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In September 2004, smutted inflorescences of large crabgrass (Digitaria sanguinalis) were observed in an uncropped edge of an arable field at Torre Marimon (near Barcelona, north-east Spain, 46°12′ N, 4°33′ E). Groups of smut-affected plants (four to five individuals) of D. sanguinalis were detected forming small patches among apparently healthy individuals. The first visible disease symptom was a slight separation of the leaf sheath from the stem (at the flag-leaf level). An examination with a stereomicroscope at this stage showed that the inflorescence was initially infected at the rachis of racemes, where sori (irregular to confluent) could be observed. As the disease developed further it extended into the spikelets from the rachis, and the inflorescence became entirely replaced by spore mass. At this stage, the inflorescence appeared partially hidden by enveloping leaf sheath.

To determine the morphological characteristics, spores were removed with small forceps and mounted in water for examination by light microscopy. Ustilospores were globose or subglobose to ovoid, mean 10 × 12·5 µm diameter (n = 50, range 7·5–12·5 × 9–16 µm), echinulate and brown in colour, with a thick wall c. 0·5 µm. Based on these morphological features, the organism was identified as Ustilago syntherismae (Vánky, 1994). A sample was deposited in the BCB-Mycotheca of the Universitat Autònoma de Barcelona (reference BCB-Mycotheca Ust034).

There is only one previous citation of this smut species for Spain (Almaraz, 2002). However, this relates to herbarium material collected in 1875 in Málaga, and described by Thuemen (1880) as Ustilago rabenhorstiana on Panicum sanguinale. Vánky (1999) indicates that U. rabenhorstiana is a synonym of U. syntherismae, just as P. sanguinale is synonymous with D. sanguinalis. This is believed to be the first report of U. syntherismae on D. sanguinalis in Spain since the 19th century. Further research is required to investigate the current distribution of the smut in Spain.

Acknowledgements

  1. Top of page
  2. Acknowledgements
  3. References

The authors would like to thank the Servei de Microscòpia Electrònica (UAB) for technical assistance.

References

  1. Top of page
  2. Acknowledgements
  3. References
  • Almaraz T, 2002. Bases corológicas de Flora Micológica Ibérica. Números 1766–1932. In: PandoF, ed. Cuadernos de Trabajo de Flora Micológica Ibérica, Vol. 17. Madrid, Spain: Departamento de Publicaciones CSIC, no 1923.
  • Thuemen F, 1880. Liste des champignons que feu le Dr Wolffenstein a récoltés pendant un séjour a Malaga en Espagne, déterminés par F. de Thuemen. Revue Mycologique Recueil 2, 1501.
  • Vánky K, 1994. European Smut Fungi. Stuttgart, Germany: Gustav Fisher Verlag.
  • Vánky K, 1999. Taxonomical studies on Ustilaginales. Mycotaxon 73, 13561.