Components of resistance to Mycosphaerella graminicola and Phaeosphaeria nodorum in spring wheats

Infection frequency (IF), latent period (LP) and sporulation rate (S) were assessed on 23 genotypes (cultivars, breeding lines and parents) in the field and 36 genotypes in the glasshouse (with 22 being in common) following inoculation with conidia of either Mycosphaerella graminicola or Phaeosphaeria nodorum. Significant variation was observed among genotypes for each resistance component. Genotypes resistant to Mycosphaerella graminicola had long LP and low S but variable IF. Genotypes resistant to Phaeosphaeria nodorum had low IF, long LP and low to moderate S. IF and S were independent while a negative correlation was observed between LP and S for Mycosphaerella graminicola only. LP was most consistently correlated with field response. Components measured in the field better discriminated resistant genotypes from others. Combinations of genotypes were sought for which one genotype may contribute to a reduced disease severity for S. nodorum and the other genotype may contribute to a reduced disease severity for S. tritici in mixtures. Such combinations of genotypes were rare.