Suboptimal Winter Chilling Impedes Development of Acrotony in Apple Shoots

摘要: In 1997, 1-year-old, unbranched, ≈1-m-long shoots of the apple (Malus ×domestica Borkh.) rootstock 'Merton-Immune 793' (MI.793) were selected at random from two commercial stoolbeds in Western Cape, South Africa, during dormant period. One site has mild winters (307 Utah Chill Units (CU) 34 °S, 300 m) while other is moderately cold (1497 CU 33°S, 950 m). 1998, 'Granny Smith' collected a mature orchard another warm area (574 34°S, 116 Shoots prepared and forced 25 °C with continuous illumination. During dormancy developmental rate was determined terminal bud, both distally proximally situated lateral buds, or without inhibitory influence distal disbudded shoot piece (10 cm long). area, growth bud increased shortly before spring budburst such that weak acrotonic tendency established. The shorter period, as experienced common to apple-growing regions impeded full development acrotony subsequent apical control. With less chilling (mild areas) basitonic remained. Budburst slower more erratic, inhibition by parts accentuated. Delayed foliation may be due correlative than endodormancy. When buds are released paradormancy they exhibit potential similar to, or, chilling, even greater than, bud. This permits expression autonomy between shoots.