Phenotypic characterization of the rvi15 vr2 apple scab resistance
P. Galli, G.A.L. Broggini, C. Gessler, A. Patocchi
Recently, a new apple scab resistance was found in the apple accession GMAL 2473 and named Rvi15 (Vr2). The resistance reaction mediated by Rvi15 (Vr2) appeared on the upper surface of young infected leaves 7 days post inoculation (dpi) as browning of epidermal cells. Starting from 11 dpi, browning of mesophyll cells was also observed suggesting a gradual involvement of the different leaf tissues. The resistance reaction resulted in pinpoint pits similar to those observed in Malus accessions carrying the Rvi5 (Vm) or Rvi4 (Vh4) resistance, which are considered to induce the classical hypersensitive response (symptoms appearing at both epidermal and mesophyll level 2-3 dpi). When the timing of the reaction is considered, Rvi15 (Vr2) seems more similar to the Rvi7 (Vfh) resistance found in Malus floribunda 821, which results in pinpoint pits 6 dpi. However, size of the pinpoint pits, number of cells involved and accumulation of fluorescent compounds at the site of pathogen penetration are very similar between all four resistance reactions.