the Iowa State University Horticulture Farm near Ames, the research
team evaluated survival, yield, and fruit quality of 13 apple cultivars
that are genetically highly resistant to scab. The cultivars were
selected from the Purdue-Rutgers-Illinois breeding program and the
Cornell University program.
trial orchard, planted in 1993 on M7 rootstock, included 13 scab-resistant
cultivars and one scab-susceptible cultivar (Empire). Eight scab-resistant
cultivars were commercially available but not widely grown in Iowa,
while five scab-resistant cultivars have not yet been released commercially.
Each cultivar had 9 single-tree replications. Conventional disease
and pest control tactics were used in the trial orchard, since the
objective was to evaluate horticultural characteristics. The trees
were trickle-irrigated as needed.
summarizes survival and growth of the cultivars after 7 years (1993-2000).
Tree mortality was low; only 4 trees died in the planting year and
only one tree thereafter. Williams Pride, Dayton, and Co-op 29 were
among the most vigorous cultivars in terms of tree growth, while
Gold Rush and Coop 28 were among the least vigorously growing cultivars.
highest-yielding cultivars over four harvest seasons (1997-2000) were
Williams Pride, Liberty, Co-op 31, Gold Rush, and Redfree (Table
On the other hand, Co-op 28, Empire, CLR13T40, and Co-op 27 had the
lowest yields. Freedom,Williams Pride, Enterprise, and Co-op 29 produced
relatively large-size fruit, while Co-op 28 and Liberty produced the
smallest fruit. Pre-harvest fruit drop averaged more than 20% for
CLR13T40, Jonafree, Williams Pride, and Enterprise.