Contents lists available at ScienceDirect Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti Effects of plant biostimulants on fruit set, growth, yield and fruit quality attributes of ‘Orange rubis®’ apricot (Prunus armeniaca L.) cultivar in two consecutive years Annalisa Tarantino, Francesco Lops, Grazia Disciglio, Giuseppe Lopriore ⁎ Department of Science of Agriculture, Food and Environment, University of Foggia, 71122, Foggia, Italy ARTICLE INFO Keywords: Organic fertilizers Humic and fulvic acids Polyglucosamine Carboxylic acids Blossoming Antioxidant activity ABSTRACT Apricot (Prunus armeniaca L.) is a species particularly prone to erratic production and this behavior has been related to the narrow adaptability of this species. Plant biostimulants are known as organic substances that could enhance growth, development, tolerance to abiotic stresses and crop quality. In this study the effect of three commercial biostimulant products (Hendophyt®, Ergostim®, and Radicon®), compared with control, on fruit set, yield and physical-chemical traits of Orange rubis® apricot cultivar were studied. The investigation was con- ducted during 2015 and 2016 seasons in a commercial orchard in Cerignola (Foggia district, Apulia region, Southern Italy – 41° 15′ 49″ N; 15° 53′ 59″ E; a.s.l 126 m). Foliar treatments with biostimulants were applied at three times (at red ball, fruit setting and fruit development stages) during each growth season. Other than vegeto-productive behavior, as well as blossoming, fruit set and yield, physical, chemical and phytochemicals parameters (total polyphenols content and antioxidant activity) were evaluated. Fruit set percentage, pro- ductivity and qualitative attributes were affected mainly by seasonal growths. Significantly interaction between years and biostimulant applications were noted. All biostimulant treatments gave higher values of antioxidant activity respect to the control. 1. Introduction The apricot tree (Prunus armeniaca L.) is one of the most important fruit species grown in the world, as the fruit is highly appreciated by consumers. Italy is the world’s largest apricot producing country both fresh and dried, which surface is around 18.700 ha and the production about 244,000 tons, mostly located in the regions of Campania, Emilia Romagna, Basilicata and Apulia (ISTAT, 2015). The production data reveals that the Apulia region (Southern Italy) is excellent for heavy production and has seen considerable increase in surface planted with apricot. From 2006 to 2015 there was an increase in surface area of about 95%, passing from 574 to 1120 ha (Mennone, 2016). The fast increasing interest for this crop was also dictated by the transition from a production destined mainly for the processing in- dustry to a destined for the fresh market. This has created the need to satisfy the demands of the consumer, which has considerably appre- ciated the new genotypes, as ‘Orange rubis’ cultivar. Research is hearing conducted all over the world to optimized yield and high – quality apricots. Yield of the apricot tree depends on a number of factors, such as density of flower buds and flowers, fruit size, winter and late springer freeze damages, precipitation amount and orchard management. Most apricot cultivars are characterized by high productivity potential. Abundance of flowering and fruit set are generally much higher than necessary to obtain optimum yield. To achieve satisfactory size and quality of fruit, it is necessary to regulate the crop load using orchard management practices, of which the most important are pruning and fruit thinning. The variability and uncertainty among years of yields is one of the main problems in apricot varieties productivity which is often erratic, depending of several and frequently unclear factors. One of this is the early bloom, which makes the apricot more susceptible than other species to late frosts. The failure in bud development, inadequate bud production and high flower bud drop, consequently have a negative influence on fruit production and yield repeatedly reported in different cultivars and growing conditions (Polat and Caliskan, 2014). Climatic events prior or during flowering are considered as the main determi- nant for apricot fruiting success (Egea, 1995). The apricot fruit trees flower buds differentiate the previous summer, enter dormancy during the winter and resume growth prior to flower the next spring. The https://doi.org/10.1016/j.scienta.2018.04.055 Received 14 February 2018; Received in revised form 24 April 2018; Accepted 25 April 2018 ⁎ Corresponding author at: Department of Science of Agriculture, Food and Environment, University of Foggia, Via Napoli 25, 71122, Foggia, Italy. E-mail address: giuseppe.lopriore@unifg.it (G. Lopriore). Scientia Horticulturae 239 (2018) 26–34 0304-4238/ © 2018 Elsevier B.V. All rights reserved. T