Evaluation of Greenhouse Inoculation and Scoring Methods to Assess Common Bunt Resistance in Wheat

Common bunt, caused by Tilletia caries and T. laevis, is a fungal disease of wheat that can cause significant yield and quality losses. Field screening for common bunt is often hampered by environmental factors and is limited to one evaluation per year. In contrast, greenhouse screening potentially enables two to three assessments per year. We evaluated three greenhouse inoculation methods and two scoring techniques using two highly susceptible cultivars ('Apogee' and 'Red Bobs') and four moderately susceptible cultivars ('Fielder', 'LCS Star', 'SY Capstone', and 'UI Platinum'). In the first inoculation method, seeds were inoculated with a teliospore suspension and were planted on the same day. In the second method, inoculated seeds were allowed to dry and were planted 3 days later. In the third method, seedlings were inoculated at the three-leaf stage by spraying a teliospore suspension directly onto the leaves. Disease incidence (percentage of infected spikes per plant) and severity (percentage of infected spikelets) were measured at physiological maturity. Seedling inoculation by spraying produced the lowest infection levels across all cultivars, with overall incidence ranging from 7.91 to 19.11% and severity from 5.01 to 13.69%. The two seed inoculation methods showed greater disease symptoms, with incidence ranging from 49.35 to 98.02% and severity from 43.04 to 94.06%, with no significant differences between the methods. Severity and incidence were correlated (0.95 to 0.97) across the two seed inoculation methods. Thus, the seed inoculation methods were superior to the seedling spray inoculation method for the response of wheat germplasm to common bunt infection. This finding was validated with a set of wheat cultivars and differential lines. This study underscores the importance of considering inoculation techniques in screening germplasm to select for common bunt resistance in wheat.