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), proline, 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 “Nic 29” at each sampling time in 2015 and 2016. However, trees on “Nic 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.
Highlights
World overpopulation mandates the efficient use of natural resources, including water and land
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)
Summary
World overpopulation mandates the efficient use of natural resources, including water and land. Establishment of high-density apple (Malus domestica Borkh) orchards, using new designs on dwarfing rootstocks have become popular in many progressive apple-producing regions around the globe In apples, these new systems typically result in improved fruit quality and yield and rootstocks can influence several postharvest attributes, such as ripening, color, shape and fruit size [1] [2] [3] [4] [5]. Clements reported that performance of “McIntosh” and “Honeycrisp” apples on “Bud 9”, “M.26” and “MM.106” rootstocks, with a central leader (CL), vertical axis (VA), or tall spindle (TS) tree architectures In both cultivars, trees on “Bud 9” had the highest cumulative yield over 2008-2010 (during 3rd through 5th leaf), followed by those on “M.26” and “MM.106” rootstocks. Their studies found that trees trained to TS had the highest production per hectare, followed by those with VA and CL [9]
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