Interpretation of sugarcane smut susceptibility trials

Susceptibility to smut disease in sugarcane is normally estimated in small plots raised from inoculated buds. Standardisation of inoculation techniques (particularly concentration of spores) and of measuring infection are shown to be important. Due to the variable pattern of symptom development and the statistical limitations of small sample numbers, assessment of infection must be made on a stalk basis to be meaningful. Parallel quantitative field survey data of major varieties during the Guyana epidemic has enabled inoculation tests to be related to natural infection to give thresholds of susceptibility below which a variety is unlikely to generate an epidemic, and which can therefore be considered safe for more extensive planting.