Effects of new rest-breaking chemicals on flowering, shoot production and yield of subtropical tree crops

Chilling, or the alleviation of drought, is required to cause the transition of both vegetative and floral buds of temperate or semi-deciduous subtropical fruit species from the dormant to active state. The chilling requirement of the variety must closely match the amount of chilling received at the location otherwise the variety will exhibit signs of lack of chilling such as sporadic budbreak and uneven shoot development along branches. Several experiments were conducted in south-east Queensland to determine whether various combinations of new rest-breaking chemicals could induce more uniform budbreak and increase flowering of a range of low-chill temperate and subtropical species (low-chill stonefruit, persimmon and custard apple). These experiments demonstrated the beneficial effects of using rest-breaking chemicals to break dormancy, advance flowering and fruit maturity, and increase lateral number by reducing strong apical dominance. The most successful rest-breaking chemicals were Armobreak^® and Waiken^® but only when combined with potassium nitrate which greatly improved their efficacy by 20-30%. Compared with Dormex^®, these combinations appear to have relatively low mammalian- and phyto-toxicity increasing their potential for safe commercial use. Further testing on a wider range of species/varieties and environments are needed to determine the optimum concentrations and timing.