agriculture Article Effects of Branch Number on Quality Traits and Yield Properties of European Hazelnut (Corylus avellana L.) Tuba Bak 1 and Turan Karadeniz 2,* 1 Crop and Animal Production Department, Mudurnu Süreyya Astarcı Vocational School, Bolu Abant Izzet˙ Baysal University, Mudurnu, Bolu 14800, Turkey; [email protected] 2 Department of Horticulture, Faculty of Agriculture, Bolu Abant Izzet˙ Baysal University, Bolu 14030, Turkey * Correspondence: [email protected]; Tel.: +90-530-203-88-66 Abstract: Despite being the world leader in the production of hazelnuts, Turkey’s nut yield per hectare is quite behind other producer countries. The main reasons for low yield are the completion of the economic life of hazelnut orchards and the lack of pruning following the technique. Hazelnuts are being grown with the ‘ocak’ system in Turkey. The ocak system is a bush-like growing technique that does not contain the main trunk but consists of shoots instead. It is necessary to maintain the optimum number of shoots per ocak to increase yield and quality in this system. The effects of different branch numbers on yield and fruit quality parameters of ‘Tombul’ and ‘Palaz’ hazelnut cultivars were investigated in Ordu ecological conditions. ‘Palaz’ had the highest yield per ocak in 8 branches (1460.19 g), while ‘Tombul’ had in the 5 branched ocak (2170.47 g). ‘Palaz’ and ‘Tombul’ had the highest fruit weights in 4 and 4–6 branches, respectively. The highest oil ratio of ‘Palaz’ was observed in 4 branches, while ‘Tombul’ had the highest in 5 branches. The highest kernel ratio was determined in 6 and 5 branches in ‘Palaz’ and ‘Tombul’, respectively. The ocaks with 4 and 5 branches Citation: Bak, T.; Karadeniz, T. were mostly expressed higher values, and it is foreseen that the number of branches should not Effects of Branch Number on Quality exceed 6 to reduce the competition of the branches and to obtain good quality products. Traits and Yield Properties of European Hazelnut (Corylus avellana Keywords: hazelnut; branch removal; yield; fruit quality; ‘ocak’ L.). Agriculture 2021, 11, 437. https://doi.org/10.3390/ agriculture11050437 1. Introduction Academic Editors: Kourosh Vahdati, Anita Solar and Neus Aletà Hazelnut is one of the important Turkey-originated fruit species. Turkey has quality cultivars and suitable areas for hazelnut production. The hazelnut growing areas in Turkey ◦ ◦ Received: 18 March 2021 are at 40–41 North and 37–42 East coordinates. The Black Sea coast is the most suitable Accepted: 23 April 2021 area in terms of ecologic conditions for hazelnut cultivation within these limits [1–3]. On the Published: 12 May 2021 Black Sea coast, hazelnut growing areas reach 80 km from the coast and 1300 m altitude [4]. In Turkey, hazelnut is cultivated in 16 provinces, including the oldest grower provinces, Publisher’s Note: MDPI stays neutral Giresun and Ordu. The hazelnut production area reached 706 thousand ha while it was with regard to jurisdictional claims in 650 thousand in 2004 with an increment of 8.17% increase. Turkey constitutes 66% of world published maps and institutional affil- hazelnut production. Ordu province is the leading producer province in Turkey with iations. 217,000 t [5] and provides 27.97% of production by itself [6]. Turkey is dramatically behind the other hazelnut-producing countries in terms of nut yield despite being the leading hazelnut exporting country. It ranks 10th with 64.2 kg·ha−1 yield while the USA has 269 kg·ha−1, France has 221.3 kg·ha−1, and China has 197.9 kg·ha−1 Copyright: © 2021 by the authors. yields. The unpleasantly low yield is due to cultivation with old branches, deficits in tech- Licensee MDPI, Basel, Switzerland. nique, and completion of the economic lives of orchards [6]. This article is an open access article Researchers made efforts to maintain a quality fruit in most of the fruit species. distributed under the terms and Special efforts on hazelnut mainly focused on pollinizers [7], grafting [8], canopy [9], conditions of the Creative Commons fertilization [10,11], planting density [12], and training systems [13]. Climatic conditions, Attribution (CC BY) license (https:// cultivar, and location are some of the other variables that affect hazelnut’s fruit quality creativecommons.org/licenses/by/ and chemical composition [14]. In Turkey, the ‘ocak’ system (Figure1) is used in the 4.0/). Agriculture 2021, 11, 437. https://doi.org/10.3390/agriculture11050437 https://www.mdpi.com/journal/agriculture Agriculture 2021, 11, x FOR PEER REVIEW 2 of 10 Agriculture 2021, 11, 437 2 of 10 chemical composition [14]. In Turkey, the ‘ocak’ system (Figure 1) is used in the cultiva- cultivationtion of hazelnuts of hazelnuts,, and ocaks and ocaks comprise comprise old and old andplenty plenty of branches. of branches. Ocak Ocak is a is bush a bush--like likegrowing growing system