PRINCIPAL INVESTIGATOR: Dr Paul Cronjé
CONTACT DETAILS: +27 21 808 2689/ +27 84 447 1047/ paulcronje@sun.ac.za
DUARTION: One year
PHI-1 CONTRIBUTION: R250000
LEAD INSTITUTIONS: Citrus Research International and Stellenbosch University (Department of Horticultural Science)
BENEFICIARY: The citrus industry
The South African fresh fruit industry has a longstanding reputation for high quality citrus. An evenly coloured rind is distinctive of healthy fruit, but rind disorders cause the blemishes and decay that can lead to market rejection and economic losses. Rind related research is a significant part of Citrus Research International (CRI) studies. However, the actual causes, prevention and treatment of rind disorders remain elusive. To accelerate progress, Spanish experts were invited to collaborate with South African researchers in a citrus rind workshop.
Spanish experts brought to South Africa
In February 2009, Prof. Lorenzo Zacarias and Dr Fernando Alférez from Valencia and Dr Lluis Palou from Ivia participated in a two-day workshop, held in Nelspruit, Mpumalanga. Members of the Citrus Cold Chain Forum (CCCF) study groups attended, representing pack houses in Mpumalanga, Limpopo, KwaZulu-Natal, the Eastern and Western Cape.
Holistic solutions for rind disorders
The Spanish researchers shared their expertise and made recommendations in line with integrated production management practices:
- Dr Palou, a post-harvest pathologist, explained how temperature control, fungicides and GRAS compounds are used in Spanish pack houses to control citrus decay.
- According to Dr Alférez, pre-harvest conditions like sudden changes in temperature and relative humidity can cause rind collapse and subsequent staining and pitting.
- Producers should remove field heat immediately after harvesting to ensure that humidity and temperature remain constant in the time between picking and packing.
- Canopy management by more pruning can ensure that fruit on the inside of the canopy receive the necessary sunlight for photosynthesis and good rind colour development.
- Carbohydrate levels and the balance of water and mineral nutrients determine physiological rind condition. It can be enhanced by more sunlight and the application of mineral nutrient sprays to the foliage.
- Dr Paul Cronjé (CRI) and Prof. Zacarias explained how seasonal temperature variances and the interaction of different genetic environments can predispose certain citrus cultivars to develop chilling injury during cold storage and shipment. Harvesting at optimum maturity and discarding overripe and immature fruit can reduce the risk. The Spanish suggestion of immersing citrus for a few minutes in hot water baths at 50°C is an expensive treatment in South African terms.
Citrus rind workshop leads to continued collaboration
- The citrus rind workshop facilitated technology transfer. Spanish recommendations were distributed to the CCCF pre-season pack house workshops. They were also published in the industry paper, the Cutting Edge.
- However, the most significant outcome of the citrus rind workshop was international collaboration. Mutual information exchange strengthened ties between the two countries and the Spanish contingent gained insight into South African conditions by visiting farms, pack houses and cold stores.
- Since the workshop, Prof. Zacarias and Dr Alférez invited Dr Cronjé to work with them in Valencia. For three months in 2011, they conducted experiments on aspects affecting rind disorders on Valencia and Clementine fruit, which exposed Dr Cronjé to Spanish research methods and indicated shortages in South Africa.
- Collaboration will continue in a new Post-Harvest Innovation Programme project (PHI-2), which will utilise Spanish expertise on gene molecular technology.
