Winter chill models in a mild subtropical area and effects of constant 6℃ chilling on peach budbreak

摘要

Although the Richardson unit (RU) is widely used as a measure of chill units in South Africa, Erez's dynamic model portions (DMP) have given better estimates of winter chilling in areas with warmer winters in Cape Province. At Pietermaritzburg therewere negative RU totals in some winters because of the high daytime temperatures. By adding up RU totals on days when they were positive, an aggregate total gave an estimate of chilling which followed the same trend as DMP. Totals of 11-16 DMP and 150-225 RU were suitable for low chill peach cultivars grown in the area. Container-grown trees exposed to constant 6℃ produced earlier vegetative budbreak than floral budbreak, resulting in reduced fruit set due to competitive sinks. Paclobutrazol drenchesreduced the competitive effect of early vegetative growth.