Project Coordinator:
Dr Graham Barry,

Collaborating researchers and technicians involved:
Dr Graham Barry, Prof. John Bower,
Dr Frikkie Joubert.

The enhancement of fruit quality, both internal and external, including fruit size, is integral to maintaining competitive advantage and increasing market share in our export markets.

(Pruning, Girdling, Fertigation, the Open Hydroponic System, Irrigation, fertilization and testing of new products are covered in this project.)

Featuring:

1. Internal fruit quality

- Total soluble solids (TSS - sugars)

- Acid - maintaining acid levels and reducing acid
  levels of cultivars/ in climatic areas
- Managing juice content of fruit
- Granulation prevention
- Endoxerosis on lemons

A new concept was developed in cooperation with Australian researchers to identify the sites on the tree where high versus low quality fruit are borne. These results allow us to identify the sites where high quality fruit are borne on the tree and to remove branches bearing low quality, small fruit, selectively through pruning.

2. External fruit quality:

- Fruit colour
- Creasing
- Rind texture
- Fruit splitting

The use of ethylene degreening is now being used commercially, after adaptation of Spanish and USA systems to suit South African conditions. Most of this project covers fruit colour improvement and risk management strategies of the degreening process. Some research is being conducted on creasing control.

3. Fruit size manipulation:

- Test and register new Plant growth regulators We have conducted research for the registration of 2,4 dichlorophenoxy propionic acid ("Corasil E") and 3,5,6 trichloro propionic acid ("Maxim") as fruit size enhancing chemicals and have tested the products on all citrus cultivars. The effect of these synthetic auxins is substantial. They thin small fruit and enhance the medium sized fruit, but do not affect the largest fruit at the time of spraying. The result is a very uniform fruit size on the tree with excellent economical returns. Hand thinning norms for oranges do exist for producers wishing to thin fruit.

4. Fruit size prediction model

Various models have been developed to predict aspects of integrated fruit production. A model for predicting fruit and crop size has been developed and is currently being tested semi-commercially. Maturity indexing is used commercially to predict crop maturity and harvesting dates. A model for predicting creasing is being refined. A prediction system for estimating fruit susceptibility to oleocellosis has been completed and is currently used commercially.