First report of sugar beet crown wart disease caused by Urophlyctis leproides in Egypt

Leaf and crown wart, marbled or beet root tumour are some of the common names given to a disease of sugar beet ( Beta vulgaris ) caused by Urophlyctis leproides (Physoderma leproides). It was first reported in Algeria in 1894 (Trabut, 1894). Since then, the disease has been recorded in Argentina, Italy, Spain, United Kingdom, Palestine and the USA ( Whitney , 1971). In Egypt, the disease was observed during harvest (2003, 2004, 2005) at three locations in the Nile Delta (Behira, Gharbia and Kafr El-Sheikh) on a range of sugar beet cultivars (Gloria, Kawmera, Oscar poly, Othus poly and Pleno). Disease incidence (DI) was less than 1% in 2003, 1-2% in 2004 and 3% in 2005. Although the DI is currently low, if the trend observed over the last few years continues, the disease could reach epidemic levels in the near future.

Figure 1 : Crown symptoms showing different sized galls. Figure 2: Cross section of a gall.

The disease exhibited typical symptoms on root crowns and occasionally on petioles and leaf blades. Galls on leaf blades and petioles are greenish brown and have a rough appearance. Affected leaves are malformed. On the crown, galls range in size from 1 cm to (most commonly) 8-10 cm. These galls are spherical, rough and are attached to the host by a narrow base (Fig. 1). Gall colour was variable, ranging from shades of green through yellow to brown depending on the age of plant cultivar. Galls occurred singly or coalesced to form complexes. Sections made through a crown gall reveal cavities filled with thick-walled sporangia (resting spores) surrounded by thickened wall (Fig. 2 & 3). Sporangia were light brown, spherical to ovoid or concave (25 ±5 – 40 ±5 µm) in diameter (Fig. 4) ( Ruppel , 1995). As the gall decomposes, resting sporangia are released into the soil. Soil surveys were carried out in the affected areas revealed that resting sporangia were detected.

Figure 3: Scanning electron microscope cross-section of a gall. Figure 4 : SEM Close up of U. leproides resting spores.

Koch’s postulates were fulfilled. Twenty seedlings of B. vulgaris cv. Gloria were inoculated with 10⁵ resting spores per ml and incubated 22 ± 2°C and 1000 lux of continuous fluorescent light for 48 h, followed by 14 h light and 10 h dark. Uninoculated plants were used as a control. Symptoms appeared on the test plants after 11 days and sporangia were reisolated from the mature gall tissues ( Mahmoody et al., 1997). No symptoms were observed on uninoculated controls.

This is the first report of sugar beet crown wart disease ( U. leproides) affecting B. vulgaris in Egypt.