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 Tomatoes are leading vegetable crop in an open fields as well as in greenhouses in Uzbekistan. 20% of fresh tomatoes from the open field production and almost 60% from the protected areas go to the export, and it makes tomatoes economically valuable crop which can increase income of greenhouse farmers. Due to sharp increase in recent years areas under plastic greenhouses in Uzbekistan, it became necessary the selection of tomato hybrids for growing in a such constructions. Presumably, nowadays in Uzbekistan almost 90% of greenhouses are covered by plastic film, and basically it is a LDPE.

 In the early 70’s of the last century in greenhouses were grown only few tomato varieties, however by the development of protected horticulture increased also demand for the special varieties for different greenhouse constructions which should have higher yields, good marketable view, complex resistance to the main diseases, and good growing abilities even in a low light and temperature conditions. In winter-spring growing season (January-June) greenhouse vegetable crop hybrids should to have a high fruit setting abilities, especially in a low winter and following a high spring temperatures (Volkov et al, 1966).

 In 2010 under the scientific cooperation with Korea Project of International Agriculture (KOPIA) and by support of Rural Development Administration (RDA) on the territory of the experimental station of UzRIVMCP have been constructed greenhouses with double plastic coverage and iron pipe frame (0.15 ha). Objectives of the present trial were to evaluate and select more suitable tomato varieties for growing in double layered plastic greenhouses in the climatic conditions of Tashkent region, and recommend them to the State Variety Testing for further evaluation.

Materials and Methods

Overview of climatic conditions.

 Tomato variety trials were carried out in winter-spring season of 2011-2012 at the experimental station of Uzbek Research Institute of Vegetable, Melon crops and Potato, Tashkent region, Uzbekistan. Location of the experimental station reflects the general features of the climate of Tashkent region and whole Uzbekistan. By the climate Tashkent region belongs predominantly to the piedmont zone; with an abundance of solar radiation and heat, the main factor limiting of utilization of agro-climatic and soil resources is the lack of irrigation water (Muminov and Karnaukhova, 1981; Chub, 2000). The annual radiation balance in the lowlands of the Tashkent region is 2100- 2300 MJ/m². The average annual temperature is + 13.0... +14.0℃, the average minimum temperature is + 3.1... +5.5℃, with an absolute minimum of -28.0...-35.0℃, the average maximum temperature is +36.0...+36.5℃, with an absolute maximum of +43.0...+47.0℃, daily amplitude of air temperature is +13.0…+18.5℃. The frost-free period is 220 days. The period with temperatures above +5.0℃ is 268 days (from 11 March to 3 November), above +10.0℃ – 190 days (from 25 March to 31 October), above 15.0℃ – 173 days (from April 14 to October 5). The sum of effective temperatures above +5.0℃ is 3490.0℃, above +10℃ – 2290.0℃ and above +15.0℃ – 1310.0℃. In the plain areas of Tashkent region fall 206-316 mm precipitation annually. Most precipitation occur in late autumn, winter and early spring periods from November to March. The relative humidity in winter is 80-90%, in summer –20-30% (Anikeyev and Ahn, 1974; Anikeyev 1988; Konovalova, 1974).

 Seven varieties of tomato including standard variety (Table 1) were evaluated in single span, plastic double-layered greenhouse. Greenhouses were passively heated, manually vented: air circulation was carried out through roll-up side-walls.

Table 1. Tomato varieties used in trial

 During winter months greenhouses were heated with hot air heaters. Greenhouses were equipped with drip irrigation system controlled automatically. Prior to transplanting black plastic mulch film (thickness-0.03 mm) laid on prepared raised beds after drip system installation.

 Growing procedure. Tomato seeds were sown into the transplanting pots (10 × 10 cm) on the first decade of January and after 45 days (from first appearances of seedlings) transplanted into the greenhouse. Soil in greenhouses was silt loam also is known as a typical sierozem was slightly saline (Table 2).

Table 2. Soil properties in greenhouses

 Before transplanting soil was plowed for 20 cm, manure compost was added as an organic amendment, also rice husk and river sand was added to increase soil friability. Tomatoes were grown on a black plastic mulch with drip irrigation and conventional soluble fertilizers. Tomato transplants were transplanted onto the double rows with 80 cm spacing between the rows and 40 cm between plants on each row. 120 cm walkway was considered between 2 double rows. Then plants were tied to the strings supported with overhead wires, stem formed as a single stem. During the growing period 5 foliar nutrient applications were applied (2500 l/ha per application). After the appearance of the 7^thcluster, plants growing point was removed to stimulate growth and development fruits in lower clusters (conventional growing technique). Standard variety for our trials was F₁ Belle - popular commercial hybrid among greenhouse farmers. Trials were conducted in randomized complete block design with four replications. Data was analyzed using Analysis of Variance (ANOVA) procedure, and treatment means were separated using Fisher’s Least Significant Difference Test (p < 0.05).

