Resistance of the Vineland series of apple rootstocks to fire blight caused by Erwinia amylovora.
The fire blight (caused by E. amylovora) resistance of several Malus rootstocks (V.1, V.2, V.3, V.4, V.5, V.6, V.7, and VR.50 in the Vineland series, and several commercially recognized M.7, M.26, M.9E, G.16, B.9 and O.3) was evaluated in greenhouse and nursery experiments and compared with the scion cultivar 'Delicious'/M.9. Direct inoculation of rootstock liners with E. amylovora using a syringe was made in a nursery and the length of the fire blight lesions was measured. All the 'V.' rootstocks were more resistant than M.26, with V.3, V.1, V.6, V.7, V.2 having the greatest resistance, whilst in the second experiment, six rootstocks (M.7 > V.6 > V.3 > V.1 > V.2 > V.4) were shown to be more resistant than M.26. The 'Delicious' scion displayed low resistance in both studies. These data indicate that the fire blight resistant responses could be grouped into the following four categories: high resistance (V.5, V.7), intermediate resistance (V.1, V.6, V.2, M.7, B.9), low resistance (G.16, V.3, M.9, V.4), and no resistance(M.26). The Vineland series of apple rootstock may afford greater resistance to fire blight infections than commercially available M.9 or M.26 rootstocks. Further research is required to determine how this resistance might be conferred to the scion, particularly for cultivars that have a high susceptibility to E. amylovora.