Submitted to: Bunts and Smuts of Wheat
Publication Type: Proceedings
Publication Acceptance Date: 6/12/1998
Publication Date: N/A
Interpretive Summary: Each year many billions of dollars of agricultural losses are caused by fungal diseases of crop plants. Bunt and smut diseases of wheat and other grass crops have resulted in an estimated $2 billion loss in crop yield and lost export markets in 1996 and 1997 alone. The discovery of Karnal bunt on wheat in the United States precipitated a crisis particularly in the wheat export market due to the strict quarantine that had been placed on this fungus. This situation was exacerbated by the mistaken identification as Karnal bunt of a second bunt fungus that occurs on ryegrass. The teliospores of these fungi are difficult to differentiate. For this study teliospores of the fungus causing Karnal bunt on wheat and the bunt fungus on ryegrass were carefully compared using light and scanning electron microscopy. It was discovered that these two entities can be differentiate using these techniques. Data on teliospore morphology and SEM of teliospore ornamentation are presented that illustrate the differences among the bunt fungi occurring on wheat and ryegras. This paper provides the means to distinguish the Karnal bunt fungus from similar looking fungi on grass hosts. These results will be useful to federal plant quarantine officials, state extension agents, and seed technologists.
Technical Abstract: Tilletia indica, the causal agent of Karnal or partial bunt of wheat, produces large, brown, tuberculate teliospores. Morphologically based identification of similar looking species of Tilletia can be difficult without accurate knowledge of the host, especially when few teliospores are present. In this study, herbarium and fresh specimens of T. indica, T. horrida, T. lolii, T. eragrostidis, and an apparently undescribed Tilletia from bunted Lolium spp. seeds were examined. Teliospores were characterized using light and scanning electron microscopy. Shape, size, ornamentation and color of the teliospores were analyzed. Mature T. indica teliospores, ranging from 30.2-63.8 um diam, were dark red-brown, often opaque, with a densely ornamented exospore. Teliospores of the Tilletia from Lolium were 26.2-44.4 um diam, ranging in color from pale yellowish-or golden-brown to dark brown, with a more coarsely ornamented exospore. Tilletia horrida and T. eragrostidis, with spores ranging from 21.9-41.4 u and 26.9-43.3 um respectively, and T. lolii were distinguished from T. indica mainly by exospore ornamentation. Molecular confirmation will be helpful in cases when the host is uncertain and certain morphological characters overlap or when the stage of maturity of the teliospore is not known.