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

Cherry fruit cracking is a costly problem for cherry growers. The effect of repeated sprayings (gibberellic acid - GA₃ ; abscisic acid - ABA; salicylic acid - SA; glycine betaine - GB, and Ascophyllum nodosum - AN) combined with CaCl₂ , 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.

All spray treatments reduced cracking compared with an untreated control (H₂ O), with fewer cheek cracks. The least cracking incidence was observed for ABA + CaCl₂ - and GB + CaCl₂ -treated fruits, indicating an added benefit compared to spraying with CaCl₂ alone. In addition, GB + CaCl₂ -treated fruits showed higher fruit diameter. ABA + CaCl₂ and GB + CaCl₂ sprays showed higher wax content and higher cuticle and epidermal thickness compared with the control, including increased expression of wax synthase (ABA + CaCl₂ ) and expansin 1 (GB + CaCl₂ ).

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. © 2020 Society of Chemical Industry.