Creasing studies in citrus

[摘要] ENGLISH ABSTRACT: Creasing, also known as albedo breakdown, is a preharvest disorder that affects the albedo ofcitrus fruit causing creases on the surface of the fruit. It is a recurrent problem in Navel andValencia oranges and can cause individual orchard losses which often exceed 50%. Although thecontributing factors are known, the physiological basis of creasing development is unresolved andthe current control measures do not prevent creasing satisfactory. Hence, better control measuresand further understanding of the physiology of creasing development is required.The objective of this two-year study was to determine if the position of fruit in a tree, light andcarbohydrate manipulation techniques, and albedo mineral nutrients influence creasingdevelopment. Furthermore, the most effective application timing of gibberellic acid (GA3) withthe least negative effect on fruit rind colour development and the effectiveness of cytokinins,other products and different root biostimulants to reduce creasing incidence were evaluated.The position of fruit in the tree and light influenced the development of creasing and thedistribution of mineral nutrients in the albedo. Creasing incidence was higher on the south sidethan on the north side of the tree and fruit from the inside sub-sectors had a greater creasingincidence compared to fruit from the outside sub-sectors. The shady part of outside fruit wasmore creased compared to the sunny part of the fruit and covering fruit with brown paper bagsincreased creasing severity. The light manipulation techniques used on the leaves and fruitincreased the nitrogen (N), phosphorus (P), potassium (K) and manganese (Mn) concentrations inthe albedo and differences in the albedo mineral nutrients amongst the sub-sectors evaluated wereobserved, but creasing severity or creasing incidence was not significantly correlated with thealbedo mineral concentrations at harvest. Albedo mineral concentrations earlier in the season mayplay a role in creasing development, as creasing severity was significantly correlated with copper (Cu), K, and Mn concentrations in the albedo during stage II of fruit development. Creasingincidence and albedo mineral concentrations were not affected by any of the carbohydratemanipulation techniques used in this study.The incidence and severity of creasing was significantly reduced, with a minor negative effect onfruit rind colour development, by the application of GA3, from mid November to mid January.Localised fruit application of CPPU [N-(2-chloro-4-pyridyl)-N-phenylurea], MaxCel (6-Benzyladenine) and CPPU in combination with calcium after physiological fruit drop reduced theincidence and severity of creasing, although creasing incidence was not significantly differentfrom the control. The application of Messenger®, AVG (aminoethoxyvinylglycine) and differentroot biostimulants did not reduce creasing incidence. The results showed that cytokinins couldreduce creasing incidence and justify further studies on application and uptake efficiency. Theuse of different root biostimulants are not recommended, but it is suggested that treatment effectsmay be more pronounced over a longer period.

[发布机构] Stellenbosch University