Epidemiology of Tilletia indica Teliospores in Regulated Wheat Fields in Texas

To examine the epidemiology of Tilletia indica teliospores in naturally infested soils from wheat fields in both Karnal bunt-regulated regions in Texas, soil was grid sampled from fields that were bunted-kernel positive for Karnal bunt in 1997, 2001, both years, or never. Aliquots of soil from each point were pooled, and teliospores were extracted using a size-selective sieving-sucrose centrifugation method. Teliospores were enumerated microscopically, and low quantities (< 8 per 25 g of soil) were identified in 14 of 15 fields sampled from the regulated regions of Texas, including fields that have never tested positive for bunted kernels, indicating a widespread distribution. No teliospores were isolated from the single field examined outside of the regulated regions. The percent clay was significantly, negatively correlated with the baseline teliospore number and the estimated (extrapolated) number of teliospores per sample, indicating a potential impact of soil composition on teliospore survival. The latter factor was also significantly, positively correlated to the number of times a field had tested positive.

Survival of Teliospores of Tilletia indica in Arizona Field Soils

The survival of teliospores of the Karnal bunt of wheat pathogen, Tilletia indica, was determined in field plots in Tucson, AZ. Two methods were used to test viability during a 48-month period in which 21-μm-pore-size polyester mesh bags of teliospore-infested soil were buried in irrigated and nonirrigated field plots at two sites. One method determined the total number of viable teliospores in a soil sample, regardless of whether or not they could be extracted from the soil using a sucrose centrifugation technique. The total number of viable teliospores declined over time in both irrigated and nonirrigated field plots and in the same soils in the laboratory. Based on nonlinear regressions, total number of viable teliospores decreased from 55.7% at time zero to 9.7 and 6.7% for nonirrigated and irrigated field soils, respectively, in 48 months. Total number of viable teliospores in soil in the laboratory decreased from 55.7 to 34.0% after 48 months. The second method determined germination percentages of teliospores extracted from the soil samples by means of a sucrose centrifugation technique. Based on linear regressions of transformed data, germination of teliospores extracted from irrigated and nonirrigated field soils, and control (laboratory) soil, significantly decreased over time. The rate of decrease in germination was significantly greater for teliospores from irrigated field plots than from nonirrigated plots and the laboratory soil. At time zero, 55.7% of teliospores germinated, and by 48 months, average germination of teliospores extracted from soil in nonirrigated plots had decreased to 13.6% compared with 4.4% in irrigated plots and 36.8% for teliospores in the laboratory control. Regression over time of total number of viable teliospores accounted for more of the overall variability than did regression over time of germination percentages of extracted teliospores. Neither field site nor soil depth had any effect on total number of viable teliospores or on teliospore germination percentages.