Author
 |
Goates, Blair |
|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/1/2006 Publication Date: 6/1/2006 Citation: Goates, B. 2006. Anomalous and new epidemiological relationships of seed diseases caused by tilletia species. Phytopathology 96:S132 Interpretive Summary: Early studies of the relationship between smut fungi and the diseases they cause in small grains are part of the foundation of plant pathology. Results of some recent studies of infection of wheat do not have major effects on disease development but are interesting from the standpoint of epidemiology. For example, normal infection of winter wheat by Tilletia controversa, which causes dwarf bunt, is initiated when spores at the soil surface germinate and produce hyphae that infect above ground tissue of seedlings during winter. However, slight infection occurs after inoculating seed, which appears to result from spores germinating beneath the soil. And, T. indica causes Karnal bunt in wheat after air-borne fungal structures called sporidia infect florets during heading, but unexpectedly, slightly more disease is produced in spore infested soil when healthy seed is planted as compared to diseased seed. T. tritici and T. laevis are essentially identical wheat pathogens that both cause common bunt, but for unknown reasons one species is often dominant over the other in different geographic regions. An important factor that relates to epidemiology of seed diseases of wheat, rice and rye grass caused by T. indica, T. horrida, and T. walkeri, respectively, has been discovered recently. Air-borne sporidia of these species initiate infection of florets leading to disease. Sporidia are considered to be fragile and short lived, but recent studies have demonstrated that sporidia are durable and viable after several weeks of very dry conditions in laboratory and field environments. After humid conditions are restored, new sporidia rapidly regenerate and produce hyphae capable of infecting plants. This indicates that sporidia could survive for extensive periods of time under dry conditions and then rapidly regenerate and infect plants under humid rainy conditions that are associated with the diseases. The sporidia appear to be a primary component of survival of the pathogen within a season. Technical Abstract: Early studies of the relationship between smut fungi and the diseases they cause in small grains are part of the foundation of plant pathology. Results of some recent studies are difficult to explain. For example, dwarf bunt of winter wheat, caused by Tilletia controversa, is initiated when teliospores at the soil surface germinate and produce hyphae that infect above-ground tissue of seedlings during prolonged low temperatures during winter. However, slight infection can occur after inoculating seed. And, T. indica causes Karnal bunt in wheat after air-borne sporidia infect florets during heading. Unrelated to this infection, slightly more disease is produced in teliospore laden field soil when healthy seed is planted as compared to diseased seed. T. tritici and T. laevis are essentially identical seed- and soil-borne wheat pathogens that both cause common bunt, but it is unknown why one pathogen is commonly dominant over the other in different geographic regions. Forcibly discharged air-borne sporidia are the infecting agents of the floret-infecting fungi T. indica, T. horrida, and T. walkeri. Although the thin-walled sporidia are considered to be fragile and short lived, recent studies have demonstrated that sporidia are viable after several weeks of very dry conditions in laboratory and field environments. After humid conditions are restored, new sporidia that have produced hyphae capable of infecting plants are commonly generated within 18 hours. |
