New Disease Reports
New Disease Reports (2005) 11, 50.
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New report of loose smut (Ustilago syntherismae) on Digitaria sanguinalis in Spain

M.T. Mas 1*, A.M.C. Verdú 1 and J. Girbal 2

*maite.mas@upc.edu

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Accepted: 04 Jul 2005

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, NE Spain, 46° 12' N and 4° 33' E). Groups of infected plants (4-5 individuals) of Digitaria 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 stereo microscope at this stage showed that the inflorescence was initially infected by the rachis of racemes, where sori (irregular to confluent) could be observed (Fig. 1). 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 (Fig. 2).

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 x 12.5 µm diameter (n=50, range 7.5-12.5 x 9-16 µm), echinulate and brown in colour (Figs 3 & 4), with a thick wall about 0.5 µm. Based on these morphological features, the organism was determined as U. syntherismae (Vánky, 1994). A sample was deposited in the BCB - Mycotheca of the Universitat Autònoma de Barcelona (ref. 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 determined by Thuemen (1880) as Ustilago rabenhorstiana on Panicum sanguinale. Vánky (1999) indicates U. rabenhorstiana is a synonym of U. syntherismae, just as Panicum sanguinale is synonymous to D. sanguinalis. This is believed to be the first report of U. syntherismae on Digitaria sanguinalis in Spain since the 19th Century. Further research is required to investigate the current distribution of the smut in Spain.

Figure1+
Figure 1: Beginning of the sporulation of Ustilago syntherismae on the rachis of Digitaria sanguinalis racemes
Figure 1: Beginning of the sporulation of Ustilago syntherismae on the rachis of Digitaria sanguinalis racemes
Figure2+
Figure 2: Ustilago syntherismae on Digitaria sanguinalis inflorescence. Note, spikelets replaced by a blackish-brown spore mass
Figure 2: Ustilago syntherismae on Digitaria sanguinalis inflorescence. Note, spikelets replaced by a blackish-brown spore mass
Figure3+
Figure 3: Spores of Ustilago syntherismae
Figure 3: Spores of Ustilago syntherismae
Figure4a+Figure4b+
Figure 4: Scanning electron micrograph of Ustilago syntherismae on Digitaria sanguinalis showing globose echinulate spores
Figure 4: Scanning electron micrograph of Ustilago syntherismae on Digitaria sanguinalis showing globose echinulate spores

Acknowledgements

The authors would like to thank the Servei de Microscí²pia Electrí²nica (UAB) for technical assistance.

References

  1. Almaraz T, 2002. Bases corológicas de Flora Micológica Ibérica. Números 1766-1932. In: F Pando, ed. Cuadernos de Trabajo de Flora Micológica Ibérica, Vol. 17. Madrid, Spain: Dep. Publicaciones CSIC, No. 1923.
  2. 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, 150-151.
  3. Vánky K, 1994. European Smut Fungi. Stuttgart, Germany: Gustav Fisher Verlag.
  4. Vánky K, 1999. Taxonomical studies on Ustilaginales. Mycotaxon 73, 135-161.
This report was formally published in Plant Pathology

©2005 The Authors