Volume 59 Number 2 Article 12
Year 2005 Month 4
Title: Evaluation of Scab (Venturia inaequalis) Severity on 54 Cultivars of Apple in an Unsprayed Common Planting
Authors: H.A. Quamme, C.R. Hampson and P.L. Sholberg
Abstract:
Seventy apple (Malus × domestica Borkh.) genotypes were evaluated in a common planting to identify clones with
partial resistance to apple scab [Venturia inaequalis (Cke.) Wint.] that could be used in a durable scab resistance
breeding program.
Fifty-four cultivars and 14 breeding selections of cultivated apple, and one clone each of Malus
floribunda and Malus sikkimensis were evaluated.
Two to ten replicate trees per genotype were propagated on
dwarf rootstocks and planted into raised beds covered with black plastic at Agassiz, BC, Canada, a site with severe
annual scab epidemics.
No fungicides were applied.
Field resistance to natural scab infection was rated on a 0 to 5
scale for each plant for three consecutive years.
Scab-susceptible standards such as 'Delicious', 'Mclntosh', 'Royal
Gala' and 'Idared' had severe annual infection.
Genotypes carrying Vr Vm or V scab resistance genes were free of
leaf and fruit scab, as was Malus floribunda 821, indicating that scab races 5, 6 and 7 were absent from the plot.
'Regine', 'Rebella', 'Resi', 'Rewena' were notable for the absence of all visible leaf disease symptoms.
Among
cultivars with presumed polygenic resistance, 'Akane', 'Anis Aily', 'Antonovka', 'Bramley's Seedling', 'Chehalis',
'Discovery', 'Generos', 'Golden Reinette', 'Golden Russett', 'MargiF, 'Peypring Cerueuko' and 'Wolf River'
were free of sporulating scab every year. 'Frumos de Voinesti', 'Lord Lambourne', 'Spartan', 'Gravenstein' and
'Lodi' were less susceptible than 'Mclntosh', but some trees had moderate to high infection (ratings 3 to 4) in some
years. 'Goldgelbe' and 'Gladstone' initially appeared resistant, but became infected in the third year, and may not
have durable resistance.
Summerland apple introductions 'Sinta', 'Stirling', 'Silken', 'Chinook', '8S6923'(Aurora
Golden Gala™), and advanced selection BC 8S-26-50 were highly susceptible to scab, 'Creston' was moderately
susceptible, and 'Golden Sentinel' and 'Scarlett Sentinel' were resistant.
Several breeding selections of'Akane' ×
'Discovery' parentage originally selected for their fruit quality also appeared to be resistant to scab.
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