Effects of exogenous compound sprays on cherry cracking: skin properties and gene expression

BACKGROUND Cherry fruit cracking is a costly problem for cherry growers. The effect of repeated sprayings (gibberellic acid – GA 3 ; abscisic acid – ABA; salicylic acid – SA; glycine betaine – GB, and Ascophyllum nodosum – AN) combined with CaCl 2 , on ‘Sweetheart’ cherry fruit‐cracking characteristics was investigated. Cracking was quantified in terms of cracking incidence, crack morphology, confocal scanning laser microscopy, cuticular wax content, cell‐wall modification, and cuticular wax gene expression. RESULTS All spray treatments reduced cracking compared with an untreated control (H 2 O), with fewer cheek cracks. The least cracking incidence was observed for ABA + CaCl 2 ‐ and GB + CaCl 2 ‐treated fruits, indicating an added benefit compared to spraying with CaCl 2 alone. In addition, GB + CaCl 2 ‐treated fruits showed higher fruit diameter. ABA + CaCl 2 and GB + CaCl 2 sprays showed higher wax content and higher cuticle and epidermal thickness compared with the control, including increased expression of wax synthase (ABA + CaCl 2 ) and expansin 1 (GB + CaCl 2 ). CONCLUSION In general, factors that improve the cuticle thickness appear to be important at the fruit‐coloring stage. At the fruit‐ripening stage, larger cell sizes of the epidermis, hypodermis, and parenchyma cells lower cracking incidence, indicating the importance of flexibility and elasticity of the epidermis.