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Scab-resistant cultivars

Many scab-resistant cultivars have recently been released as a result of breeding programs in the United States. They were developed primarily for resistance to apple scab, but some are also resistant to cedar apple rust, powdery mildew, and fire blight. Disease resistance does not mean total freedom from pesticides, since none of these cultivars are immune to insect damage or summer diseases like sooty blotch or flyspeck. There are some new cultivars coming from Germany that will have multiple resistances to such diseases as powdery mildew and fire blight, among others. These are being marketed as “ReZista Series.” For a listing and images of many of the scab-resistant cultivars, go to http://fpath.cas.psu.edu/FIELD_DAY/field%20day%202006/Srcs.htm.

Earlier releases such as Prima and Priscilla were not well accepted because of poor fruit quality. Since their release, newer cultivars now available may have promise for commercial orchards. Following are comments on selected apple-scab-resistant cultivars (see also Table 1-6):

Crimson Crisp was named by the Purdue Rutgers Illinois cooperative breeding program. It was tested as Co-op 39. The medium to dark red fruit have a cream-colored, mildly acidic, coarse flesh. The fruit will store about 6 months in regular storage. In addition to apple scab they are moderately resistant to rusts, powdery mildew, and fire blight. Fruit matures around the middle to end of September and hangs well on the tree.

Dayton was released in 1988. Its fruit ripens about 4 weeks before Delicious. Fruits are large with a glossy red color. Reports indicate that maximum storage may only be one month. The tree is vigorous, with strong, upright-growing branches. It has good resistance to mildew and cedar apple rust and moderate resistance to fire blight. No trees of this cultivar have been planted in Pennsylvania for evaluation.

Enterprise (Co-op 30) was released in 1993 by the PRI program as a later-maturing, scab-resistant apple cultivar. Flesh is yellow, with a 75 percent red skin. Fruit is of good quality. Flavor is very good although on the tart or acid side. Enterprise matures around October 15 in southcentral Pennsylvania and about a week later in central Pennsylvania. The tree has a very vigorous growth habit. It is suggested for both homeowner and commercial trials. It is believed prone to corking, but this has been controlled in southcentral Pennsylvania plantings with standard calcium chloride programs.

Freedom (NY58553-1) is ready for harvest around the end of September. Fruits are large and their external appearance is not very good, having a rough-looking finish. This cultivar does not store well, having ripened unevenly on the tree. Suggested for home plantings only.

Galarina is a Gala-like apple that is resistant to apple scab and can be stored for longer periods. It was developed in France from a Gala and Florina cross. The medium-size fruit matures 1 to 2 weeks after Gala. The skin color is 65 to 100 percent orange-red over greenish yellow with flesh that is yellowish white. The flavor is aromatic and slightly tart. Trees are moderately vigorous.

GoldRush (Co-op 38) was released in 1993 by the PRI program and is resistant to apple scab. The tree is moderately vigorous with an upright growth habit. The fruit ripens very late. Its growing season may be too long to be planted from central Pennsylvania northward. Fruit quality is excellent, and fruit has an approximately 7-month storage period. Fruits are medium to large and have a spicy to slightly acid taste at harvest, becoming better after a period of 2 months in storage. For someone looking for a Golden Delicious type, GoldRush would work very well. Suggested for both homeowner and commercial trials.

Jonafree, released in 1979, ripens with Jonathan and has a 95 percent red overcolor much like Jonathan's, but it is less susceptible to fire blight and powdery mildew than Jonathan. Jonafree is a very hard apple that does not develop a good flavor until after a period of storage. This cultivar has very vigorous growth and tends to be a tip bearer as well as an alternate year bearer. May work for processing and for homeowner use.

Liberty (NY55140-19), released in 1978, is dark red and resistant to rusts, mildew, and fire blight. Its harvest date is the last week in September to the first week in October in State College, although one source indicates ripening is about 10 days after McIntosh. The fruit tends to be small and may require multiple pickings; flavor is better after storage. Japanese beetles favor this cultivar to the extent that extra sprays are needed to control the pest.

Nova Easygro was released in 1975 from Kentville, Nova Scotia. It is a large apple, red striped over green, somewhat like McIntosh but a deeper red. The calyx is partially open to closed. Flesh is cream-colored and of a medium coarse texture. Flavor is tart (like Jonathan). The tree is very vigorous and ripens somewhat unevenly. The quality of apples grown in State College has been fair to poor. Plantings in 1990 experienced a preharvest fruit drop. No longer recommended in Pennsylvania for either commercial or home use.

Novamac is a McIntosh type released from Kentville, Nova Scotia. In plantings at Rock Springs on M9 rootstocks, the trees have been very precocious and have been consistent croppers. The fruit looks and tastes like McIntosh. This cultivar holds promise for both backyard and commercial use in areas where McIntosh is grown. Severe preharvest fruit drop in 1994.

