Urapan (Fraxinus udhei) dieback, a new disease associated with a phytoplasma in Colombia

The urapan tree was introduced into Colombia around 50 years ago and has been planted along the streets of cities and rural areas throughout the Andean zone. Previously referred to as Fraxinus chinensis, recent taxonomic studies indicate that its correct name is F. udhei; a native species of Mexico (E. Wollander, personal communication). Symptoms of urapan dieback include yellowing of leaves, little leaves and unusual patterns of regrowth of crowns and, less commonly, on trunks of mature trees, which often give the foliage a tufted appearance. These symptoms are similar to those of ash yellows, a phytoplasma disease found in North America and especially the north-eastern USA (Sinclair & Griffiths, 1996). Urapan trees with similar dieback symptoms have been observed in Bogota, Medellin, Pereira, Manizales in Colombia and in Quito, Ecuador. Using both DAPI staining and PCR, phytoplasma infection was detected in urapan trees affected with dieback, with samples from these trees consistently yielding amplified phytoplasma DNA by PCR using the universal 16S rDNA primers P1/Tint and R16/R2 (Smart et al., 1996; Lee et al., 1993). A phytoplasma-specific product of 1200 base pairs (obtained using primer pair R16/ R2) was sequenced and shown to share 94% homology with ash yellows (AshY3) gene 16sRNA (GenBank accession number AF105315). There is very little information on diseases of F. udhei but there is no indication of any other causes of the symptoms characteristic of ash yellows. In a May 2000 survey of 50 trees from seven localities in Bogota, 48% had moderate symptoms, and 52% were severely affected by the disease. This is the first confirmed record of ash yellows occurring outside North America and has considerable significance for Fraxinus species which are widely planted in urban and rural settings throughout the Andean range as well as natural stands of F. udhei in Mexico.