PRI Disease Resistant Apple Breeding Program

Co-op 1
Co-op 3
Sir Prize
Co-op 6
Co-op 7
Co-op 8
Co-op 9
Co-op 10
Co-op 11
Co-op 12
Co-op 14
Co-op 15
Co-op 16
Co-op 17
Co-op 18
Co-op 19
Co-op 20
Williams' Pride
Co-op 24
Scarlett O'Hara
Co-op 26
Co-op 27
Co-op 28
Pixie Crunch
Co-op 34
Co-op 35
Co-op 36
Co-op 37
Co-op 40
Co-op 41
Co-op 42
Co-op 44

HortScience 35(l):150-151. February 2000.

'Co-op 25' (Scarlet O'HaraTM) Apple

Jules Janick
Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, IN 47907-1165

Joseph C. Goffreda
Department of Plant Science, Rutgers-The State University of New Jersey, New Brunswick, NJ 08901-8520

Schuyler S. Korban
Department of Natural Resources and Environmental Sciences, University of Illinois, Urbana, IL 61801

Additional index words. Malus xdomestica, Venturia inaequalis, fruit breeding, apple scab

Received for publication 25 Jan. 1999. Accepted for publication 11 May 1999. Journal paper 16,000 of the Purdue Univ. Agricultural Experiment Station. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.

'Co-op 25 'is a midseason, red apple (Malus xdomestica Borkh.) that ripens 1 week earlier than 'Delicious', with high productivity, very good fruit quality, and excellent storage life. The tree is productive, moderately vigorous, spreading, and comes into bearing early. The fruit is 90% medium red, up to 76 mm (3 inches) in diameter when well-thinned, and is generally short-conic to round in shape (Fig. 1). The skin is smooth, slightly waxy, and semi-glossy. The fruit is delicately spicy, with a full flavor that combines sweetness and subacidity. Quality is best after 1 or 2 months in storage and has a storage life of over 7 months at 1° C in refrigerated storage. The tree is spreading and round-topped with some tendency for tip bearing but also bears on short shoots. The fruit is resistant to preharvest drop and hangs on the tree, even when overripe. There is a slight tendency for alternate bearing.

'Co-op 25' is the 14th apple cultivar developed by the cooperative breeding program of the Indiana, Illinois, and New Jersey agricultural experiment stations (Crosby et al., 1992). It will be sold under the trademarked name Scarlet O'HaraTM to emphasize its attractive appearance and spirited qualities but, like its namesake, with some controversial characteristics. It was released with the positive support of Mr. Ed Fackler of Rocky Meadow Orchard & Nursery, New Salisbury, Ind., a nurseryman who has championed its reliability of production and high dessert qualities.

'Co-op 25' carries the genetic factor Vf inherited from Malus floribunda Sieb. 821 that renders it highly resistant to the apple scab disease incited by Venturia inaequalis (Cke.) Wint. Scab resistance was evaluated by controlled greenhouse inoculation tests at the seedling stage followed by 25 years of observation under natural conditions for infection in the field in West Lafayette, Ind.; Urbana, Ill.; Cream Ridge, N.J.; and in trials at sites in the United States, Italy, France, and Australia. Based on field observations, the selection is moderately susceptible to cedar-apple rust incited by Gymnosporanium juniperi-virginianae (Schw.), moderately susceptible to mildew incited by Podosphaera leucotricha (Ell. & Ev.) Salm., and highly susceptible to fireblight incited by Erwinia amylovora (Buff.) Winslow. Because of an open calyx, the selection is highly susceptible to moldy core, a fungal disease of the seed cavity, often due to Alternaria sp., and as a result will require fungicidal sprays at bloom.


The original seedling was produced from crossing the New Jersey selection PCFW 2-134 as the seed parent with the selection PRI 669-205 as the pollen parent in 1971 at the New Jersey Agricultural Experiment Station, a cross that produced a number of outstanding seedlings. The complete pedigree is shown in Fig. 2. The seedling was screened for scab resistance at Purdue Univ. in 1972, and was planted in a permanent field location in May 1973 at the Clark Farm in West Lafayette, Ind., where it was designated CLR20T4 1. The seedling was selected in 1978 by E.B. Williams and carried the progeny designation PRI 2714-4 in our breeding records. It was released for testing as 'Co-op 25' in 1984 and was described in Purdue University Station Bulletin 456 (Williams et al., 1984).

Fruit and leaves of 'Co-op 25' apple

Fig. 1. Fruit and leaves of 'Co-op 25' apple.

Pedigree of Co-op 25

Fig. 2. Pedigree of 'Co-op 25' apple.


The following is a detailed description of the flowers, fruit, tree, and leaves based on Zielinski (1955) with color designations according to the 1966 Horticultural Colour Chart issued by the Royal Horticultural Society of London.


