Investigations in the regulation of common bunt (Tilletia tritici) of winter wheat with regard to threshold values, cultivar susceptibility and non-chemical protection measures

The objectives of the present study were the determination of treatment threshold values for control of common bunt of wheat (Tilletia tritici) and evaluation of alternative seed treatments. Wheat seed inoculated with the fungus was sown in fields at three sites in Germany from 2002–2004. Seeds of three cultivars – ‘Naturastar’ (highly susceptible), ‘Aron’ (moderately susceptible), and ‘Batis’ (highly susceptible) – were first inoculated with 20, 100 and 1000 spores/seed and treated with Tillecur®, a natural plant strengthener, or hot water before planting. Untreated inoculated seeds were used as control. Bunt infection rates in the resulting wheat plants varied according to inoculum size, cultivar and treatment method, with additional variation between the respective years and sites. Regarding inoculum size, 20 spores/seed sufficed for bunt development in the highly susceptible cultivars. In the moderately susceptible cultivar, 1000 spores/seed were required in the first year compared to only 20 spores/seed in the following years. Tillecur® provided the most effective bunt control: the number of infested ears was low to nil for all sites and inoculum sizes. Hot water was less effective and its effect was not significant except at the high inoculum level. Field data and calculations of the theoretically possible spore load suggest that low-level bunt infection represents a general danger. We conclude that treatment thresholds for control of common bunt must vary depending on the susceptibility of cultivar and the purpose of the harvested seed. When used for seed production, measures for prevention of disease accumulation are imperative. In those cases, we recommend a treatment threshold of one spore/seed for susceptible wheat cultivars and 20 spores/seed for less susceptible cultivars. (Published in: Journal of Plant Diseases and Protection 2007:114(6), S.269-275)