Submitted to: XII Biennial Workshop on Smut Fungi Proceedings
Publication Type: Proceedings
Publication Acceptance Date: August 1, 2000
Publication Date: August 15, 2000
Interpretive Summary: Bunt fungi on grass crops such as wheat, rice, and millet are difficult to identify yet their accurate identification is extremely important for the risk-free export and import of these commodities throughout the world. At present the identification of bunt fungi is based primarily on host as well as the shape, size, and ornamentation of the thick-walled teliospores. This paper presents molecular differences between groups of species of bunt fungi including the isolates that were lumped together as one species. Three groups of species could be defined based on molecular characteristics. One group includes isolates of bunt fungi that occur on wheat and some wild grasses. A second group consists of isolates on rice while a third group includes isolates on millet and other grasses. This research clarifies the confusion surrounding isolates of bunt fungi identified as one broadly conceived species. In addition, it provides the molecular basis for accurately defining and identifying the bunt fungi of grass crops.
Technical Abstract: Neovossia barclayana Bref. was originally described in 1895 on Pennisetum triflorium Nees. (P. orientale Rich) from Simla, India, and transferred to the genus Tilletia by Saccardo and Sydow in 1899. Its generic placement is still an issue and Tilletia and Neovossia have not been clearly delimited (for discussion of Tilletia vs. Neovossia see Castlebury and Carris 1999. All of these fungi produce globose to subglobose, light to dark brown teliospores, which range from approximately 15 to 40 m in diameter. All have echinate to truncate spines, which may appear to curve around the spore, surrounded by a gelatinous sheath, giving the appearance of a tinted band at the periphery of the teliospore (Dur n and Fischer, 1961; Zundel 1953). In 1952, Tullis and Johnson synonymized these names under Neovossia barclayana on the basis of experimental host range and teliospore morphology. Recent studies (Castlebury and Carris 1999; Pimentel et al. 1998) have suggested that molecular differences exist between isolates from rice and isolates from wild grasses. Previously, teliospore morphology was characterized for taxa within this complex (Castlebury 1998). In this study, the internal transcribed spacer (ITS) regions of the nuclear rDNA repeat unit were sequenced for 26 isolates identified as Tilletia barclayana based on host and/or teliospore morphology as well as other taxa within the genus Tilletia to determine both phylogenetic placement and conspecificity of taxa. Results of the previous morphological study will also be discussed.