ISHS Acta Horticulturae 632: XXVI International Horticultural Congress: Citrus and Other Subtropical and Tropical Fruit Crops: Issues, Advances and Opportunities
THE PHYSIOLOGICAL CONTROL OF CITRUS CREASING |
| Author: | J.P. Bower |
| Keywords: | Rind disorders, mineral nutrition, pectins, cell walls |
| DOI: | 10.17660/ActaHortic.2004.632.14 |
| Abstract:
Citrus creasing is a disorder characterized by multiple cracking in the albedo, resulting in weak rind. Such fruit is not packed. Various attempts at control of the disorder have been made. In South Africa, gibberellic acid is sprayed in the late summer. However, this only delays creasing development. Calcium sprays have only limited success. Using data orchards in the Eastern Cape region of South Africa, fruit pectin analysis during fruit development, indicated rapid changes in total as well as constituents during the first six weeks post petal fall. Activity of an enzyme, believed to be uronic acid oxidase, correlated with creasing incidence at harvest, if assayed at four to five weeks post petal fall. Simultaneous mineral analysis of fruits explained, through multiple regression, over 90% of variation in pectin gelling, and in turn was successful in predicting creasing. While a number of elements appeared to play a role, the cause of creasing is probably multivariate, with molybdenum being of critical importance. It is suggested that this element acts as a co-factor in ureide synthesis, required in the formation of galacturonic acid, a major component of pectins. Of further importance was sulphur, believed to be a component of uronic acid oxidase. Calcium was found to be of lesser importance. It is suggested that creasing occurs due to a lack of adequate pectin formation and cross-linking. A major cause of this problem may be a lack of ureide formation, although in some orchards other points in the pectin formation pathway may be important. It is suggested that the solution to creasing is through identification of the critical restriction to pectin synthesis at any particular site, and application of the required element or elements. | |
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