2019 ASHS Annual Conference

‘Honeycrisp’ is an extremely popular apple, but is susceptible to certain disorders, mainly bitter pit. The impact of different levels of fruit thinning at two stages of fruit growth on yield, fruit quality, and seasonal leaf and fruit mineral nutrients and the influence of five rootstocks on fruit quality at harvest and after storage and fruit quality attributes and final leaf and fruit mineral status were studied over two seasons. Early and late thinning of fruit down to one fruit per spur reduced fruit firmness but increased fruit size, color, and bitter pit compared to the lighter thinning levels in both years. It appeared that early thinning would lead to larger fruit size with less bitter pit than late thinning. Thinning influenced mineral nutrient fluctuations in leaf and fruit. Most of the leaf and fruit mineral concentrations decreased in all thinning treatments as the growing season progressed. Trees on G.30 and V.1 rootstocks had lower firmness in both 2017 and 2018. Trees from G.202 rootstocks tended to have lower yield and smaller fruit size, leading to higher firmness in both 2017 and 2018. 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 one year. The magnetite of fruit Mg in trees on G.969 and G.202 were opposite to their fruit Ca. Analyses of different tissues revealed that fruit skin in the calyx end and wedges had higher Ca and lower K/Ca ratio than did other tissues. There was a significant and strong correlation coefficient between Ca concentrations of calyx end skin plus skin flesh and bitter pit, and thus calyx end could be a preferred tissue for detection of Ca status and bitter pit disorder in ‘Honeycrisp’ apples.