AGRONOMIC AND QUALITY PARAMETERS OF FLAT PEACH UFO3, UFO4 AND SWEETCAP®

Headnote

ABSTRACT

The agronomic and fruit quality characteristics of the peach cultivars 'Ufo3', 'Ufo4' and 'Sweetcap®' cultivars grown in Murcia, Spain are reported. The cultivar 'Sweetcap®' is a mid-season flat peach while Ufo3' and 'Ufo4' are early flat peaches. 'Sweetcap®' displayed good plantation uniformity, had an average yield of 5.1 kg/m^sup 2^, a high calibre fruit and weight (162.5 g), high soluble solids content (12.7°Brix), high pulp yield (97.0%) and high quality taste. The cultivars 'Ufo3' and 'Uf o4' also displayed good plantation uniformity, with a higher average yield than 'Sweeteap®' (5.2 and 5.3 kg/m^sup 2^, respectively), an average fruit weight that was slightly less, 90.6 g for 'Ufo3' and 103.3 g for 'Ufo4', flatter fruit, and a soluble solids content ranging from 11.4° to 12.2°Brix. The 'Ufo4' cultivar had lower acidity and very high-quality tasting fruit (high SSC/TA ratio).

- Key words: flat peach, fruit quality, fruit size, Prunus persicae, total acidity, yield -

INTRODUCTION

Peach [Prunus persicae (L.) Batsch] is the third most important fruit grown in the world, after apples and pears. Peach production comes mainly from China, the Mediterranean area (Italy and Spain) and the United States (FAOSTAT, 2007). In Spain, peach is one of the most important fruit species cultivated and it produces around 26% of the total EU production. Spain is the second largest European producer after Italy (FAOSTAT, 2007). In 2007 the Spanish Murcia region (CARM, 2008), the third most important peach producing region, produced 241,292 tons: 85.5% peaches, 9.5% nectarines and 5.0% flat peaches.

Traditionally, production and marketing of flat peaches in Spain has been limited both in quantity and quality. The main drawbacks of traditional cultivars are their lack of appealing colour, low consistency of the fruit and excessive cracking of the pistil which means the product does not meet market quality demands. In addition the traditional varieties do not sufficiently supply year-round demands. Just over a decade ago new flat peach cultivars, which have more attractively coloured fruit and good consistency, were introduced into Spain and peach production and marketing have increased. The newly introduced flat peach cultivars came mainly from France (Agro Selection Fruits) and Italy (Istituto Sperimentale per la Frutticoltura, Rome), but these countries have not yet experienced the production increase that has occurred in Spain.

In the 1980s, the Istituto Sperimentale per la Frutticoltura in Rome began a breeding program to obtain a cultivar with a higher yield, improved organoleptic quality, better consistency of flesh and increased fruit size and without split pits. All these objectives were set to create a number of cultivars that ripened at different times, so as to avoid an oversupply at any one time. To fulfil these goals, crosses were made using parental genotypes with flat fruit and genotypes with standard or globe-shaped fruit (NICOTRA et al, 2001a,b). The result was a new type of peach, called UFO. The UFO series contains 9 cvs: from 'Ufol' to 'Ufo9'.

In the 1990s, Arsène and Laurence Maillard began a genetic improvement program to obtain new flat peach varieties. The 'Sweetcap®' Maillarflat cultivar and the 'Regalcake®' and 'Nectacake®' series of cultivars were developed and these have been greatly strengthened in recent years with the acquisition of many varieties that virtually cover the whole fruit production calendar, from mid- to late-season.

The basic difference between the cultivars originating in Maillard (France) and those in Italy, is that the cultivars from Maillard are midseason (second half of June) and late-season varieties (mid September), while those originating in Rome are mostly early varieties with some mid-season and one or two late-season varieties. The results of the two programs are complementary in terms of providing new flat peach cultivars that cover a wider harvesting period.

In this study the agronomic behaviour and organoleptic quality parameters were evaluated in two Italian Ufo flat peach cultivars ('Ufo3' and 'Ufo4') and the 'Sweetcap®' cultivar (Maillarflat). The cultivars were all grafted onto the GF-677 hybrid rootstock, widely used for peach. While literature reports numerous studies on the agronomic performance of this rootstock when grafted with different peach cultivars (GIORGI et al, 2005, HUDINA et al, 2006, SPORNBERGER et al, 2005 and ZARROUK et al, 2006). The characterization of morphological, physical or organoleptic properties of the cultivars under assay have not been reported.

MATERIALS AND METHODS

The peach cultivars [Prunus persicae (L.) Batsch] 'Ufo3' and 'Ufo4' (originating from crossing Maybelle x Saturn, of Italian origin) and 'Sweetcap®' (obtained by Maillard of French origin) were studied. All cultivars were grafted onto the hybrid rootstock GF-677 Prunus persicae x Prunus amygdalus).

