Quantifying the Effects of Chelated Calcium and Salicylic Acid on the Postharvest Quality of Poinsettia Cuttings

Vegetatively propagated unrooted cuttings typically are grown in equatorial locations and shipped via airfreight to propagators located in temperate climates. Cutting quality, defined as the resistance to external forces, such as physical damage and pathogen infection, impacts postharvest durability during shipping and propagation. During our previous studies, foliar application of calcium (Ca) in the form of Ca chloride was effective at increasing leaf mechanical strength of poinsettia (Euphorbia pulcherrima) and zonal geranium (Pelargonium ×hortorum). Calcium chloride applied at ≥800 mg·L−1 Ca caused phytotoxicity symptoms in poinsettia; therefore, in the current work, we investigated the use of chelated Ca by providing Ca at 40, 80, or 160 mg·L−1 and salicylic acid (SA) at 150 or 300 mg·L−1 to increase the mechanical strength of poinsettia leaves. Mechanical strength of leaves was assessed using a force-displacement graph generated from a texture analyzer using a ball probe to penetrate a unit area of a clamped leaf. The peak force to fracture the leaf and work-of-penetration, defined as the area under the force-displacement curve, were used as indicators of mechanical strength. Calcium concentration in the leaves increased by 27% with increased application of Ca from 0 to 160 mg·L−1. Peak force was 26% greater in treatments with Ca at 80 or 160 mg·L−1 compared with the untreated control. Work-of-penetration was 24% and 29% greater for treatments with Ca at 80 and 160 mg·L−1, respectively, compared with the control. Foliar application of SA did not affect leaf mechanical strength. Chelated Ca applied at 160 mg·L−1 Ca caused visual phytotoxicity symptoms; thus, applications of 80 mg·L−1 Ca are recommended to improve resistance to physical damage for poinsettia leaves.