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 comm on) following inoculation with conidia of either Mycosphaerella gramin icola or Phaeosphaeria nodorum. Significant variation was observed amo ng genotypes for each resistance component. Genotypes resistant to Myc osphaerella graminicola had long LP and low S but variable IF. Genotyp es resistant to Phaeosphaeria nodorum had low IF, long LP and low to m oderate 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. Com binations of genotypes were sought for which one genotype may contribu te to a reduced disease severity for S. nodorum and the other genotype may contribute to a reduced disease severity for S. tritici in mixtur es. Such combinations of genotypes were rare.