Figures (1)  Tables (2)

    • Figure 1. 

      The molecular control of seasonal bud development. As days get shorter after the start of astronomical summer, axial buds develop and potentially differentiate. A number of genes shape bud identity during dormancy in autumn, and growth arrests until adequate chill hours are sensed (endodormancy). Following adequate exposure to chill, heat units accumulate (ecodormancy) to activate pathways associated with budbreak. Lesions in any of the complex nodes of these integrated processes may affect dormancy and/or budbreak. Inset photo credits: Darren Turpin (orchardnotes.com)

    • GenotypeOriginParental linesSusceptibilitiesEstimated chilling hours
      'Anna'Israel'Red Hadassiya' × 'Golden Delicious'U250–300
      'Beverly Hills'USA'Melba' × 'Early McIntosh'F, PM300
      'Big River'USAUnknownU250–400
      'Dorsett Golden'BahamasSeedlingU250–300
      'Ein Shemer'Israel'Zabidani' × 'Golden Delicious'U200–300
      'Elsa Sweet'USAUnknownU200–300
      'HRMN-99'IndiaSeedlingU*Unknown
      'Julieta'Brazil'Anna' × 'Mollie's Delicious'U300–450
      'Joy's Apple'USAUnknownU200–300
      'Lady Williams'Australia'Rokewood' × 'Granny Smith'PM, S200–300
      'Pettingill'USASeedlingU300
      'Shell of Alabama'USASeedling
      		U200-400
      'Tropical Beauty'South AfricaSeedling
      		U100
      'Tropic Sweet'USA'NJ38' × 'Anna'S300–400
      'Vered'Israel'Calville St. Sauveur' × unnamed local seedlingF, S, PM100–200
      'Winter Banana'USASeedlingCAR, S300–400
      Winter Cox'USAUnknownU250–300
      CAR, cedar apple rust; F, fire blight; PM, powdery mildew; S, scab; U, unknown; * While the estimated chilling hour range is unknown, the cultivar has been successfully grown in low-chill areas of the country (500 chilling hours or fewer).

      Table 1. 

      Varieties described as 'ultra-low chill' (300 chilling hours minimum or fewer).

    • Apple namePlace of originApple originsSusceptibilitiesEstimate range of chilling hours
      'Caricia'Brazil'Anna' × 'Prima'U350–450
      'Chenango Strawberry'USASeedlingF400
      'Cripps Pink'Australia'Golden Delicious' × 'Lady Williams'CAR, F, PM, S400–500
      'Cripps Red'Australia'Golden Delicious' × 'Lady Williams'F, PM, S400–500
      'Cauley'USASeedlingF400–500
      'Eva'Brazil'Anna' × 'Gala'U330–350
      'Fuji'Japan'Red Delicious' × 'Ralls Janet'CAR, F400–500
      'Gala'New Zealand'Kidd's Orange Red' × 'Golden Delicious'C, CAR, F, PM, S400–500
      'Gordon'USASeedlingU400
      'Granny Smith'AustraliaSeedlingF, PM, S400–500
      'Hawaii'USA'Golden Delicious' × 'Gravenstein'S*Unknown
      'Maayan'Israel('Calville St. Sauveur' × 'Damascus') × 'Delicious'U450
      'Michal'Israel('Calville St. Sauveur' × 'Damascus') × 'Delicious'U425
      'Mollie's Delicious'USA('Golden Delicious' × 'Edgewood') × ('Red Gravenstein' × 'Close')C450–500
      'Princesa'Brazil'NJ56' × 'Anna'U350–450
      'Red Astrachan'RussiaSeedlingC, S*Unknown
      'Reverend Morgan'USASeedlingU*Unknown
      'San Jacinto'USASeedlingU*Unknown
      'Summer Champion'USASeedlingCAR, S*Unknown
      'White Winter Pearmain'USASeedling
      		S400
      C, canker; CAR, cedar apple rust; F, fire blight; PM, powdery mildew; S, scab; U, unknown; * While the estimated chilling hour range is unknown, the cultivar has been successfully grown in low-chill areas of the country (500 chilling hours or fewer).

      Table 2. 

      Apples reported to break dormancy in response to 300–500 chilling hours.