Phenotypic characteristics of black apricot Prunus × dasycarpa cultivar ‘Shlor-Tsiran’ in Armenia

Sampling and field observations of the black apricot cv. ‘Shlor-Tsiran’ were carried out in Armavir Province of the Republic of Armenia, at the orchard with local apricot cultivars collection of the Echmiadzin Scientific Center of Agriculture and at a fruit plants nursery in the village Lenughi, located in the Ararat Valley semi-desert zone, at an altitude of 800–855 m above the sea level. The climate of the Ararat Valley is sharply continental. During the year, the mean daily temperature ranges from −3°C to 26°C. The average annual temperature is +11°C, the annual precipitation is about 300 mm and the average annual relative air humidity is 59%. Tree planting density in the collection garden is 5 m × 4 m, and the trees are 10-year-old at the time of research. The conditions are favourable for the cultivation of apricot. Samplings and measurements have been performed in triple; in each repetition, samples were collected and measurements were taken from five trees. Sampling and field observations of P. armeniaca and P. cerasifera were carried out in the Yerevan Botanical Garden NAS RA at the ‘Flora and Vegetation of Armenia’ exhibition plot with fruit plants living collection. The climatic indicators in the Ararat Valley are close to those in the Yerevan Botanical Garden located in the zone of stony wormwood semi-desert at an altitude of 1200–1250 m above the sea level. The absolute minimum temperature in the Yerevan Botanical Garden is 2°C–3°C which is lower than that in the Ararat Valley.

Phenotyping of cv. ‘Shlor-Tsiran’ was performed according to UPOV (2016) (Tables 1 and 2). Tree habitus, growth and shoot characteristics, shoot growth dynamics, phenophase changes, leaves, flowers, fruits and harvest counting, depending on the crown formation, was evaluated according to the programme and methodology for studying cultivars of fruit, berry and nut crops (Sedov and Ogoltsova, 1999). Visual and measurement observation types were used. The onset of fruit ripening was assessed on trees in the orchard. The degree of separation of the kernel from the pulp and the volume of the fruit and kernel were evaluated in the laboratory. The kernel bitterness was assessed by tasting. Harvest time is based on changes in fruits shape, flavour and colour. The harvest amount data were analysed statistically using the dispersion analysis method, and the quantitative characteristics of the fruit and leaf were analysed according to qualitative and quantitative change methodology (Khachatryan, 2002; Mamajanyan, 2018).

The measurements were carried out during the beginning of flowering in the end of March. Friable closed flowers were used to determine pollen fertility, from which the pollen was easily shaken off onto a glass slide. Pollen fertility was determined on temporary preparations stained with acetocarmine. On each preparation, 100 pollen grains were counted in three repetitions. The number of fertile (well-coloured) and sterile (not coloured or partially coloured) pollen grains was determined. To determine the germination of pollen grains, large buds were covered with paper bags and placed in a desiccator with silica gel in a refrigerator. Pollen germination was performed using a drop of an aqueous solution of sucrose at a concentration of 20%. The glass slide with pollen grains was placed in a Petri dish with highly moistened filter paper. Germinated pollen grains were counted and the length of pollen tubes was measured after 24 hr of germination. The work was carried out with a PZO Warszawa microscope using an eyepiece micrometre at a magnification of 250×. The obtained data were processed using the Excel program.

The biochemical analysis of the fruit samples was performed using the following methods: high-performance liquid chromatography, quantitative and qualitative identification of compounds (Fratianni et al., 2018; Forcada et al., 2019; Su et al., 2020; Tsaturyan, 2021; Petruccell et al., 2023) and physical and chemical methods of analysis (Kafkaletou et al., 2019; Zhou et al., 2020; Fratianni et al., 2022; Ulikhanyan et al., 2022). The determination of antioxidant activity was performed using the titration method of potassium permanganate in sulphuric acid solution at room temperature (Djenidi et al., 2020; Butkeviciute et al., 2022). The resulting value indicates the antioxidant activity of all biologically active substances.

The investment costs for planting and maintenance and the income and profit from the sale of the crop were calculated. By subtracting the investment costs from the total cash income, profit was calculated. By dividing the profit received by the invested amount and expressing it as a percentage, we obtained the economic efficiency. The cost was calculated by dividing production costs by the amount of planting material obtained per hectare (Davtyan and Voskanyan, 2004; Davtyan and Danielyan, 2007; Melqumyan, 2014; Harutunyan, 2021).

