Variation Associated with Silk Channel Inoculation for Common Smut of Sweet Corn

Abstract

Efforts at breeding for resistance to common smut of maize (Zea mays), caused by Ustilago maydis, are hampered by the lack of a reliable and efficient method of inoculation. Silk channel injection is one of the most efficient methods of inoculating for ear galls but is less consistent than acceptable for accurate assessment of the response of genotypes. The objective of this study was to examine how the silk channel inoculation method can be modified to reduce variation while maintaining efficiency for large-scale field inoculations. Variation associated with inoculum concentration and variation among people inoculating were examined. Incidence and severity of symptomatic ears increased with inoculum concentration. Concentrations between 105 and 106 sporidia/ml are recommended. Variation among people was greater than variation among inoculum concentrations. Incidence and severity ratings were lower for people inexperienced at inoculating with U. maydis than for experienced people. Variation among people inoculating can be controlled by appropriate experimental design.