Resistance of the Vineland series of apple rootstocks to fire blight caused by Erwinia amylovora

The fire blight 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 two experim ents and compared with the scion cultivar 'Delicious'/M.9. Direct inoculati on of rootstock liners with E. amylovora using a syringe was made in a nurs ery and the length of the fire blight lesions was measured. All the 'V.' ro otstocks were more resistant than M.26, with V.3, VA, 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 'Del icious' scion displayed low resistance in both studies. These data indicate that the fire blight resistant responses could be grouped into the followi ng 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 resis tance(M.26). The Vineland series of apple rootstock may afford greater resi stance to fire blight infections than commercially available M.9 or M.26 ro otstocks. Further research is required to determine how this resistance mig ht be conferred to the scion, particularly for cultivars that have a high s usceptibility to E. amylovora.