Pathogenic variation in populations of Drechslera teres f. teres and D. teres f. maculata and differences in host cultivar responses

Abstract

The current study examined the variability in the pathogenicity of populations of Drechslera teres f. teres and D. teres f. maculata (the net and spot forms of D. teres) from Ireland and northern Europe. A population of progeny isolates from a mating of net and spot forms was also examined. Significant variation in virulence was found both between and among net form and spot form isolates (p<0.001). In the Irish population, significant differences were found between the net and spot forms, with the spot form isolates more virulent (p<0.05). Progeny isolates were significantly more virulent than net form or spot form populations (p<0.001). Significant differences were found in cultivar reactions, with cv. Botnia most susceptible to both forms of the pathogen (p<0.001). Cultivar Boreal 94145, although quantitatively resistant, was found to be very susceptible to both forms of the pathogen and to progeny isolates. Cultivars CI 5791, CI 2330 and CI 9819 were all less susceptible to infection by both forms, but were more susceptible to spot form isolates. Significant correlations were found between whole plants and detached leaf experiments for the net form isolates only (p<0.001). This study illustrates the importance of including both net form and spot form isolates in resistance studies and the need for a clearer understanding for the genetic basis of resistance to the net and spot forms. It also highlights the limitations of using a detached leaf assay for screening of net blotch of barley.