Carolyn Frost
The fruit and flower industries are a major earner of foreign exchange for South Africa, and an obvious potential export growth area. Creating the pre- and post-harvest technology to keep South African products competitive in the demanding overseas market is the focus of a University of Stellenbosch programme, headed by Professor Karen Theron.
The Technology and Human Resources for Industry Programme has given a substantial award to Theron’s team at the department of horticultural science. Not only does it look at improving local horticultural products, but also provides the information and input to ensure the transfer of skills to as many postgraduate students as possible.
The growing of citrus and deciduous fruits and fynbos in the Western Cape is under Theron’s microscope. Research includes industry-related issues like production methods, yield a hectare, quality of fruit, size, shape and colour, harvesting times, storage, shelf-life and transportation to market.
Consumers of fruit are fussy, demanding high aesthetic standards in their fruit. For example, a ton of pears not manifesting the characteristic bi-colour expected of the fruit can drop in value from R3 000 to R300. However, Theron says there is a shift in consumer perception. Although visual impact of fruit is still paramount, the demands for flavour have increased significantly.
But the flavour of fruit is a delicate thing, no matter how delicious the fruit may be when freshly picked from the tree. So harvest and storage conditions have to be tailored to individual cultivars as well as different fruits. An example is the Forelle pear being studied by Dr Deirdre Holcroft. If stored at -0,5C the usual storage temperature for fruit such as apples, pears and peaches Forelle pears become mealy tasting. If stored at 4C they retain their flavour.
This type of research into the differences, in terms of harvest date and maturity upon ripening for different cultivars, answers questions about optimal production. It also raises fresh challenges.
Apple farmers in the Western Cape do not have ideal growing conditions for their products. The winters are too mild and therefore growers have to manipulate the dormancy period of fruit trees to ensure maximum quality and yield. This can be quite a challenge, especially when growers have to adapt to the consistently warmer temperatures of the past few years. Theron’s group is looking at a range of methods to counteract seasonal effects, such as warm winters and hot summers. To counteract the latter problem of trees and fruit overheating, Dr Stephanie Wand has been investigating the adoption of overhead evaporative sprinkler systems. The use of infra-red thermometers has shown that fruit in direct sunlight can register a temperature 15C higher than the ambient temperature. This results in sunburn, lack of colour development and, as trees are under stress, a reduction in fruit size.
Theron’s department is also attempting to improve the way proteas and fynbos are grown, harvested and transported. There is a thriving market for fynbos internationally, but these hardy plants have some vexing problems for commercial growers.
One of the most pressing is of leaves blackening when the flower has been picked. The flower head still produces nectar when it opens in the vase, drawing its carbohydrates from the leaves and depleting them. This complex biological process can be counteracted by “girdling” or ringing the bark below each inflorescence. But this is a labour-intensive process, so other mechanisms to resolve the problem are being investigated. Recently a significant breakthrough was made by Professor Gerard Jacobs in utilising glucose in the vase water.
Controlling the growing season of proteas is also an issue because of the demands of the European market. The natural flowering season is in June and July, but the best window for marketing them is from September to March, corresponding with the European winter when flowers fetch a substantially higher price.
But hopefully with continued research and collaboration, South African flowers will become as important for generating cash as they are for the beauty of the country.