DELAYED COLOR BREAK IN 'TARDIVO', A LATE RIPENING MANDARIN MUTANT, IS RELATED TO A DEFECTIVE ETHYLENE RESPONSE

Abstract

Delaying peel senescence in clementine mandarins is of paramount importance in the citrus industry because it extends the harvesting period and improves the shelf life of the fruits. Gibberellins and ethylene treatments have been used for delaying or accelerating color development in citrus fruit peel, respectively, indicating a prominent role of these hormones in the regulation of the external ripening process. Late ripening mutants constitute an extremely useful tool to decipher the molecular bases regulating the timing and the rate of color development in citrus fruits. Although the causes for these phenotypes may be diverse, there is recent evidence in the literature linking delayed degreening with altered ethylene sensitivity. ‘Tardivo’ is a late ripening mutant of clementine mandarin that displays a delay in peel degreening, color development and expression of carotenoids biosynthetic genes. In the present work we have explored if this phenotype is associated with altered sensitivity to ethylene. Therefore, we have examined the expression of genes involved in carotenoids, ABA biosynthesis, and ethylene signaling and biosynthetic pathways in response to ethylene. The results indicated that ‘Tardivo’ fruits displayed a transient response to ethylene but it was unable to sustain subsequent ethylene-induced gene expression. It is then concluded that the delay in color development of ‘Tardivo’ mandarin may be related to a defective sensitivity or response to ethylene.