Australian diagnostic protocol for Tilletia indica
Tilletia indica (EPPO A1 List) does not occur in Australia and it is acknowledged that any introduction would disrupt access to global markets for Australian wheat. To ensure an adequate state of preparedness for a potential incursion to Australia, a national diagnostic protocol was prepared in 2003, to detect and identify T. indica. In addition, in February 2004 a shipment of Australian wheat was rejected on the grounds that it contained teliospores of T. indica (which was later demonstrated to be a misidentification). Therefore, in March 2004, surveys were done on Australian wheat consigned for export using the national diagnostic protocol. T. indica was not found but results showed moderate levels of common smuts: Tilletia caries, T. laevis and Urocystis agropyri, and very low levels (less than 6 teliospores/150 g grain) of an unidentified dark, tuberculate-spored Tilletia in approximately 60% of tested samples. Comparison with herbarium specimens enabled identification of the majority of the teliospores as Tilletia ehrhartae, a smut known to infect only Ehrharta calycina (perennial veldtgrass, Poaceae) a common species in southern Australia. A smaller number of teliospores were identified as T. walkeri, a smut of Lolium spp. It is stressed that T. ehrhartae and T. walkeri both resemble T. indica and that this may lead to misidentification, in particular with T. ehrhartae which is commonly present as a contaminant in Australian wheat grain.
EPPO note: the EPPO diagnostic protocol includes a pictorial guide to distinguish 3 tuberculate-spored Tilletia species: T. indica, T. walkeri and T. horrida which are known contaminants of wheat seeds, but not of T. ehrhartae.
Pascoae IG, Priest MJ, Shivas RG, Cunnington JH (2005) Ustilospores of Tilletia ehrhartae, a smut of Ehrharta calycina, are common contaminants of Australian wheat grain, and a potential source of confusion with Tilletia indica, the cause of Karnal bunt of wheat. Plant Pathology 54(2), 161-168.
EPPO (2004) EPPO Standard PM 7/29(1) Diagnostic protocols for regulated pests. Tilletia indica (available online). http://archives.eppo.org/EPPOStandards/PM7_DIAGNOS/pm7-29(1).pdf