Results and discussion

 In winter-spring growing season greenhouse tomatoes should have a strong stems with short internodes because plants tend to have a high fruit load in conditions where gradual increase of air temperate and solar radiation occurs. Research shows that all evaluated hybrids has the same growing habits except for local cultivar Turon, which growth and development in greenhouses were relatively weaker in comparison with F₁ hybrids (data is not given).

 There were significant difference among tested cultivars in average fruit weight. Fruit weight ranged from 120 to 225 g. It should be noted that in Uzbekistan the most popular fruit size among population is varied from 150 to 220 g for medium and beef tomato fruits respectively. Since F₁ Chelbas had fruits with average weight of around 120 g, however they had intensive red and uniform colored skin, shiny appearance and well marketable view. Marketable fraction of the total yield for all tested varieties was high, and consisted 95-98% from the total yield. The fraction of unmarketable fruits consisted predominantly from fruits with physiological disorders (sunscald, skin cracks, blossom end rot).

 High significant differences in yield were observed among tested tomato varieties. Total yield was ranged from 15.8 to 19.3 kg/m². Significantly high total as well as a marketable yields were obtained for F₁Beton and F₁Chelbas compared to standard variety (Table 3).

Table 3. Mean fruit weight and marketable yield of tomato varieties

 Two local hybrids F₁Saykhun and F₁ Bahor also showed higher marketable yield in comparison with standard, however they were not significantly different. The lowest yield (15.2 kg/m²) was observed for cultivar - Turon.

 Tomato prices are highly fluctuating during course of the year (Fig. 1). It’s important to start harvesting earlier, and to harvest mostly in spring months, since relatively high prices for fresh tomatoes remain until June when production from non-heated plastic tunnels and open field starts to fill vegetable markets (Bakuras, 1989).

Fig. 1. Dynamics of monthly average prices for tomato fresh fruit in 2008-2010 (Quylik wholesale market, Tashkent, personal observations).

 Relatively high content of sugar (3.9%) and vitamin C (14.4 mg/%) was observed in fruits of domestic variety -Turon (Table 4). The smallest content of sugar (3.16%) and vitamin C (13.0 mg/%) was observed in standard variety – F₁ Belle. Nitrogen (N-NO₃) accumulation in all tested varieties was low - 19.3-34.5 mg/kg of wet fruit weight, since maximum allowable concentration for greenhouses tomatoes is 150 mg/kg (Nuritdinov, 1988).

Table 4. Tomato fruits dry matter, vitamin C and sugar content

 Early marketable yield (until May 1) was not significantly differ among tomato varieties, however slightly higher early marketable yield was obtained from hybrid F₁ Beton (Fig. 2). In all tested varieties a bulk of the total yield (~80%) was harvested between May and June. In our trials seeds were sown relatively late compared to sowing dates recommended in standard production guides. To increase early yield in winter-spring season it is recommended (Khoshimkhujaev, 2009) sowing tomato seeds on the first decade of November with further transplanting of 45-50 days-old seedlings in greenhouses on the first decade of January. Standard recommendation developed by UzRIVMCP also recommended early sowing and transplanting dates (Bakuras and Lutsenkova, 1985; UzRIVMCP, 2007) to increase the fraction of the early yield.

Fig. 2. Harvest dynamics of 7 tomato varieties.

Conclusion

 Greenhouse tomatoes are highly valued vegetable crop in Uzbekistan. In winter-spring growing season tomatoes can be grown without supplemental lighting, moreover relatively mild winter conditions gives opportunity to reduce costs for greenhouse heating when used modern greenhouse construction and high-yielding varieties. Many research results showed that double layered plastic greenhouses can be more energy efficient in comparison with single layered greenhouses. In this context double layered plastic greenhouses can be a good option for greenhouse farmers to increase profit from vegetable production by decreasing heating costs.

 In 2010 in the experimental station of Uzbek Research Institute of Vegetable, Melon Crops and Potato double-layered plastic greenhouses were constructed in cooperation with Korea Project on International Agriculture. Investigations have been started on energy saving abilities of these greenhouses in comparison with conventional single layered greenhouses in Tashkent regions climatic conditions. In our trials seven tomato varieties were tested in double-layered plastic greenhouses. The highest yield was obtained from F₁ Beton and F₁ Chelbas in comparison with standard variety. However further investigation will be needed to evaluate the resistance to common pests and diseases and fruit quality of these varieties.