Causal factors of "Kohansho" disorder in 'Kiyomi' tangor fruit

Abstract

The causes of the occurrence of "Kohansho", a physiological disorder of 'Kiyomi' tangor ['Miyagawa wase' ( Citrus unshiu Marc.) x 'Trovita' orange (Citrus sinensis Osbeck)] fruit were investigated to establish effective preventive measures. The disorder appeared mainly on the fruit surface exposed to sunlight that was over 10°C warmer than the shaded side which was slightly affected. On a clear day, the transpiration rate of sun-exposed fruit was three-fold faster and at night it was only 25% as rapid as that of shaded fruit. Hence, greater water loss of sun-exposed parts is closely associated with the disorder. No significant differences were found in the mineral contents between the sun-exposed and shaded parts, although starch and total sugars were slightly higher in the flavedo of sun-exposed parts. The affected parts had a little greater a* value and more carotenoids than had the normal rind. Shaded fruit had an uneven surface under which the oil-glands protruded, whereas sun-exposed surface had smooth part between round shaped oil-glands.