First Report of Pustula tragopogonis, the Cause of White Rust on Cultivated Sunflower in Southern Germany. M. Thines, R. Zipper, and O. Spring, Institute of Botany, University of Hohenheim, Stuttgart, Germany. Plant Dis. 90:110, 2006; published on-line as DOI: 10.1094/PD-90-0110C. Accepted for publication 23 October 2005.

Pustula tragopogonis (Pers.) Thines (2), formerly known as Albugo tragopogonis (Pers.) Gray, causes white rust on some members of the Asteraceae. It has been reported to attack cultivated sunflower in several parts of the world, for example, North America (1) and South Africa (3), but has not been previously reported on sunflower in Germany. During June 2003, the first diseased plants were observed in a sunflower field near Stuttgart, where sunflowers were grown as ornamentals. During 2004, P. tragopogonis was found in several ornamental sunflower fields in southern Germany. In some cases, P. tragopogonis co-occurred with Plasmopara halstedii (Farlow) Berl. & De Toni on the same plants. After a cold winter, the first diseased plants for 2005 were observed during June in the area around Stuttgart. The percentage of affected plants in the sunflower fields varied considerably, ranging from 20 to 80%. Only small lesions with oospores could be found on petioles and stems of infected plants. The typical spots with white blisters were observed mostly on leaves in the upper half of the plants, but also occurred on the bracteoles of the flower heads. Spots were chlorotic on the upper side of the leaf and exhibited whitish pustules on the lower side of the leaf. Pustules were concentrated around the margins of the leaves, but also were observed scattered on the whole lower surface. Light and scanning electron microscopy, as well as polymerase chain reaction and internal transcribed spacer sequencing were applied to identify the attacking pathogen as P. tragopogonis. Infection tests under laboratory conditions also proved the pathogenicity of the attacking agent to oilseed sunflower. Since the pathogen has survived the harsh winter months of early 2005 and appeared in three consecutive seasons, the disease seems now to be established in southern Germany and is expected to spread into other regions.

References: (1) T. J. Gulya et al. Plant Dis. 86:559, 2002. (2) M. Thines and O. Spring. Mycotaxon 92:443, 2005. (3) P. S. van Wyk et al. Helia 22:83, 1995.