Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/24/2004
Publication Date: 8/1/2004
Citation: Bonde, M.R., Nester, S.E., Olsen, M., Berner, D.K. 2004. Survival of tilletia indica teliospores in arizona field soils. Plant Disease. 88:804-810. Interpretive Summary: When Karnal bunt of wheat was discovered in the U.S. in 1996, it was necessary to determine how long the fungal pathogen spores survived in infested fields. This information was necessary in order for federal regulatory officials to make informed decisions on how long contaminated fields should be quarantined, and prohibited from planting wheat. To answer the question, small polyester mesh bags of Karnal bunt infested soil were buried at various depths in irrigated and non-irrigated field plots in Tucson, Arizona. During the next 42 months, the bags were recovered, and numbers of viable spores counted. Results showed that the fungus could survive at least 42 months in either irrigated or non-irrigated fields, survival was slightly better in non-irrigated plots, and soil depth had no effect. Conclusions from the study will allow an estimate of rates of decrease in viable pathogen propagules, and determination of when it is safe to again plant wheat. The improved techniques developed will be used to predict survival in other areas of the country and formulate control strategies if necessary.
Technical Abstract: Two methods were used to test germinability during a 42-month period in which polyester mesh bags of Tilletia indica teliospore-infested soil were buried in irrigated and non-irrigated field plots in Tucson, Arizona. One method determined the total number of viable teliospores (TNVT) whether or not teliospores could be extracted from the soil. TNVT declined over time in both field soils and in the laboratory. Based on non-linear regressions of TNVT, the percent viable teliospores decreased from 55.7% at time zero to 11.5% and 6.7% for non-irrigated and irrigated field soils, respectively, after 42 months. The second method determined germination percentages of teliospores extracted from soil samples by a sucrose centrifugation technique. Based on linear regressions of transformed data, germination of teliospores for all treatments significantly decreased over time. Rate of decrease was significantly greater for teliospores from irrigated field plots than from non-irrigated plots and the laboratory control. At time zero, 55.7% of teliospores germinated, and by 42 months, average germination of teliospores extracted from soil in irrigated plots had decreased to 6.2%, compared to 23.1% in non-irrigated plots, and 42.3% for teliospores in the laboratory control.