In February 2004, a shipment of Australian wheat was rejected by an importing country on the grounds that the shipment allegedly contained ustilospores of the Karnal bunt pathogen, Tilletia indica. Subsequently this led to an extensive audit in Australia of all wheat export consignments. Results of this audit found that in approximately 60% of the samples there were moderate levels of the common smuts: Tilletia caries, Tilletia laevis, and Urocystis agropyri, and very low levels of an unidentified dark, tuberculate-spored Tilletia that resembled Tilletia indica. Comparison of herbarium specimens eventually led to the identification of this unknown species as Tilletia ehrhartae, a smut fungus known to infect only Ehrharta calycina (perennial veldt grass), a grass species common in southern Australia and California.
The presence of T. ehrhartae in export consignments has implications for diagnosticians as it further complicates the already difficult process of differentiating tuberculate ustilospores of species other than Tilletia indica potentially found in wheat shipments. This article describes T. ehrhartae in detail and includes criteria for differentiating it from the other similar-looking smut species. The article also suggests that importing countries need to be cautious before identifying tuberculate ustilospores as T. indica, and should consider the other candidate species that may be present in the grain’s country of origin.
Of particular importance are: Tilletia walkeri (on ryegrass), T. horrida (on rice), T. barclayana (on Panicum spp. and other hosts), T. ehrhartae (on Ehrharta calycina), T. rugispora (on Paspalum spp.), T. eragrostis (on Eragrostis spp.), T. cathcartae (on Poa spp.) and T. inolens (on Agrostis and Deyeuxia spp.).
For the whole article, see:
Pascoe I. G., Priest, M. J., Shivas, R. G. and J. H. Cunnington. 2005. Ustilospores of Tilletia ehrhartae, a smut of Ehrharta calycina, are common contaminants with Tilletia indica, the cause of Karnal bunt of wheat. Plant Pathology Vol. 54: 161-168.
Or online: http://www.blackwell-synergy.com/links/doi/10.1111/j.1365-3059.2005.01145.x/abs/