Components of partial resistance as criteria for identifying resistance

The components of partial resistance, incubation period, lesion area, latent period and sporulation were recorded on plants of six winter and two spring wheat cultivars which had been artificially inoculated with Septoria nodorum spores. Incubation period gave a guide as to how the cultivars would respond in the field to Septoria nodorum but statistical analysis showed that it could not be used alone to predict accurately the resistance of each cultivar to the pathogen. Average sporulation, however, could be used with more confidence for predicting the field resistance of the cultivars. From a regression analysis of NIAB rating versus incubation period, lesion area, latent period and sporulation, an equation was devised to obtain resistance indices for each cultivar. These resistance indices clearly reflected the NIAB ratings for the cultivars. It would therefore appear that resistance indices could be used as a pre-field evaluation method for identifying resistance to Septoria nodorum and thus be a valuable technique in breeding programmes.