Fruit Quality Attributes of New Peach and Nectarine Varieties under Selection in the Ebro Valley Conditions (Spain)

A breeding program searching for new peach and nectarine varieties adapted to the Ebro Valley growing conditions is being developed at the Aula Dei Experimental Station (CSIC). This program evaluates 15 populations obtained by controlled crosses. Different agronomic parameters such as blooming date, yield, and ripening date were determined in these populations. Quality traits such as fruit type, weight, flesh firmness, soluble solids content (SSC), total phenolics content, antioxidant activity, and other chemical attributes were determined and evaluated. In addition, market life was tested based on chilling injury (CI) susceptibility. Several parameters studied such as yield, SSC, sugars composition, total phenolics, and CI sensibility showed a great variability within the different populations. INTRODUCTION Peach is the most important fruit tree species in the world after apple, in terms of annual production (FAOSTAT, 2005). Moreover, peach is the most dynamic species with respect to the appearance of new cultivars in the market (Byrne, 2003; Fideghelli et al., 1998). The long history of peach breeding explains the great diversification of varieties. This situation has produced a large number of available varieties. Spain is the fourth country in the world in terms of annual yield of peach and nectarine, after China, Italy, and USA (MAPA, 2006). In Spain, the main production areas, located in the Ebro Valley, are Aragón and Cataluña, followed by Murcia. The lack of experimentation with the new varieties in the fruit growing areas means that the advantages of the new varieties have not been fully explored (Carbó and Iglesias, 2002). On the other hand, European producers shipping within Europe may require three to four weeks of storage. Therefore, understanding and preventing the causes of chilling injury (CI) in peaches and nectarines is of economic, as well as scientific, interest. The peach and nectarine consumption per capita remains invariable or decreases in most of the European countries. Consumers complain about lack of flavor, problems with the texture, etc. This situation leads to the need of searching for new varieties with high fruit quality that are best adapted to the growing area (Badenes et al., 1999; Jiang et al., 2002). The main goal of this program is to obtain midor late-season varieties with highmedium chilling requirements, good fruit characteristics and best postharvest behaviour (Cantín et al., 2006a, b; Moreno, 2005). Also, a big diversity in fruit type and market availability period is required by international consumer tendencies. MATERIAL AND METHODS Fifteen controlled crosses were made during 2000 and 2001 in collaboration with Agromillora Catalana S.A. Progenies were established during 2001 and 2002 in an experimental orchard at the Experimental Station of Aula Dei. Since 2004, agronomic and fruit quality traits have been evaluated in this material. Flowering time according to Fleckinger (1945), annual yield, and harvesting time were determined in each progeny. 493 Proc. XII th Eucarpia Symp. on Fruit Breeding and Genetics Eds.: R. Socias i Company et al. Acta Hort. 814, ISHS 2009 When the fruit was ripened, yield (kg/tree) was measured and a representative fruit sample was taken for the quality evaluations. Some pomological traits such as fruit type (peach or nectarine, yellow or white flesh), fruit shape, skin blush, or flesh firmness were also scored. The SSC of the juice was measured with a temperature compensated refractometer (model ATC-1, Atago Co., Tokyo, Japan) and the TA (titratable acidity) was measured by titration with NaOH 0.1 N to pH 8.1. Total soluble phenolic content of methanolic extracts was assayed as described by Cevallos-Casals and Cisneros-Zevallos (2003). Total phenolics were expressed as mg gallic acid equivalent (GA)/100 g fresh weight, based on a standard curve. Antioxidant capacity was adapted from Brand-Williams et al. (1995) using 2,2-diphenyl-1picrylhydrazyl (DPPH) and methanolic extracts, as described by Cevallos-Casals and Cisneros-Zevallos (2003). Change in absorbance at 515 nm was used and results were expressed as trolox equivalents from a standard curve. Chilling injury sensibility was evaluated after cold storage at 5oC according to Crisosto et al. (1999). After two and four weeks of cold storage, a group of ten fruits from each seedling was ripened (at 20°C) until firmness reached between 10-18 N. Fruit was then evaluated for different manifestations of CI such as lack of juiciness (flesh mealiness), flesh browning, and flesh bleeding. Observations were made on the mesocarp and the area around the pit immediately after the fruit was cut transversally to the plane of the suture. Fruit that had a dry appearance and little or no juice after hand squeezing were considered mealy. Fruit was also informally tasted for a feeling of graininess and/or “off flavors” to corroborate visual mealiness assessment. RESULTS AND DISCUSSION Flowering and Harvesting Dates To evaluate flowering date, the average date for each one of the flowering stages was calculated in every progeny. The average harvesting date was also calculated for each progeny (data not shown). Although flowering and harvest time varied every year depending on the annual temperatures and other factors, we observed that the number of days between flowering and harvest time remained stable for each cross through the three years of this study (Fig. 1). This result confirms that flowering time can be used as estimation for harvesting time. The genetic background of the progeny influences the time needed by the fruit to ripen. It is worth saying that flowering date was recorded earlier every year with respect to the previous one, which may reflect the effect of global warming in the plant schedule. Fruit Weight and Yield Regarding annual yield, we have found significant differences among the studied populations (Table 1), and among the progenies belonging to the same cross. This result confirms the effect of the genetic background on the fruit yield and allows selecting the most interesting progenies in terms of production. On the other hand, we have not found any correlation between annual yield and fruit weight, as has been previously reported (Giorgi et al., 2005). In our case, this is probably due to annual fruit thinning. SSC and TA Regarding sugar solids content, significant differences have been found between the different crosses (Table 1). All the genotypes showed values over 10-11o Brix, which is considered the minimum value for consumer acceptance for yellow flesh peaches and nectarines (Crisosto and Crisosto, 2005; Hilaire, 2003; Kader, 1994). However, the relationship between SSC and consumer acceptance is cultivar specific, and there is not a single reliable SSC that assures a given percentage of satisfied consumers (Crisosto and Crisosto, 2005). The highest value (~19 oBrix) was recorded by ‘Venus’ x ‘Big Top’