The effect of powdery mildew inoculum pressure and fertilizer levels on disease tolerance in spring barley

The effect of inoculum pressure on disease tolerance was studied on a range of spring barley genotypes by manipulating the quantity of spores being de posited on field plots from surrounding plots. Genotypes included previousl y selected tolerant and non-tolerant types and the modifying effects of fer tilizer levels were also studied. Under low fertilizer and 'normal' inoculu m pressure and especially high fertilizer and high inoculum pressure condit ions, where host and pathogen development were likely to be near equilibriu m, designation of barley genotypes as tolerant or non-tolerant was more rel iable than under the other conditions tested. Single trials were not reliab le for designating tolerance.