GROWTH STAGE-SPECIFIC RESISTANCE OF WINTER RYE TO MICRODOCHIUM-NIVALE AND FUSARIUM SPP IN THE FIELD ASSESSED BY IMMUNOLOGICAL METHODS

Microdochium nivale and various Fusarium spp, cause severe diseases at all cereal growth stages. To investigate the successive colonization of the basal parts of winter rye in the field, 12 inbred lines were inoculated artificially with M. nivale and 11 with F. culmorum at one location across 2 yr for each pathogen. Arbitrarily sampled shoot or stem bases were assessed for fungal protein content in the host tissue by indirect enzyme-linked immunosorbent assay (ELISA) at seven growth stages from the beginning of tillering (EC 21) to full maturity (EC 91). Foot rot lesions were rated on a 1 to 9 scale at milk ripening. For M. nivale, the highest protein content and best genotypic differentiation were found in EC 21 shortly after snow melt. During further growth of the plants, M. nivale protein content decreased substantially and increased again between anthesis and full maturity. In contrast, Fusarium spp. showed a continuous increase in host tissue colonization from tillering to full maturity. In the early growth stages, fungal protein content was highly variable between years. Genotypic differentiation for resistance was significant at the earliest (EC 21) and a late (EC 75) host growth stage for M. nivale and at all growth stages tested for Fusarium spp. Heritability estimates reached the highest value at EC 21 for the M. nivale ELISA (h(2) = 0.59) and at milk ripening for the Fusarium spp. ELISA (h(2) = 0,91). Microdochium nivale and Fusarium spp, all caused foot rot symptoms at milk ripening leading to a mean foot rot rating of 3.3 and 3.8, respectively. No significant correlation existed between the resistance at early and adult-plant growth stages. For resistance to Fusarium spp., moderate to high genotypic correlations (r = 0.64-0.86) were found only among the adult-plant heading, anthesis, and milk ripening stages. Selection for adult plant resistance to Fusarium foot rot is not feasible during early host growth stages due to strong host genotype-growth stage interactions. Accordingly, resistance to M. nivale at early host growth stages (EC 21 and EC 25) cannot be used to predict resistance to M. nivale foot rot at milk ripening.