GROWTH STAGE-SPECIFIC RESISTANCE OF WINTER RYE TO MICRODOCHIUM-NIVALEAND 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 in oculated artificially with M. nivale and 11 with F. culmorum at one lo cation across 2 yr for each pathogen. Arbitrarily sampled shoot or ste m bases were assessed for fungal protein content in the host tissue by indirect enzyme-linked immunosorbent assay (ELISA) at seven growth st ages 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 differentiati on were found in EC 21 shortly after snow melt. During further growth of the plants, M. nivale protein content decreased substantially and i ncreased again between anthesis and full maturity. In contrast, Fusari um 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 fo r 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 s pp, all caused foot rot symptoms at milk ripening leading to a mean fo ot 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 correlat ions (r = 0.64-0.86) were found only among the adult-plant heading, an thesis, 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, re sistance to M. nivale at early host growth stages (EC 21 and EC 25) ca nnot be used to predict resistance to M. nivale foot rot at milk ripen ing.