting C. spinosa. Unpublished observations of powdery mildew associated with C. spinosa from Pakistan, Palestine and Iraq (P.M. Kirk, Pers. Comm.) suggest that this is a significant disease of caper, found throughout the Near East.