Abstract
Following a 2004-outbreak of Karnal bunt in an Arizona wheat field where infection had not been detected in recent years, the population and viability of Tilletia indica teliospores in surface and subsurface layers of soil were monitored over a four-year period. The field was seeded with two parallel 1.8 m × 190 m strips of wheat, 11 m apart and the remainder planted in non-host barley. Thirty-eight 1.22 m2 wheat plots were harvested and seed examined for infection. Several times throughout each season soil samples were taken from each of 25 points throughout the field. Teliospores extracted from subsamples of each soil sample were examined to estimate the number of teliospores per gram soil and germination percentage. The average (SD) infection observed for each of the four consecutive seasons was 7.05 (4.6), 2.89 (5.5), 0, and 0.004% (0). The average number of teliospores recovered per gram of soil during the first sampling was 36 and 39 for the 0.5 cm deep (surface) and 5.5 cm deep (subsurface), respectively, with an average teliospore germination of 29%. By the last season, the average numbers of teliospores recovered were 5 and 2.5 per gram of soil, respectively, with an average germination of 1.0%.
Highlights
Karnal bunt of wheat, caused by the fungus Tilletia indica Mitra, was first detected in the United States in wheat fields in the state of Arizona in 1996
Following a 2004-outbreak of Karnal bunt in an Arizona wheat field where infection had not been detected in recent years, the population and viability of Tilletia indica teliospores in surface and subsurface layers of soil were monitored over a four-year period
It is possible that changes in teliospore numbers and viability could differ between artificially infested soil and natural field populations, this study suggests that valid conclusions can be drawn from both artificially infected containerized soil and T. indica naturally infested soils
Summary
The two-hectare experimental field was established under Federal and State permit to pursue a number of research studies involving viability teliospores. In November, “Cavalier” spring wheat was seeded in two parallel strips, 1.8 m wide, 11 m apart, 190 m long, 11 m from the road and 35 m from the adjacent field. Strips were planted with a commercial planter at a seeding rate of 3.3 g per meter of furrow, approximately 2.5 cm deep. Areas not planted in wheat were seeded with a non-host VNS spring barley in an attempt to limit the edge effect during the study. Fields were initially irrigated at a rate of approximately 15 cm of water per m2. Subsequent fertilization and irrigation followed local best management practices used on the farm
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