Regulating crop load of ‘Sweetheart’ and ‘Van’ sweet cherry for optimal quality and reduced risk of cracking

Abstract

Sweet cherry is a high value crop where quality attracts a significant premium. Key quality attributes are size, firmness, colour and sugar content as well as lack of physical defects such as cracking, pitting or bruising. The objective of this study was to investigate the impacts of crop load and timing of crop load regulation on 'Van' and 'Sweetheart' fruit quality. In the 2010/11 season trees on F12-1 rootstocks trained to the KGB system were thinned to 1, 2 or 4 buds spur-1 at pre-bloom, full bloom (FB), 2, 4 or 6 weeks after full bloom (WAFB). Fruit diameter was significantly lower in the 4 buds spur-1 treatment (around 26-28 mm) relative to other treatments (around 28-31 mm) in 'Van' at all thinning times with the earliest thinning treatments being the most effective. In contrast, 'Sweetheart' fruit diameter was only significantly lower in the 4 buds spur-1 treatment (26-27 mm) relative to other treatments (27.5-29 mm) at the later thinning times of 6 and 8 WAFB. Fruit soluble solids generally mirrored these trends. Flesh firmness was higher in lower crop loads in 'Van' and was consistent with time after FB. In 'Sweetheart' firmness was higher in the 1 bud spur-1 treatment only and decreased when thinning occurred 6 and 8 WAFB. Exocarp colour was unaffected by crop load or timing of thinning. Incidence of rain-induced fruit cracking was inversely proportional to crop load being around 60, 40 and 20-30% in the 1, 2 and 4 buds spur-1 treatments, respectively. Crop load targets for optimal fruit yield-quality relationships appear to be around 20 t ha-1, though this will carry a greater risk of fruit cracking than higher crop loads.