Cambium manipulation, rootstock, and tree architecture influence on phytopigments, proline, chlorophyll index, yield and leaf nitrogen in ‘Fuji’ apple

Abstract

World overpopulation, scarcity of water and finite arable land mandate a more efficient use of these natural resources. To remain sustainable, modern-day apple (Malus domestica Borkh.) fruit production utilizes high-density orchards on semi-dwarfing, precocious rootstocks. Nonetheless, little attention has been paid to the use of size-controlling practices such as trunk girdling in these modern orchard systems. The impact of two rootstocks, two tree architecture (training) systems, and three levels of girdling (in spring) on chlorophyll index (CI), praline, chlorophyll content (Chl; a, b, a + b), carotenoids, anthocyanin, yield, fruit weight and leaf nitrogen (N) in "Aztec Fuji" were studied in 2015 and 2016. Trees on "Bud 9" had up to 5% higher chlorophyll indices in leaves on side branches than those on "Nie 29" at each sampling time in 2015 and 2016. However, trees on "Nie 29" had up to 5.5% chlorophyll index in terminal branches, 14% higher Chl b, 54% higher leaf proline in 2015, up to 5% higher leaf nitrogen (N) in 2015 and 2016, 82% higher yields in 2015, and up to 7% higher fruit weight in 2015 and 2016 than those on "Bud 9". Trees trained into a central leader (CL) architecture had up to 6% higher chlorophyll index and 4% higher leaf N in terminal branches 2015 and 2016, 43% more terminal leaf proline content in 2015, but 13% less yield in 2016 than those with a tall spindle training (TS). Terminal leaves from trees receiving a bark girdling in 2015 (BG15) had up to 6.5% lower leaf N, 7% less chlorophyll index, and between 27% to 56% lower proline content than those from the ungirdled check and score girdled treatment in 2015 (SG15). Also, trees with BG15 and a bark girdling in both 2015 and 2016 (BG1516) treatments had significantly less leaf N concentration than all other treatments or the ungirdled check. Trees that were score girdled in 2015 and repeat score girdled in 2016 (SG1516) had 21 % higher yield and 12% higher fruit weight than those that were ungirdled.