ARS | Publication request: Nonsystemic Bunt Fungi-Tilletia Indica and T. Horrida. a Review of History and Biology

Submitted to: Annual Review of Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 11, 2006
Publication Date: August 10, 2006
Citation: Carris, L.M., L.A. Castlebury, and B.J. Goates. 2006. Nonsystemic Bunt Fungi " Tilletia indica and T. horrida: A Review of History, Systematics, and Biology. Annual Review of Phytopathology 44:5.1-5.21. (doi:10.1146/annurev.phyto.44.070505.143402)

Interpretive Summary: Within the fungi one group of species causing diseases of grasses especially cereal crops such as wheat and rice are called bunt and smut fungi. These fungi belong to the genus Tilletia and infect grasses either throughout the entire plant or only in localized parts of the plant. Two examples of economically important diseases caused by fungi that infect plants in localized parts are Karnal bunt of wheat caused by Tilletia indica and rice kernel smut caused by Tilletia horrida. Additional species of bunt fungi on non-economic host plants have been confused with these species as contaminants in export grain and seed shipments. This confusion has hindered trade dealing with these agricultural commodities. In this paper the history, biology and economic impact of Karnal bunt of wheat, rice kernel smut, and other bunt fungi are reviewed. Plant pathologists will use this review to understand the differences between these smut and bunt fungi that impact the international exchange of rice and wheat.

Technical Abstract: Tilletia indica, the Karnal bunt pathogen, was first reported in 1931 in India. Due to its quarantine status, Karnal bunt gained international prominence in 1996 after its detection in the southwestern United States. This discovery resulted in annual surveys of all wheat growing regions in the US, and put at risk the entire US wheat export market valued at approximately $5.5 billion. Due to similar morphology and etiology, Karnal bunt was thought to be closely related to the rice pathogen, T. horrida, and this misunderstanding significantly impacted the methods used to identify the Karnal bunt pathogen. The surprising discovery of T. walkeri, a previously unknown but widely dispersed bunt on rye grass (Lolium spp.), had a significant impact on APHIS regulations for the annual surveys. Tilletia walkeri is now recognized as the species most closely related to T. indica. Tilletia indica is more closely related to the other wheat bunt species, T. caries and T. laevis (common bunt of wheat) and T. controversa (dwarf bunt of wheat) than previously recognized, and T. horrida is only distantly related to T. indica. In this chapter, we present a brief historical perspective of T. indica, T. horrida and morphologically and biologically similar bunt fungi that infect their respective hosts at the floret stage and produce a localized or non-systemic infection. We also discuss the biology, etiology and economic impact of these species in contrast to the systemically infecting wheat bunts.