Studies on Water Transport through the Sweet Cherry Fruit Surface: XII. Variation in Cuticle Properties among Cultivars

Abstract

The cuticular membrane (CM) represents the primary barrier to water uptake into sweet cherry (Prunus avium L.) fruit and thus has a central role in rain-induced cracking. The objective was to quantify CM properties potentially relevant to cracking and to estimate variance components and broad-sense heritabilities for these traits in selected sweet cherry cultivars. Within the scion cultivars, CM mass per area ranged from 0.85 g·m−2 in ‘Rainier’ to 1.61 g·m−2 in ‘Kordia’. Wax mass accounted for one-fourth of CM mass and ranged from 0.21 g·m−2 in ‘Burlat’ to 0.42 g·m−2 in ‘Zeppelin’. Biaxial elastic strain of the CM averaged 76.7% across cultivars and ranged from 56.6% in ‘Namosa’ to 97.0% in ‘Oktavia’. Strain was a linear function of fruit mass (r2 = 0.33, P < 0.0001). Partitioning total variance into variance components revealed that fruit mass, CM, and wax mass and strain of the CM had a high genotypic variance and a low residual error variance. Stomatal density ranged from 0.12 stomata/mm2 in ‘Adriana’ to 2.13 stomata/mm2 in ‘Namosa’. The heritability of stomatal density was 67.5%. Across cultivars and years, mean densities of microcracks were of similar orders of magnitude as those of stomata, but ranges were larger and the heritabilities of microcrack density lower. Permeability for transpiration was lowest in ‘Flamingo Srim’ and highest in ‘Nadino’; that for osmotic water uptake was lowest in ‘Adriana’ and highest in ‘Hedelfinger’. Heritability estimates for permeabilities were low. Based on these data, breeding strategies for less cracking susceptible fruit should focus on genotypes that maintain an intact CM throughout development. This may be achieved by selecting for low CM strain and high CM thickness because thicker CM have more “reserve” for thinning. Finally, genotypes that deposit cutin and wax also during Stage III would be most interesting but were not found among the cultivars investigated.