system that that consists consists of no of nomain main trunk trunk as a as tree. a tree. Branches Branches are areall con all consideredsidered as a astree a tree without without connecting connecting a trunk. a trunk. Even Even though though this this system system is issuggested suggested for for flatlands flatlands by bymany many researchers researchers [4,15,16] [4,15,16, cultivation], cultivation with with this this system system is being is being used used in all in growing all growing areas areasof Turkey. of Turkey. Pruning Pruning application application is isgenerally generally performed performed as as removingremoving excessivelyexcessively oldold branchesbranches or or newborn newborn suckers suckers and and pruning pruning on on branches branches is is not not performed. performed. In In recent recent years, years, thethe studies studies about about the the ocak ocak system system [ 17[17–19–19]] and and its its effects effects on on yield yield and and quality quality increased increased significantly.significantly However,. However, these these studies studies are are still still insufficient, insufficient and, and there there need need to to be be a a lot lot more more studiesstudies describing describing the the ocak ocak system system and and its its effects. effects. Clarifying Clarifying the the effects effects of of branch branch numbers numbers inin ocak ocak is is one one ofof thethe mostmost crucialcrucial issuesissues among all studies. studies. This This study study was was carried carried out out to todetermine determine the the effect effect of of the the number number of of br branchesanches in ocaksocaks onon fruitfruit qualityquality parameters parameters in in ‘Palaz’‘Palaz’ and and ‘Tombul’ ‘Tombul’ cultivars. cultivars. FigureFigure 1. 1.Ocak Ocak system system with with low low ( a()a) and and high high ( b(b)) branch branch density density (photos (photos were were taken taken by by the the author). author). 2.2. Materials Materials and and Methods Methods 2.1.2.1. Material Material ThisThis study study was was conducted conducted in in a a farmer’s farmer’s orchardorchard during during thethe 2008 2008 and and 2009 2009 seasons. seasons. ‘Palaz’‘Palaz’ and and ‘Tombul,’ ‘Tombul which,’ which are are the the most most cultivated cultivated hazelnut hazelnut cultivars cultivars in Turkey, in Turkey, were used were asused material. as material. The planting The planting age of theage orchardof the orchard was 60. was There 60. was There no was pruning no pruning application applica- on branches.tion on branches. Only sucker Only removalsucker removal had been had performed been performed as a pruning as a pruning application application since since the establishmentthe establishment of the of orchard. the orchard. ‘Palaz’:‘Palaz’: This This hazelnut hazelnut variety, variety, which which has has medium medium taste taste and and quality, quality, is is widely widely grown grown inin Ordu. Ordu. The The fruit fruit is is round round and and flat, flat, the the top top is is wide, wide, and and the the tip tip is is fluffy. fluffy. There There is is a a brown, brown, thinthin integument integument attached attached to to the the flesh flesh on on the the inner inner fruit. fruit. The The fruit fruit is is white white with with a a relatively relatively largelarge kernel kernel cavity. cavity. It canIt can grow grow even even in clayey, in clayey, sandy, sandy, and gravelly and gravelly soils with soils low with soil low depth. soil ‘Palaz’ wakes up relatively earlier than other hazelnut varieties in spring, making it more depth. ‘Palaz’ wakes up relatively earlier than other hazelnut varieties in spring, making sensitive to late spring frost. Çotanaks of this cultivar varies between 2 and 4. Husks are it more sensitive to late spring frost. Ç otanaks of this cultivar varies between 2 and 4. generally 1.5 times the length of the fruits [20]. Husks are generally 1.5 times the length of the fruits [20]. ‘Tombul’: It is considered the most important hazelnut cultivar grown in Turkey. It ‘Tombul’: It is considered the most important hazelnut cultivar grown in Turkey. It is widely grown in Giresun province. The very good fruit quality has made it the most is widely grown in Giresun province. The very good fruit quality has made it the most demanded hazelnut in international markets. Although it tends to periodicity, it gives demanded hazelnut in international markets. Although it tends to periodicity, it gives regular and very high yield every year under good cultivation conditions. Its ripe fruit is regular and very high yield every year under good cultivation conditions. Its ripe fruit is plump and regular. It expands towards the table part, narrows evenly towards the end, plump and regular. It expands towards the table part, narrows evenly towards the end, and ends with a pointed tip.