1. Chilling injury of citrus fruit

Chilling injury (CI) is especially relevant to South Africa, as fruit is shipped at -0.5 Celsius for insect sterilization purposes. CI manifest in the flavedo in various forms i.e., pitting, sunken areas on fruit, scalding/browning and glassy looking fruit that appears as though it has been frozen.
This ongoing project aims to test current postharvest handling protocols, such as forced air cooling and wax application, to decrease the incidence of CI. However, the project is also focused on improvement of the rind condition during fruit development, as well as decreasing fruit susceptibility to CI by new postharvest manipulations with various agrochemicals and fluctuations in temperature and gaseous conditions.

2. Rind breakdown and pitting of various citrus fruit

Paul Cronje (CRI)

Rind breakdown is one of the postharvest physiological disorders related to the collapse of the oil glands. The symptom, a dark randomly distributed pitting of the flavedo, normally develops during shipment of the fruit. In this project the aim of the research is to understand firstly the pre harvest conditions i.e. influence of canopy position on within tree mineral nutrient and carbohydrate allocation which determine the rind condition and sensitivity to rind breakdown. The second objective is to develop optimum postharvest handling protocols to reduce the incidence of this physiological rind disorder.

3. Peteca spot on lemons

Paul Cronje and Keith Lesar (CRI)

Peteca spot of lemons, characterized by random, darkened depressions or sunken areas in the rind, can occur as early as 3-5 days after harvest. The project is currently focused on understanding the impact of postharvest treatments viz. harvesting, general handling of fruit, degreening, waxing and storage. Information from these experiments is used to determine handling protocols to manage and reduce the risk of peteca spot development.

4. Studies on citrus creasing (albedo breakdown)

Dr Stephan Verreynne (CRI at US)

Creasing or albedo breakdown is a physiological disorder resulting in separation of adjacent cells in albedo tissue giving the peel a creased appearance. In South Africa it was first observed in 1938 and is a major problem in the Eastern and Western Cape, especially with Navels and Valencia's. Previous research has dealt with the control of creasing in relation to application of calcium sprays and application of gibberellic acid (GA3). However, little or no work has been done to establish an effective GA3 application timing without the negative colour effect, the relationship between the bearing position of the fruit and creasing incidence, the effect of girdling, light manipulation and improving root activity on the incidence of creasing. The aim of these studies is to evaluate these factors in relation to creasing incidence in Navels to better understand the mechanism of creasing development in order to control it.