The trial was conducted at an experimental orchard located near Cieza, Murcia, Spain (Latitude 38° 17'N - Io 27'W). Soil conditions were poor and stony in the first layer (0-10 cm) and clayish below this level (clay loam texture). Soil was highly calcareous with a 15% content of active lime and a pH of 7.8. The 'Ufo3' and 'Ufo4' planting density was 4 x 1.5 m, and that for 'Sweetcap® was 5 × 2.5 m, trained to a central leader system. The study was conducted during the period 2005-2008. Conventional commercial summer pruning and drip irrigation treatments were performed. A randomised block design was used with five single-tree replications for each variety. Guard rows were used to preclude edge effects.

The onset of bud sprouting, full bloom and petal fall were recorded on five trees per variety and on four branches per tree. Branches were homogeneous in all cases with a similar length (30-60 cm), located at three different heights in the tree (low, medium, high) and marked at the phenological stage A (BAGGIOLINI, 1952). Full bloom was recorded when more than 50% of the flowers were open.

The number of fruits/m^sup 2^ and yield (kg/m^sup 2^) were measured. The number of fruits/m^sup 2^ was determined as the ratio between the total number of fruits per tree and the tree spacing. Yield (kg/ m^sup 2^) was determined as the ratio between the total kilograms of fruit per tree and the tree spacing.

Samples of 50 fruits per variety (10 fruits per tree) were hand-harvested at random at the commercial maturity stage, on the basis of their skin colour (fully-coloured). Immediately after harvest, fruits were transported in an airconditioned car to the laboratory. Fresh weight, equatorial, suture and polar diameter, flesh thickness, flesh firmness, stone weight, width and length, pulp yield, pH, soluble solid content (SSC), titratable acidity (TA), SSC/TA ratio and colour were measured. Fruit and stone weight were measured with a Sartorius digital balance (model BL-600, 0.01 g accuracy, Goettingen, Germany). Fruit equatorial, suture and polar diameter and flesh thickness, as well as stone width and length were measured with Mitutoyo electronic digital slide gauge (model CD15DC, 0.01 mm accuracy, England, U.K.). Pulp yield percentage was calculated as (fruit weightstone weight) /fruit weight x 100.

Flesh firmness (FF) was measured with a Bertuzzi Penetrometer (model FT-327, Facchini, Alfonsine, Italy) with an 8-mm cylindrical plunger and measurements were made on the two opposite faces in the equatorial zone. The CIELAB L* (brightness or lightness; 0= black, 100 = white), a* -a* = greenness, +a* = redness) and b* (-b* = blueness, +b* = yellowness) colour variables were measured on the skin on the four opposite faces in the equatorial zone, using a chromatometer (CR-300, Minolta Co., Osaka, Japan).

The chemical analyses were carried out on four juice samples (10 peaches each). The juice was extracted using a blender and filtered through cheesecloth. Juice pH was calculated by a Crison pH-meter (model MicropH 2001, Barcelona, Spain). Soluble solids content (SSC) was measured at 200C with a refractometer (Atago Co., Tokyo, Japan). Titratable acidity (TA) was determined with an acid-base potentiometer (0. IN NaOH up to pH 8. 1) and is expressed as grams per liter (g/L) of malic acid. The ripeness index (RI) was calculated as the ratio of soluble solids content and total acidity.

Statistical analysis

Statistical analyses were performed using SPSS 16,0 for Windows. Abasie descriptive statistical analysis was followed by an analysis of variance test for mean comparisons, with standard errors. To discriminate among the means (multiple range test), the Fisher's least significant difference (LSD) procedure was used at the 95.0% confidence level. Pearson correlation coefficients were determined.

RESULTS AND DISCUSSION

Agronomic parameters

During the three-year study, the onset of bud sprouting in 'Ufo3' and 'Ufo4' cultivars occurred around the first two weeks of February, two weeks ahead of the 'Sweetcap ©'cultivar (late February) (Table 1). 'UfoS' and TJfo4' can be considered early harvest cultivars: (late May-early June). The fruit was harvested in 8-12 days. 'Sweetcap ®' is clearly a mid-season harvest cultivar, (mid July). The fruit was harvested in 152 1 days. Under the tested cultivation conditions, 'Ufo3' was harvested 26 days earlier than 'Big Top' and 21 days earlier than 'Ufo4'.

There was no significant difference in yield among the cultivars studied (mean value 5.2 kg/m^sup 2^). The number of fruits per m2 in cultivars 'Ufo3' and 'Ufo4' were similar (53.6 and 49.2 fruit/m^sup 2^, respectively) and were greater than that of 'Sweetcap ®* (39.5 fruits/m^sup 2^).

