Crease: another Ca deficiency-related fruit disorder?

The importance of mineral nutrition (Ca, K and Mg) on the incidence of crease in oranges was investigated by, analysis of fruit sampled from the field, a nutrient shadehouse pot trial of young citrus trees and a Ca spray experiment. Navel orange and Valencia orange fruit were collected from different sites in southwestern New South Wales, Australia. The sites differed in their frequencies and severities of crease. Fruit were sampled based on the presence or absence of crease and fruit tissues were analysed for K, Ca and Mg. In general, concentrations of Ca in rind, albedo and flavedo tissue were negatively correlated with the incidence of crease. The correlation was not so strong for the flavedo compared with the albedo or rind. Pulp Ca concentrations were also negatively correlated, and K/Ca and Mg/Ca ratios were positively correlated with the incidence of crease. Across seven rootstocks, albedo and pulp K/Ca and Mg/Ca ratios tended to show a positive correlation with the incidence of crease in Bellamy navel oranges. In the nutrient shadehouse trial, ten-fold changes in the external K and Ca concentrations produced one to three-fold changes in pulp and albedo K and Ca concentrations of young Leng navel orange trees. Potassium and Ca changes in leaves were less well buffered than that of fruits. A putative relationship between low rind Ca and crease is proposed.