  • Corolla: Average 43 min in diameter at anthesis.
  • Petals: 14 x 20 min.
  • Color: Solferino Purple (Plate 26/ 1) in the bud, fading to Solferino Purple (Plate 26/3) to white in open flowers.
  • Season: Late, along with 'Rome Beauty.'


  • Shape: Short-conic to round to slightly oblate, regular and slightly ribbed in cross section, slightly variable.
  • Size: Averages 70 to 76 mm in diameter: length: width ratio is 0.8 1.
  • Color: Undercolor is Chartreuse Green 663/1 to Indian Yellow (Plant 6/2) fading to Yellow Ochre (Plate o7/2)-, blushed overcolor, 60% to 90% Currant Red (Plate 822/2 to 822/3); pattern is slightly speckled to washed.
  • Skin: Smooth, very slight wax, with inconspicuous tan to slightly russeted round lenticels; little tendency for russet, but occasional scarf skin, medium thick but moderately tough; semi-glossy, somewhat dull.
  • Stem: Average length of 28 to 33 mm. moderately thin.
  • Cavity: Acute to obtuse, medium to shallow depth, medium width, smooth to russeted surface.
  • Basin: Medium depth, medium breadth, rounded sides, smooth to wavy surface, and glabrous.
  • Calyx: Persistent, open, lobes separated at base, narrowly lanceolate, acuminate, recurved.
  • Calyx tube: Conical to funnel-shaped; occasionally open to core cavity.
  • Stamens: Basal.
  • Core-lines: Clasping.
  • Core: Distant, open, medium.
  • Carpels: Round, emarginate to micronate cordate to round, ridged.
  • Seeds: Full complement, acute, non-tufted.
  • Flesh:

    • Texture: Medium coarse-grained, firm, very crisp and breaking; maintains breaking texture in storage.
    • Quality: Delicately spicy, full flavored, fruity, sweet, subacid; very good, improves to best after 1 or more months in storage.
    • Color: Buttercup Yellow (Plate 5/3).
    • Maturity season: One week before 'Delicious.
    • Keeping quality: Improves in storage and retains quality and texture at least 7 months at 1°C.
    • Use: Dessert apple, appropriate for medium and long-term storage.


  • Vigor: Moderate.
  • Shape: Spreading, round-topped.
  • Bearing habit: Some tendency for tip bearing but also bears on short shoots; develops bourse buds, tendency for more than one fruit per cluster; bearing limbs droop under fruit load; fruits hang well on the tree even when overripe; slight tendency for biennial bearing.
  • Branch angle: 45° to 90°.
  • Pruning/training requirements: Renewal pruning is required because of tendency for bare wood on base of branches. The requirements are similar to those of 'Rome Beauty.'
  • Productivity: Heavy, with overbearing possible.
  • Thinning: Requires thinning to keep from overbearing; cluster should be thinned to king fruit.
  • Bark type and color: Current growth Maroon 1030 on distal portion. Basal portion to Willow Green 000862.
  • Stem: Current-year stems are very pubescent; few lenticels, moderately conspicuous, rough, white; lenticels on 2-year-old stems are larger, round, raised, tan, up to 1.6 mm; lenticels on 3-year-old wood are elongated transversely, up to 1.6 x 8 mm; lenticels on older stems are the same color as on bark, raised, corky, 6 x 9.5 mm and orange-tan.


  • Shape: Broadly ovate on new growth, ovate on older growth, compoundly serrate, occasionally simple serrate.


Budwood is available for test purposes to federal and state experiment stations from Purdue Univ., Rutgers Univ., and the Univ. of Illinois. The Purdue Research Foundation has applied for a plant patent under the name 'Co-op 25'. Trees are currently available for sale from the Rocky Mountain Orchard & Nursery Co., New Salisbury, Ind., and will be available from licensed nurseries under the name Scarlet O'HaraTM, which is a trademark of the Purdue Research Foundation.

Literature Cited

  • Crosby, J.A., J. Janick, P.C. Pecknold, S.S. Korban, P.A. O'Connor, S. Ries, J. Goffreda, and A. Voordeckers. 1992. Breeding apples for scab resistance: 1945-1990. Fruit Var. J. 46:145-166.
  • Williams, E.B., J. Janick, F.H. Emerson, S.S. Korban, D.F. Dayton, S.A. Mehlenbacher, L.F. Hough, and C.H. Bailey. 1994. Co-op 23, 24, 25, and 26: Four scab-resistant apple selections released for advanced testing. Purdue Univ. Agr. Expt. Sta. Bul. 456.
  • Zielinski, Q.B. 1955. Modern systematic pomology. Brown, Dubuque, Iowa.

About PRI

Co-op Summary Table

Brief Description

Co-op Release Description

Cultivar Release Description