Relationship Between Kernel Infection and Spike Infection of Wheat by Tilletia indica, Causal Agent of Karnal Bunt. M. H. Royer, Research Plant Pathologist, Foreign Disease-Weed Science Research Unit, USDA-ARS, Ft. Detrick, Building 1301, Frederick, MD 21701. J. Rytter, Laboratory Technician, Foreign Disease-Weed Science Research Unit, USDA-ARS, Ft. Detrick, Building 1301, Frederick, MD 21701. Plant Dis. 70:225-228. Accepted for publication 3 April 1985. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1986. DOI: 10.1094/PD-70-225.

Plants of the spring wheat cultivar Olaf were inoculated with pairs of monosporidial lines of Tilletia indica (= Neovossia indica) by injecting sporidial suspensions into the boot sheath enclosing the spikes or by drenching the exposed spikes that had emerged from the boot with sporidial suspensions. The number of bunted spikes per total number of inoculated spikes was not significantly different between the two inoculation methods. The percentage of bunted kernels per bunted spike for the boot-injection method (74%) was significantly different from that for the spike-drench method (59%). With the latter inoculation technique, more infected kernels occurred in spikes inoculated immediately after spike emergence from the boot than in spikes inoculated immediately prior to or at anthesis. Regression models were applied to the data to examine the relationship between bunted kernels and bunted spikes. There was a significant linear relationship between the percentage of bunted kernels per inoculated spike and the percentage of bunted spikes. Thus, a given incidence (number) of bunted spikes can be used to predict the incidence of kernel infection with artificial inoculation of Olaf wheat in the greenhouse. The regression models may be solved for different cultivars. The regression parameters may be useful indicators of differences in cultivar resistance as well as pathogen virulence across different stages of spike development.