Foliar Applications of Urea and a Potent Growth Regulator Ameliorate Calyx-end Cracking in Persimmon

Abstract

Persimmon (Diospyros kaki 'Fuyu') trees were sprayed with 10 mg.L-1 of CPPU [N-(2-chloro-4-pyridyl)-N'-phenylurea] or 1% urea at blooming to determine whether application of these substances would reduce the incidence of calyx-end cracking. Calyx-end cracking decreased with the application of both CPPU and urea. Changes in physiological parameters (length, weight, and height of calyxes, number of seeds, fruit firmness, and soluble solids content) were investigated in response to CPPU and urea. The length and width of the calyx were greatest in CPPU-treated fruits, and the width of the long or short side of the fruit was greatest in urea-treated fruits. Additionally, phytohormones (indole-3-acetic acid, IAA; gibberellic acid, GA(3); zeatin; 2-cis-trans-abscisic acid, ABA; jasmonic acid, JA; and salicylic acid, SA) were analyzed to elucidate the relationship between fruit enlargement and calyx development. CPPU significantly increased levels of GA3 and IAA, while ABA levels decreased in the calyx in all treatments. No significant changes were seen in JA or SA levels. Finally, analysis of anatomical structure showed that CPPU and urea are important in maintaining fruit firmness. Our combined physiological, phytohormonal, and anatomical analysis revealed that CPPU and urea both ameliorate calyx-end cracking in persimmons, and suggests that CPPU and urea may be used to reduce physiological injury in persimmon fruits.