Melampsora euphorbiae, a new rust disease found on Euphorbia rigida in Turkey

Abstract

Euphorbia rigida occurs widely in Turkey and is a weed of gardens and uncultivated areas. It is found throughout the Mediterranean basin and the Middle East, occurring from Turkey and Iran through to Portugal and Morocco. During surveys performed in early summer 2003, a severe rust disease was found on E. rigida, in the Malatya province of eastern Anatolia, where the plant is common. The severity of the disease notably increased by mid-August when many plants were covered with uredinia. Many leaves died before normal flowering commenced. Uredinia occurred mostly on the lower surface of leaves (occasionally above) and on stems measuring 0.5-2 mm across, becoming a dark colour when mature. The urediniospores had a wall of uneven thickness and varied in shape, including spherical, ellipsoidal, pyriform and other irregular forms, 19-23 x 24-33 μm. Colourless paraphyses with walls of uneven thickness were also present, 7-10 pm to 30-38 μm. Based on these characteristics and measurements, the fungus was identified as Melampsora euphorbiae (Kaneko & Hiratsuka, 1984). This appears to be the first record of M. eupborbiae on natural populations of E. rigida in Turkey. E. rigida is also planted in Europe as a garden ornamental, but there are no known records of rust infection. The rust has been recorded previously on E. lagascae in Spain (Villalobos & Jellis, 1992) and E. esula in northern China (Wang et al., 1994). The fungus has been screened for use as a biological control agent against the weeds E. esula and E. cyparissias in the USA (Bruckart & Dowler, 1986). There is little indication that E. rigida is seen as an invasive plant anywhere and while M. euphorbiae has clear potential as a biological control agent against other Euphorbia species, the rust disease poses more of a threat to the horticultural trade of E. rigida at present.