With the demand for high quality fruit by consumers, the strong pressure to reduce chemical use in agricultural systems, and a need to enhance the economic efficiency of production, tree-fruit growers must look to economically and environmentally sustainable management production systems.
Growers who want to stay profitable must establish high-density plantings with smaller trees using new cultivars. These high-density plantings cost 10 to 20 times more per land area to establish than lower-density plantings, thus greatly enhancing economic risk. Potential returns of high-density plantings, however, far exceed those of low-density plantings, particularly during the first 10 years.
The central component of a high-density system is the rootstock, the part of the tree which provides control of final tree height allowing for closer tree spacing and greater number of trees per land area. The rootstock influences many factors in addition to tree size, particularly productivity, fruit quality, pest resistance, and ultimately profitability.
However, size-controlling rootstocks have not been tested in Alabama conditions. New tree fruit rootstocks cannot be recommended unless there is research investigating soil and climatic adaptability, root anchorage, size control, precocity, productivity, and pest resistance. Additionally, site selection and cultivar choices may be altered to sustainably fit changing climate conditions.
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While the majority of apple cultivars have relatively high chilling requirements, ‘Aztec Fuji’ has a high fruit quality and relatively low chill requirements, which makes it better adapted to maintain productivity in the variable changing climate in the southeast.
A high density apple rootstock study was established at the Chilton Research and Extension Center near Clanton, Alabama in 2014 (Fig. 1) aiming to evaluate the effects of 14 newly developed size-controlling (dwarf) and fire blight resistant rootstocks on apple fruit tree characteristics grown in Alabama environment and to assess the performance and fruit quality of low-chill ‘Aztec Fuji’ cultivar as to enhance the sustainability of fruit growing.
Rootstocks studied include newly released cultivars from Geneva and Vineland rootstock series: B.10, G.11, G.202, G.214, G.30, G.41, G.935, G.969, M.26 EMLA, M.9 T337, V.1, V.5, V.6, and V.7.
Trees are trained to the highly efficient Tall Spindle training system that has not been tested in Alabama before. Tall Spindle is designed to control the vegetative vigor and optimize the crop production especially in the early stage of tree establishment, while providing early returns to the grower.
Evaluations for survival, precocity, productivity, size control, anchorage, suckering, adaptability, and production efficiency are being conducted. Our third year results suggest ‘Aztec Fuji’ trees grafted on Vineland series of rootstocks (V.1, V.5, V.6, and V.7) had the highest number of flower clusters and were the most vigorously growing trees.
Among Geneva series of rootstocks, G. 30 was the most vigorous based on trunk cross sectional area. Trees on G. 969 produced the highest yield of 33.6 lb/tree in 2017 (Fig. 2). Cumulative yield (2015-2017) was high for trees grafted on G.969, V.7, V.6 and G.935 (43, 39.4, 36.7, and 34.6 lb/tree respectively). Trees on G. 969, G.935, and G. 202 also had high yield efficiency.
Trees on V.7 produced the largest fruit size of 182 g, while trees on G.202 had the highest sugar content. The most vigorously growing rootstocks also produced higher number of suckers. Our preliminary results are promising and research is going to continue to assess the production efficiency and fruit quality as a way to achieve more efficient land use and sustainable apple production.