Journal of Applied Botany and Food Quality 88, 259 - 263 (2015), DOI:10.5073/JABFQ.2015.088.038 Fruit Research Institute, Eğirdir, Isparta, Turkey Reduction of apple vegetative shoot growth cv. Starcrimson Delicious/MM 111 with prohexadione calcium application does not decrease fruit quality M. Çetinbaş * , S. Butar, A. Atasay, M. İşçi, H. Koçal (Received June 29, 2015) * Corresponding author Summary Prohexadione-calcium % 10 (Pro-Ca) has been shown to effectively reduce the vigor of apple trees. However, it is important that the reduction of vegetative shoot growth does not decrease yield and fruit quality. The primary objective of this study was to determine the response of Starcrimson Delicious/MM111 apple trees to foliar Pro-Ca application and its effect on vegetative growth and fruit quality. For this reason, trees were sprayed twice within a three weeks interval with 62.5, 125, 250 g/100 L water Pro-Ca when annual shoots reached 5 cm. Pro-Ca applications decreased the growth of annual shoots and shoot length of apple trees. Shoot length was decreased by 31 % for shoots treated with P-Ca. The number of nodes and average internode length were signifcantly reduced for P-Ca-treated shoots, conferring a higher node density relative to control shoots. Three weeks intervals of application Pro-Ca applied shoot 125 and 250 g/100 L water dosage is more effective in terms of reducing the development. Fruits from Pro-Ca treated trees did not signifcantly differ in size or other observed quality characteristics (frmness, soluble solids content (SSC), titratable acidity (TA), and fruit color) from fruits from the control group. As a result, application Pro-Ca of 125 g/100 L dosages for Starcrimson/MM111 apple varieties can be recommended. Introduction World production of apples (Malus domestica Borkh) is close to 81 million tonnes, with a surface area under cultivation of 5.2 million ha. Production in Turkey is about 3.3 million tonnes, distributed over 173 thousand ha (FAO, 2013). A high percentage of orchards are situated on semi-vigorous or semi-dwarf rootstocks. Some 70 % of the plants produced in nurseries in Turkey are on MM 106 (48 %) or more vigorous rootstocks (22 %). Approximately 4 % of the apple seedling production in Turkey constitutes the Starcrimson Delicious apple (BUGEM, 2014). Starcrimson Delicious/MM 111 gardens are mostly found in the Isparta-Eğirdir region. The ‘Starcrimson Delicious’ is an important apple in Eğirdir and is a high yield and fruit and favor quality apple. However, the use of tall trees results in lower labor effciency (harvest, pruning, and thinning), and a higher use of agro-chemicals per hectare. For this reason, it is important that reduction of this apple tree’s vegetative shoot growth does not decrease the yield and fruit quality. Plant height reduction is playing an important role in promoting both yield and quality, and in decreasing cost, space, and labor (HAYASHI et al., 2001; KARLOVIC et al., 2004). One of the many methods used in the world are various foliar sprays with plant growth retardants for plant height reduction. One such plant growth retardant is Pro-Ca (STEFFENS et al., 1993; KIM et al., 2010; DUYVELSHOFF and CLINE, 2013). Pro-Ca has been found to reduce the growth of various plants such as rice, apples, pomes, petunias, and various vegetables and grain crops (LEE et al., 1998; COSTA et al., 2004; ILIAS and RAJAPAKSE, 2005; ERGUN et al., 2007; KIM et al., 2007). Pro-Ca is a recently developed plant growth retardant used in apple and other fruit trees (GREENE, 1999; ROEMMELT et al., 2003). It was frst used on rice and small grains in Japan and France, and will be introduced for use on apples (Malus × domestica) in the United States and several European countries (YODER et al., 1999; COSTA et al., 2001). Pro-Ca is an acylcyclohexanedione, and acts on the blocking of 3β-hydroxylation (RADEMACHER, 2000) and prevents the biosynthesis of active GA’s. This process is known to happen late in the bio-synthesis pathway of gibberellins (BARCEL, 2005). High rates of gibberellin biosynthesis stimulate excessive vegetative growth. The Inhibitors of the gibberellin biosynthesis retard growth and improve plant productivity and/or performance (RADEMACHER, 1991). Paclobutrazol, a gibberellin biosynthesis inhibitor, was used successfully on fruits trees to control growth and improve fruit quality − although it is not commercially available in the United States for this purpose (GREENE, 1991; 1999). Of this, prohexadione- calcium appears to be particularly effective, and has the potential to improve performance (GREENE, 1999). The purpose of this investigation was to determine the optimum concentrations in the application of prohexadione-calcium 10 % for controlling the vegetative growth of apple trees, as well as the effects of Pro-Ca 10% on fruit quality. In this work, we studied the effect of reducing the plant height on fruit quality, vegetative growth, and labor effciency at harvest, using cv. ‘Starcrimson Delicious’ grafted on semi-vigorous MM 111 rootstocks in the successive two years (from 2013/2014 to 2014/2015). Materials and methods Orchard layout and experimental design The experiments were carried out in the Fruits Research Station in Eğirdir, and Isparta in an orchard located at 37°49’ N latitude and 30°52’ E longitude and 926 m above sea level, the Eğirdir Province in the Mediterranean region of Turkey. To determine the effect of Pro-Ca %10 on vegetative growth control and the fruit quality parameters of apples, uniform 5-years old ‘Starcrimson Delicious’ apple (Malus domestica Borkh) trees grafted on MM 111 rootstocks (spaced 5 × 4 m) were selected and grouped into four blocks with 32 trees in each, based on proximity in the orchard and crop load. The experimental design was a randomized block, with 4 treatments and 4 replicates, using a double tree for each treatment. The trees were trained to a central leader and pruned in winter, and standard cultural practices had been used on the trees for several years. The trees were sprayed twice with 0 (water + surfactant), 62.5, 125, 250 g/100 L water Pro-Ca %10 in the annual shoots 5 cm within a three week interval in the spring (I. and II. years) (Fig. 1a, b). All the spray solutions contained ‘Spur’ as a surfactant [0.01%, v/v (Sumi-Agro, Turkey)]. The pulverized treatments were applied with a low pressure hand sprayer. Assessment of fruit quality and vegetative growth Fruit Quality The fruits were harvested at the commercial stage of maturity. The pro-Ca-treated fruits and untreated fruits were harvested separately