Artificial spur extinction to regulate crop load and fruit quality of 'Kalei' apple

Abstract

'Kalei' is a new scab-resistant apple cultivar released by the Department of Agriculture, Fisheries and Forestry, Queensland. It is a large apple (average weight 200 g) and trees are highly productive. Crop load management is important as overthinning and/or under-thinning can reduce yield and fruit quality. Artificial Spur Extinction (ASE) is a crop load management tool to regulate floral bud type and density just prior to the onset of spring budbreak. The impact of ASE on the productivity and quality of 'Kalei' was studied across three seasons at Applethorpe, Queensland, with trees on MM.106 and M.26 rootstocks trained as a Vertical Axis (2500 trees ha-1). ASE was compared with conventional (Conv) crop load management (no bud removal, and hand thinning seven to eight weeks after full bloom). In the ASE treatments, axillary buds borne on one-year old shoots were removed, whilst spur buds, and terminal buds of one-year old shoots (≥2.5 cm) were set to a predetermined bud density. ASE increased the proportion of terminal buds borne on shoots, compared with Conv management. ASE consistently improved fruit set, with fewer flower buds failing to set fruit and a higher proportion of flower buds setting 2 or 3 fruit. In 2012 and 2013, the mean fruit weight of 'Kalei' apples was greater with ASE than Conv management. By removing competing sinks early in the season using ASE, remaining fruitlets are given the space and resources to attain fruit size potential. No increase in yield was observed with ASE in both seasons. ASE increased 'Kalei' red blush coverage in 2013, but had no impact on flesh firmness, total soluble solids or dry matter content in 2012 or 2013.