Young apple tree responses to crop load
Biennial bearing is a common and important issue facing apple growers that can result in losses in production of up to 30%, depending on cultivar. To study this issue, a collaborative project focusing on molecular, biochemical and whole tree physiological responses to variable crop loads was established between German research institutions and Agriculture Victoria, Australia. The whole tree physiological component of the project was performed in the Yarra Valley in Victoria, Australia. In spring 2015, a series of crop loads, ranging from almost no fruit on the trees to double normal grower practice, were applied to the biennial bearing cultivar Nicoter (Kanzi®) and to the non-biennial bearing cultivar Rosy Glow (Pink Lady®). Trees were three years old, grafted on M9 EMLA rootstock and trained as Open Tatura. Several tree growth (shoot length and winter wood pruning) and productivity (fruit maturity, size, soluble solids concentration and firmness, and return bloom) factors were measured to understand the effect of crop load. Strength of the response varied depending on the cultivar and factor investigated. In general, all the measured characteristics responded to crop load with the trend inversely proportional to the number of fruit remaining on the trees. Particularly interesting was the return bloom that showed a stronger response in the non-biennial bearing Cripps Pink cultivar than the biennial bearing Nicoter. This could imply that the response of young trees to thinning may be more important than the inherent tendency of the cultivar to biennial bearing.
Stefanelli, D., Plozza, T., Flachowsky, H. and Wünsche, J.N. (2018). Young apple tree responses to crop load. Acta Hortic. 1229, 221-228
'Nicoter', 'Rosy Glow', biennial bearing, return bloom, maturity, fruit quality, IAD index