Leaves of the tree.

The leaves of the cultivar Myrto have the following dimensions: length 10.7 cm, width 6.3 cm, length of leaf petiole 4.8 cm, and thickness of leaf petiole 2 mm. On MM 106 rootstock, this cultivar is moderately vigorous and has excellent productivity that is stable from year to year. However, its performance has not been tested on other rootstocks. The anthesis of the cultivar Myrto occurs between 16 and 22 Apr., whereas the anthesis of the cultivars Golden Delicious and Granny Smith occurs 12 to 20 and 13 to 18 Apr., respectively. Unopened flowers of the cultivar Myrto are medium pink in full balloon stage, whereas at full bloom, the petals are mainly white with a slight medium pink blush. The productivity of ‘Myrto’ is not significantly different from ‘Golden Delicious’, but it is higher than ‘Granny Smith’ (Table 1). ‘Myrto’ trees are as susceptible to apple scab [Venturia inaequalis (Cke.) Wint.] and powdery mildew [Podosphaera leucotricha (Ell. & Ev.) Salm] as its parents (Syrgianidis, 2004). However, more research is needed so its resistance to other diseases can be evaluated.

Table 1.

Productivity, fruit weight, fruit firmness, fruit length/width, and total soluble solids of the cultivars Golden Delicious, Granny Smith, and Myrto over a period of 4 years.

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Fruits.

Fruit characteristics reported in Tables 1 and 2 are mean values taken over 4 consecutive years from 2004 to 2007. The experimental layout was a randomized complete block design including six replications of the three cultivars, including five trees per replication. The differences between means were evaluated by using the Duncan's multiple range test at P ≤ 0.05.

Table 2.

Total sugars, pH of juice, ascorbic acid, L-malic acid, Thiault index, and total titratable acidity of the cultivars Golden Delicious, Granny Smith, and Myrto over a period of 4 years.

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Fruits of the cultivar Myrto have a light green skin color and are oblong conical with the following dimensions: length 8.5 cm, width 8 cm, pedicel length 2.5 cm, pedicel thickness 1.5 mm (Table 1; Fig. 1). Length/width of ‘Myrto’ fruits is not significantly different from ‘Golden Delicious’, but it is higher than ‘Granny Smith’ (Table 1). The width and depth of the calyx cavity of the cultivar Myrto is 1.75 cm and 0.6 mm, respectively. Fruits are covered by a light waxy layer and have an average number of small, inconspicuous lenticels. The lenticels are white with halos like ‘Granny Smith’. This variety is not subject to sunburn. For the climatic conditions of northern Greece, fruits ripen late (20 to 25 Oct.), whereas harvest dates for the cultivars Golden Delicious and Granny Smith are 8 to 14 Sept. and 19 to 25 Oct., respectively. Fruit weight of ‘Myrto’ is not significantly different from that of ‘Golden Delicious’, but it is higher than ‘Granny Smith’ (Table 1). Larger fruit size is one advantage of ‘Myrto’ over the also late-maturing cultivar Granny Smith. ‘Myrto’ trees have a very low percentage of preharvest fruit drop (1.2%), expressed as a percentage of a total number of fruits per tree. Thinning is necessary so that the trees can set annually heavy crops and to avoid biennial bearing. Bearing happens mainly on spurs but also on 1–year-old shoots. Two pickings are required. An important characteristic of ‘Myrto’ is that its fruits do not show symptoms of epidermal russeting. However, the fruits of the cultivar Golden Delicious showed some symptoms of epidermal russeting during some years. The fruit flesh of the cultivar Myrto is creamy white, aromatic, very crisp, and juicy. Flesh of fruits does not brown soon after being cut. The fruits have a tart flavor. Fruit firmness (kg·cm⁻²) measured with an Effegi penetrometer 11-mm tip (Effegi Model FT 327; Alfonsine, Italy) of the cultivar Myrto at harvest is high, higher than ‘Granny Smith’ and similar to ‘Golden Delicious’ (Table 1). The total soluble solids (%) measured with an Atago PR-1 electronic refractometer (Atago Co Ltd., Tokyo, Japan) of ‘Myrto’ were not significantly different from ‘Golden Delicious’ but were higher than those of ‘Granny Smith’ (Table 1). The total sugars (as described by Koukourikou-Petridou et al., 2007) of the cultivars Myrto and Golden Delicious were higher than those of ‘Granny Smith’, whereas the pH of juice was not different for the three cultivars (Table 2). The ascorbic acid content (vitamin C; mg/100 g fresh weight) measured by oxalic acid 1%; Koukourikou-Petridou et al., 2007) of the cultivar Golden Delicious was higher than that of ‘Granny Smith’. L-malic acid (g·L⁻¹) and the total titratable acidity (%) measured as described by Koukourikou-Petridou et al. (2007) were decreased in the following order: ‘Granny Smith’ > ‘Myrto’ > ‘Golden Delicious’ (Table 2). The Thiault index (total sugars plus 10-fold of malic acid) of the cultivars Myrto and Granny Smith were higher than those of ‘Golden Delicious’ (Table 2). Thiault index is used to characterize apple fruit quality at harvest (optimum value for the cultivar Golden Delicious is 180) as well as fruit storability during cold storage (Thiault, 1971). Some years fruits showed the physiological disorder “bitter pit,” but this problem was resolved by calcium sprays (Syrgianidis, 2004). The fruit maintains firmness, juiciness, and flavor very well in standard cold storage (0 to 1 °C) for ≈6 months (Syrgianidis, 2004).

Fruits of the cultivar Myrto.

Citation: HortScience horts 44, 5; 10.21273/HORTSCI.44.5.1452

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Fruits of the cultivar Myrto.

Citation: HortScience horts 44, 5; 10.21273/HORTSCI.44.5.1452

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Fruits of the cultivar Myrto.

Citation: HortScience horts 44, 5; 10.21273/HORTSCI.44.5.1452

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In conclusion, ‘Myrto’ seems to be a promising apple cultivar that may eventually replace ‘Granny Smith’ as the late-maturing green apple of choice for commercial production.