Heat requeriment for inducing budbreaking in different apple cultivars

Abstract

The heat requirements for bud burst of six apple cultivars were evaluated. Shoots with 20 to 25cm
length were submitted to 1,150 cold units. After this treatment, shoots were divided in single bud cuttings and treated at different temperatures (5, 10, 15, 20 and 25oC). The mean time of budbreak (MTB), development index, base temperature and degree-days for budbreak for each cultivar was calculated. The increase of temperature after chilling reduced the MTB in all cultivars. The base temperature to calculate the degree-days varied among cultivars, but has not relation with chilling requirement. The development index improves with temperature increase. The heat requirement is stable at temperatures between 10 and 25oC. The heat requirement is independent of the chilling requirement.