ASHS 2025 Conference

Calcium (Ca) is an important macronutrient for plant health and fruit quality. Insufficient Ca in fruit tissues can lead to physiological disorders that reduce crop quality. To prevent this, Ca fertilizers are frequently applied to soil or plant canopies to increase Ca concentrations in fruits. However, the role of Ca fertilizers in promoting fruit quality and overall yields is poorly understood in raspberry (Rubus idaeus). The objective of this study was to evaluate methods to increase Ca concentrations in raspberry fruits and leaves and assess impacts on yield and fruit quality. Replicated field trials were conducted in 2023 and 2024 using floricane-fruiting raspberry ‘WakeHaven’ ‘Meeker’, and ‘Kulshan’ in Whatcom County, Washington. Treatments included: 1) soil application of Ca fertilizer (gypsum) applied before budbreak, 2) foliar application of Ca fertilizer (calcium hydroxide) applied weekly during immature green to white fruit stage, and 3) an untreated control with no calcium fertilizer. Neither method of Ca application affected yield, fruit quality, soil Ca levels, or Ca concentrations within primocane leaves and raspberry fruits across cultivars. However, in ripe fruit, the concentration of Ca in the receptacles was more than ten times higher than in the drupelets of each cultivar. Cultivars with higher fruit Ca concentration also had higher Ca concentrations in the receptacle (Adjusted R2 = 0.58). These findings demonstrate the important role of cultivar genetics when it comes to explaining variations in fruit Ca concentrations. Moreover, results from this study show that standard fertilizer practices have no impact on fruit Ca concentrations or other important yield and fruit quality variables. A physiological barrier limiting Ca movement from receptacles to fruits was identified, and future studies should further explore what these barriers are, when they develop, and whether they can be adjusted to increase Ca transport to raspberry fruits.