‘Shlor-Tsiran’ is a tall tree with a length of 2.5–4 m with a spherical crown and greyish-brown branches (Figure 1). The number of lateral branches is up to 17. Based on the nature of growth, which is determined by the degree of deviation of the trunk from the vertical direction and curvature around its axis, it belongs to the group of cultivars with a strongly curved trunk. Branchlets are numerous, glabrous, yellowish-light-brown colour. The leaf blade is ovate to elliptic ovate, 4–8 cm × 2.5–5 cm, abaxially pubescent along veins, adaxially yellowish-green, glabrous, shortly acuminate apex, broadly cuneate to rounded basely, irregularly serrate margin and petioles of 2.5–2.8 cm thickness. Flowers are usually solitary, opening before leaves, white or pall pink, small, 1.5–1.7 cm in diameter, peduncle finely pubescent and 3–6 mm long (Figure 2A).

Figure 1.

Figure 2.

Corolla of 5, sometimes 6–7, petals is white, up to 8–9 mm × 6 mm, broadly elliptic to spatulate, with a short claw; hypanthium is 6 mm long, reddish, campanulate, glabrous, sepals 3.5–4.0 mm × 2.2 (2.3) mm, reddish, elliptic, glabrous, with glandular hairs along the margin, apex obtuse and peduncles of 7–12 mm length after flowering ends (Figures 2B and 2C) and stamens are 25–35 in number, 5–6 mm long, style length of 10–12 mm and thinly pubescent ovary. Fruits are small, 38 mm × 40 mm × 40 mm, weighing about 25–40 g, almost spherical in shape, slightly compressed from the sides, with a rounded base and a flat top (Figure 2D). The groove is shallow, slightly deepening at the base and the funnel is spacious. The fruit peduncle is green and up to 12 mm long. The fruit skin is dense, dark purple in colour, glaucous and covered with thin velvety pubescence. The pulp is friable, somewhat mealy, low juicy, adnate to the stone, yellowish red, sweet and sour, with a slight aroma. Stone is of 2–2.6 cm × 1.4–1.7 cm × 0.8–0.9 cm, ovoid in shape with a strongly protruding keel-shaped central rib; surface is longitudinally furrowed, scabrous, slightly wrinkled and pitted (Figure 2E).

The kernel is bitter and rarely sweet. Flowering is observed in the end of March and the beginning of April, and fruit ripening is observed in July.

A comparative study of the morphological characteristics of black apricot cv. ‘Shlor-Tsiran’ confirms the intermediate position in most morphological characteristics of black apricot ‘Shlor-Tsiran’ between parent species of apricot and cherry plum (Table 4).

‘Shlor-Tsiran’ leaf blade shape is an intermediate between apricot P. armeniaca and cherry plum P. cerasifera, but the top of the leaf suddenly shortly acuminated looks like in apricot leaf; the length of the petiole almost coincides with the length of the apricot petiole. Flower stalk length is one of the main distinguishing features of Prunus × dasycarpa cv. ‘Shlor-Tsiran’ (7–12 mm) and approaches with that of cherry plum, whereas in apricot flower stalk is almost absent or very short (1–2.5 mm). With bright pink colour of the sepals, it looks similar to an apricot and differs in colour from the green sepals of the cherry plum. The fruit of ‘Shlor-Tsiran’ is smaller than that of an apricot, which is usually pubescent. Skin colour is dark purple, pulp fibrous, juicy, sweet and sour, reminiscent of large-fruited cherry plum cultivars, but it has an apricot flavour. The stone is not separated from the pulp, which is usually observed in cherry plum. Like cherry plum, black apricot ‘Shlor-Tiran’ is characterised by the qualities such as winter hardiness. It tolerates spring frosts better than P. armeniaca, and much less often than apricots it is affected by fungal diseases such as moniliosis and clasterosporiosis, which makes this crop promising.

The results of our pollen study show that, compared with its parent species, the pollen of Prunus × dasycarpa is characterised by smaller pollen grains, low fertility (38%), high sterility (60%) and very low germination (only 3.4%). The length of germinated pollen tubes of Prunus × dasycarpa after 24 hr of germination mainly ranges from 70 to 270 μm, reaching 500 μm in rare cases. In P. armeniaca, along with high germination, pollen tubes reach 1500–1750 μm, which makes it very difficult to measure them. The viability of P. cerasifera pollen is also very high. After 6 hr of germination, it reaches 86.5% and the length of the pollen tubes is 210–840 μm. Table 5 presents some pollen characteristics of Prunus × dasycarpa, P. armeniaca and P. cerasifera. A decrease in pollen fertility is a characteristic of many interspecific hybrids of fruit crops of Rosaceae family (Kostina and Ryabov, 1960; Papikhin et al., 2011; Eremin, 2016, 2018). It has been established that a very low percentage of normally developed pollen grains in distant hybrids is the result of meiotic anomalies in reduction and equation divisions during microsporogenesis (Papikhin et al., 2011). In our studies, all studied accessions of P. armeniaca and P. cerasifera are characterised by a high level of fertility and viability of pollen (Table 5).