Nova Spy was developed in Nova Scotia as a scab-resistant “Spy-type” apple. It is a juicy, firm-fleshed red apple. It is moderately susceptible to rusts and only lightly susceptible to powdery mildew. It was developed in Canada from a cross between Nova Easygro and NY-44411-1. The fruit are attractive, moderate high quality, long keeping, and similar to Northern Spy. Fruit are medium in size, globose conical, and slightly ribbed. The flesh is creamy yellow, fine, very firm, crisp, and
juicy. The fruit mature between Delicious and Northern Spy. It is an excellent processing cultivar. The tree is upright and moderately vigorous.

NY-75414-1 is an advanced selection from Cornell, developed by crossing Liberty with Macspur. Fruit grown in central Pennsylvania are very dark red to almost purple and slightly resemble Macoun. It is harvested around the middle of September. In the NE-183 planting at Rock Springs, it is one of the weakest-growing trees.

Otava was developed in the Czech Republic from a cross between Sampion and Jolana. The globose and ribbed fruit matures with Golden Delicious and has yellow skin with a slight redorange blush. The flesh is yellow to cream with fine-grained texture, juicy, and has a sweet subacid flavor. It is resistant to apple scab and tolerant to powdery mildew.

Pixie CrunchTM was released in 2004 from the Purdue, Rutgers, and Illinois cooperative breeding program. The blushed dark red to purple fruit have a yellow flesh that is extremely crisp, medium to fine grained, and juicy. Storage life is at best 2 months. The flavor is moderately to mildly acid. Fruit size tends to be small (2.5 inches diameter), which may decrease its value as a commercial cultivar. It is immune to apple scab, susceptible to powdery mildew, and moderately susceptible to fire blight.

Pristine was released from the Purdue, Rutgers, Illinois breeding program in 1995. It is also moderately resistant to fire blight, slightly resistant to cedar apple rust, and resistant to powdery mildew. Fruit matures with Lodi and should be used as a replacement for Lodi. Plantings at Rock Springs have been very productive. Fruit color is green to yellow.

Redfree, released in 1981, is a red-skinned summer apple. Harvest is around the middle of August in State College (6 to 7 weeks before Delicious). Storage life is only about 2 months; shows moderate tolerance to fire blight and powdery mildew. Tree wood is very brittle and weak. Redfree tends to be a tip bearer like Rome Beauty. Suggested only for homeowner use and possibly roadside markets.

Rubinola is resistant to apple scab and powdery mildew and matures 10 days before Golden Delicious. The trees are vigorous. The cultivar was the result of a cross between Prima and Rubin. The fruit are medium to large, flat, globose, and with a skin that is bright red over most of the surface, although some russeting can occur. The flesh is yellow, firm, fine textured, juicy, and has a sweet aromatic flavor.

Scarlet O’Hara^TM was released in 2004 from the Purdue, Rutgers, and Illinois cooperative breeding program. It was previously tested as Co-op 25. It is a mid-season red apple that ripens one week before Delicious. The fruit are round to slightly conic. The overcolor is described as 75 to 90 percent medium red to orange with a green-yellow to yellow undercolor. The flesh is yellow to cream colored, firm, and crisp. The flavor is sweet to mildly subacid. The tree and fruit are field immune to scab, moderately resistant to powdery mildew, highly resistant to cedar apple rust, and highly susceptible to fire blight.

Sundance was released in 2004 from the Purdue, Rutgers, and Illinois cooperative breeding program. It was previously tested as Co-op 29. The pale yellow fruit are large and attractive. They have moderate stem-end russet. The flesh is medium to coarse, cream colored, and has a very firm and crisp texture. The fruit have good storage potential and mature about 2.5 weeks after Delicious. Fruit tastes best after about a month in storage. Sundance is moderately resistant to powdery mildew and highly resistant to cedar apple rust and fire blight. Full details on the cultivar can be viewed in HortScience volume 39 number 2.

Topaz was developed in the Czech Republic from a cross between the Czech apple cultivars Vanda and Rubin. Topaz is a medium to medium-large apple. The skin color is yellow overlain with a red and crimson flush. The flesh is crisp and cream colored. The trees are moderately vigorous and very precocious. Trees are resistant to apple scab and moderately resistant to powdery mildew. Fruit matures about 1 week after Golden Delicious.

Williams Pride was released in 1988, one of the earliest-ripening cultivars released. Matures approximately 1 week after Lodi; in our plantings has matured around the middle of August. The dark red fruits are large with a semi-tart flavor that is very good. May have uneven ripening requiring multiple pickings. Growth observations indicate that the tree is very willowy. Suggested for homeowner use and roadside markets. Shows a strong tendency toward bitter pit.

The Future of Scab-Resistant Cultivars
Many more cultivars are being developed and tested in Europe. The Czech Republic, Italy, France, and Latvia all have active breeding and testing programs. The limitations to obtaining these cultivars is the inability to import new plant materials without going through a lengthy screening process. The other limitation to the wide adoption of scab-resistant cultivars is that most of the cultivars only carry the Vf gene for resistance. Establishing solid plantings of Vf-resistant cultivars may cause a breakdown in resistance of scab protection. In Switzerland where they have been growing scab-resistant cultivars, it is recommended that even if the cultivar is scab resistant a minimum number of sulfur sprays be applied each year to prevent the buildup of apple scab populations that can overcome the Vf resistance.