Abstract
The effect of tree growth-control technologies on apple tree vegetative development, productivity and fruit quality was investigated with apple cultivar ‘Rubin’ on dwarf rootstock P 60 at the Institute of Horticulture, Lithuanian Research Centre for Agriculture and Forestry in 2015–2018. Eight treatments were established combining tree trunk incision by chainsaw before flowering, application of prohexadione-calcium in different dose and time, summer pruning in August and root pruning before flowering. Root pruning from both sides of the tree significantly reduced tree trunk diameter, shoot length and pruning weights but at the same time reduced fruit weight. It increased tree productivity and enhanced fruit colouring. Two applications of prohexadione-calcium significantly reduced mean shoot length and increased average fruit weight. Summer pruning had a positive impact on fruit colouring. Trunk incisions enhanced leaf P, K and Fe content. Pro-Ca increased leaf Ca content. Trees root pruned from both sides had one of the lowest contents of all tested minerals. All tree growth-control technologies had a positive impact on tree productivity , fruit quality and bearing stability comparing with control treatment.
Highlights
Regulation of tree vegetative growth in intensive orchards is one the most important tasks for fruit growers
In our study all applied growth-control treatments significantly reduced total shoot length and average shoot length compared with the control treatment (Table 1)
Pro-Ca reduces terminal growth by inhibiting the synthesis of gibberellins that are responsible for regulation of terminal growth in apple trees, which is the most pronounced in treetops
Summary
Regulation of tree vegetative growth in intensive orchards is one the most important tasks for fruit growers. To optimize the growth and yield of apple trees, different dwarfing rootstocks are usually chosen depending on the vigour of a particular apple cultivar. Under Lithuanian climatic conditions, trees of medium- or stronggrowing apple cultivars are too vigorous even on the dwarf rootstocks (Kviklys et al 2013). Other technological means are required to optimize apple tree growth. Growth regulator prohexadione-calcium (Pro-Ca) and root pruning are widespread tree growth-reduction technologies (Ferree et al 1992, Rufato et al 2017). Trunk incision effectively restricts tree growth and it was used mainly for the strong-growing trees (Hoying and Robinson 1992)
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