The low percentage of abortiveness and high germination of pollen of wild-growing forms of apricot in Armenia are also noted in the study by Hambartsumyan et al. (1977). The hybrid cv. ‘Shlor-Tsiran’ is, however, characterised by a significant decrease in the fertility and viability of pollen (Table 5 and Figures 3A and 3B). According to Eremin (2016, 2018), who identified four levels of incompatibility of interspecific hybrids, black apricot Prunus × dasycarpa (P. cerasifera × P. armeniaca) belongs to the second level of incompatibility of parental species. There is a decrease in pollen fertility in hybrids from crossing species at the intersectional level within one subgenus, which is confirmed by the low fertility revealed by our studies in Prunus × dasycarpa cv. ‘Shlor-Tsiran’.

Figure 3.

The phytochemical characteristics of ‘Shlor-Tsiran’ ripe fruits are reassumed in Table 6. The cultivar has some interesting phytochemical characteristics, one of which is the absence of sucrose (hence disaccharides) in the fruit pulp. Sucrose levels usually drop during fruit ripening with the resulting increase in fructose and glucose (Borsani et al., 2009). ‘Shlor-Tsiran’ seems to contain mainly glucose. Although unusual, it somehow may reflect its hybrid nature. P. cerasifera is usually low in sucrose and has a higher glucose/fructose ratio (Božović et al., 2017; Murathan et al., 2020), which is however not usually the case for P. armeniaca (Asma and Ozturk, 2005; Alajil et al., 2021). Compared with commercial apricot cultivars, black apricot cv. ‘Shlor-Tsiran’ has a low-medium antioxidant potential and relatively low-medium sugar and organic acid content (Alajil et al., 2021; Tareen et al., 2021; Saeed et al., 2021).

‘Shlor-Tsiran’ is thus a lower-calorie, refreshing alternative to modern cultivars having lower nutritional values and thus presenting a good snack for a low-calorie diet with an adequate intake of antioxidants and vitamin C. Its fruit has higher water and mineral content and, due to its lower preservative characteristics (lower content of sugars and organic acids), a shorter shelf life. This may be due to its relative rarity, as it gained mainly the place of a seasonal short storage fruit for the local market.

Before implementing agronomic measures in production, their technical and economic substantiation must be completed. In this regard, it is necessary to find out that these measures respond to vital problems from the point of view of individual and national interests and correspond to market demands, and what will be the market and socio-economic consequences of increasing production and increasing efficiency. Black apricot stands out for its high yield, which provides a yield of 13.3 trees per hectare.

The justification of the economic efficiency of the black apricot cultivar was obtained for about 10-year-old trees with an average data of 3 years/SD = 63.88) (Table 7). Black apricot stands out for its high yield, which provides a yield of 13.3 trees per hectare. Taking into account the costs of garden care, a high level of profit and profitability is recorded, which is evident when evaluating the economic efficiency of growing the cultivar. Ten-year-old trees in the garden, which is the object of the study, are considered productive, and the yield was high. Depending on this, we had a production cost of 225 drams = 0.5829 $ · kg⁻¹. It was found that cv. ‘Shlor-Tsiran’ is a relatively profitable fruit type and fully compensates the costs of garden establishment and care. The profitability level is 77.3%. Profitability levels are even higher in subsequent years of cultivation.

Although there is growing interest in the breeding of new interspecific stone fruit cultivars, the artificial hybridisation in the genus Prunus has shown to be rather complicated (Soldatov and Salaš, 2007; Nicolás-Almansa et al., 2023). However, a number of artificial hybrids of black apricot are known (Soldatov and Salaš, 2007; Eremin et al., 2021). Although these have been selected for commercial fruit production, it must be noted that their fruit yield is comparable to ‘Shlor-Tsiran’, which is a natural hybrid. The disease and frost resistance of ‘Shlor-Tsiran’ make it an interesting candidate for breeding programmes to develop better grafting rootstocks and promising new fruit cultivars (Eremin et al., 2021). Unfortunately, old local cultivars like ‘Shlor-Tsiran’ are underrepresented in germplasm collections and the decline of its cultivation is a serious threat to the conservation of this black apricot cultivar. In fact, while at least three phenotypic cultivars of ‘Shlor-Tsiran’ (black, pink and yellow) have been mentioned (Vermishyan et al., 1958), we could collect only one cultivar during our extensive fieldwork. The re-establishment of living collections of old native fruit cultivars and phenotypes is definitely a priority to conserve the rich heritage of folk selection in Armenia and apricots in this sense should receive special attention, including the cultivar forms of ‘Shlor-Tsiran’. Also, modern micropropagation methods, established and developed for apricot propagation, should be applied on ‘Shlor-Tsiran’ to achieve efficient amplification of the propagation of rare phenotypes and to conserve and cultivate this nowadays rare natural hybrid (Kovalchuk et al., 2017, 2018).