Rapid fruit growth induced by foliar mineral nutrition increases cracking risk in greenhouse grown watermelon (Citrullus lanatus)

Abstract

Abstract Foliar mineral nutrition is widely used to improve crop growth and productivity; however, its physiological effects and associated trade-offs, such as fruit cracking, in watermelon ( Citrullus lanatus ) remain unclear. This study assessed the effects of various foliar mineral formulations on the vegetative growth, photosynthetic performance, fruit development, cracking incidence, and yield of hydroponically grown watermelon under greenhouse conditions in Japan. Four treatments were applied in a completely randomized design: an unsprayed control (T0) and sprayed Ca, Zn and B (T1); micronutrients with Ca (T2) and micronutrients only (T3) prepared based on our previous studies. Foliar treatments affected growth and physiology; T3 increased leaf area (4.7%), stem diameter (4%), plant height (12%), biomass (29%), chlorophyll content (16.3%), and photosystem II efficiency (17.4%) compared to control. Although it accelerated early fruit growth, T3 markedly increased immature fruit cracking, reaching 45.4% compared with only 13.6% in the control treatment. Fruit growth rate showed a significant positive correlation (r=0.70) with cracking incidence, whereas mineral concentrations in the pulp and rind did not differ significantly between cracked and uncracked fruit, indicating that cracking was primarily due to growth dynamics rather than nutrient imbalance. Foliar treatments increased fruit diameter and individual fruit weight, with T2 producing the highest total yield (36.7% increase vs. control). Fruit quality attributes, including soluble solid content, acidity, and juice pH, were not significantly affected by any treatment. Overall, foliar mineral nutrition application enhanced physiological performance and yield potential in watermelon; however, excessive stimulation of early fruit growth increased susceptibility to cracking, highlighting the need for balanced foliar nutrient management strategies.