Producing super-sweet peaches and nectarines under sub-tropical climates

摘要

New systems are being developed to produce super-sweet peaches and nectarines under subtropical conditions of Australia. Most low-chill stone fruit, because of their short fruit development period, exhibit low sugar concentration (9-10° Brix). Slightly higher concentrations (11-13° Brix) can be produced in northern Thailand under drier growing conditions. A minimum acceptable consumer standard for sugar concentration in stone fruit would be 11° Brix, depending on the sugar: acid balance. Stone fruit studies on fruit fly exclusion netting as an environmentally friendly means of preventing fruit fly damage and other insect pest damage provided additional benefits. It changed the microclimate inside the enclosure, resulting in fruit with Brix concentrations as high as 15°. Other management techniques also increase fruit sugar concentrations by an additional 10-20%. Applying foliar growth retardants of pro-hexiodione-Ca (Regalis) or paclobutrazol during early fruit development restricted shoot extension growth; and applying ethylene inhibitors such as AVG 1 week before first harvest delayed fruit maturity and extended the period for carbohydrate accumulation and conversion to sugar. New studies being initiated to produce super-sweet fruit include: micro-climatic modification techniques (exclusion netting), reflective mulches, new training and trellising systems to increase light interception and the best management practices (described above). These systems and practices will be imposed on new, high sugar-accumulating varieties bred at the Maroochy Research Station. These varieties alone, without special practices, can exhibit on average 17° Brix. However, to be able to guarantee that 100% of the fruit reach a minimum standard of 15° Brix, a totally new management system will need to be developed. Other technologies to assess sugar concentration of the fruit after harvest, using near infra-red spectroscopy (NIR) are also being evaluated and will eventually be used in grading and sorting of the fruit so as to deliver to consumers a consistently high-quality product.