2018 ASHS Annual Conference

The use of size-controlling rootstocks and crop load adjustment are routine practices in the high-density apple orchards. The influence of five thinning levels and five rootstocks on yield, fruit quality, and mineral fluctuations in leaf and fruit tissues were studied in ‘Honey Crisp’ apple. Both early and late thinning of fruit down to one fruit per spur reduced fruit firmness but increased fruit size, and color compared to the lighter thinning levels. Trees receiving early thinning had less bitter pit than those with late fruit thinning. Thinning influenced mineral nutrient fluctuations in leaf and fruit. Trees on G.30 and V.1 rootstocks had larger fruits with lower firmness in 2016. Fruit from trees on G.202 had higher firmness in both 2016 and 2017. Fruit from trees on G.30 were largest in 2016 but smaller in 2017. Trees with G.30 had higher but those on G.202 had lower yield per tree than those on other rootstocks in 2016. Trees on M.26 EMLA had higher but those on G.202 had lower leaf N, Mg, Mn and fruit N, leading to better color in the scion fruit with G.202 in 2016. Trees on G.969 and G.202 had higher but those on G.30 and V.1 had lower fruit Ca in 2016. Trees on G.969 also had high leaf Ca in 2016. The magnetite of fruit Mg in trees on G.969 and G.202 were opposite to their fruit Ca. Although year-to-year yield variations may lead in to different results in some fruit attributes and mineral concentrations, some obvious consistent rootstock effects were observed in both years. For successful production of high quality ‘Honey Crisp’ apple, the combined impact of rootstock and thinning on tree growth, yield, fruit quality and mineral nutrient concentrations should be considered, and we are closer to achieve this combination in our study.