Fruit quality parameters

The fresh fruit weight for cultivar 'Ufo3' (90.6 g) was 7.8% greater than that obtained by NICOTRA et al (2001a), while the average fruit weight for cultivar 'Uf o4' (103.4 g) was 9.75% lower than that obtained by NICOTRA et al. (2001a). These differences are probably due to the different environmental conditions. The cultivar 'Sweetcap ®' had the heaviest fruit (162.5 g), probably due to being a later ripening variety compared to the Ufo cultivars tested (Table 2).

'Sweetcap ®' produced the largest but the least flattened fruit (largest polar diameter) compared with the 'Ufo3' and 'Ufo4' cultivars. 'Ufo3' and 'Ufo4' had a greater fruit diameter compared with those obtained by NICOTRA et al (2001b, 2002) but lower than that of 'Sweetcap ®* (Table 2). Flesh thickness was significantly greater for 'Sweetcap ®' (24.9 mm) than for 'Ufo3' and 'Ufo4\ 'Ufo3' had the lowest flesh thickness values.

Fruit from the three cultivars had low-acidity with pH values greater than 4.0 (DIRLEWANGER et al 2006) (Table 3). 'Sweet cap®' had a greater TA compared to 'Ufo3' and 'Ufo4' (Table 3).

The total soluble solids content (Table 3) for the early cultivars 'Ufo3' and 'Ufo4' was 11.4° and 12.2°Brix, respectively; the values were lower than those obtained by NICOTRA et al (2001b). The mid-season cultivar 'Sweetcap ®' had a value of 12.7° Brix, which was not significantly different from cultivar 'Ufo4\ The highest SSC/TA ratio was recorded for the 'Ufo4' cultivar (high quality taste).

Table 4 shows that the 'Ufo3' fruit had lighter, smaller stones (3.2 g), while the 'Sweetcap ®' cultivar produced fruit with larger heavier stones (4.6 g). The highest pulp yield (97%) was recorded for 'Sweetcap®'; despite having the largest stone, the fruit was the largest and heaviest.

Flesh firmness (Table 5) was very similar among the three cultivars, although cultivars 'Sweetcap ®' and 'Ufo3' had the most consistent fruit flesh.

Fruit colour is an important factor for marketability and consumer acceptance and can also be indicative of the ripeness index. Cultivars 'Ufo3' and 'Ufo4' produced the reddest (high a* values) skin, while cultivar 'Sweetcap®' had the yellowest skin (high b* and low a* values) (Table 5). The a*/b* ratio was the lowest for the 'Sweetcap®' cultivar. The Lvalues of fruit of 'Ufo3', 'Ufo4' and 'Sweetcap®' did not differ significantly.

Correlation analyses

The interdependence of the variables was assessed by a correlation analysis in which fortytwo pairs of variables were correlated (Table 6).

Correlation analyses showed that the greatest correlation was between fruit weight and equatorial diameter (r = 0.87), suture diameter (r = 0.79) and polar diameter (r = 0.85), as well as fruit weight and flesh thickness (r =0.61) and fruit weight and stone weight (r = 0.62). The pH was negatively correlated with TA (r = -0.68) and positively correlated with the SSC/TA ratio (r = 0.69), while the TA was negatively correlated with the SSC/TA ratio (r = -0.91).

Skin brightness was negatively correlated with skin redness (a* values) r = -0.70 and a*/b* ratio (r = -0.77). Similar results have been reported for other clingstone peaches (DROGOUDI and TSIPOURIDIS, 2007). Skin redness (a* value) was positively correlated with the a*/b* ratio (r = 0.98), while the skin yellowness was negatively correlated with a*/b* ratio (r = -0.76).

We conclude that the 'Sweetcap ®* cultivar is a good mid-season flat peach due to its potential size, production uniformity and very high-quality taste. Cultivars 'Ufo3' and 'Ufo4' are two good options for early flat peach cultivars for marketing. They may weigh less and be smaller than 'Sweetcap®'. This is compensated by their early harvest because they can get very high prices, since they are the first on the market. The size of cultivars 'Ufo3' and 'Uf o4' improved under our growing conditions (Murcia, Spain), compared to reports by NICOTRA et cd. (2001b). 'Ufo4' was proven to be more regular compared to 'Ufo3\ which was more variable.

Given the remarkable variability in flat peaches, this study must be extended to other cultivars present on the market and to promote those with a high organoleptic, nutritional and nutraceutical profile. The results of this study confirm that these three flat peach cultivars are highly recommended and of interest to the Murcia area and other Mediterranean countries with similar edaphoclimatic conditions.

References

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Revised paper received July 31, 2009 Accepted November 4, 2009