Introduction

In the system of virus-free seed production of potato, the application of plant growth regulators is promising. These growth regulators facilitate smoothing of stress phenomena, which occur during transplantation of microplants to qualitatively new conditions and production of high-quality seed potatoes (Cheremis, & Yakimova, 2011; Lobachev, & Avdienko, 2010). That is why in many countries growth regulators are successfully incorporated into the complex of measures for the cultivation of improved potatoes (Sasse, 2003; Krishna, 2003; Kagale, et al., 2007; Arteca, & Arteca, 2011; Mitchell, et al., 1970).

However it would be wrong to assume that growth regulators cause new immune properties in plants. Effect of these substances is limited by genotypic features of plants, and appears only in phyto-immune correction of own immunity (Zasorina, et al., 2010).

According to many researchers (Vladimirov, & Fomin, 2008; Eagles, 2004; Zeyruk, 2000), plant growth regulators are structural (physiological) analogues of phytohormones. They have the ability to actively influence the hormonal balance of plants, enhance the resistance to a number of pathogens that affect the adaptive properties of potatoes (Zasorina, et al., 2010).

A promising growth regulator is Epin-Extra, developed by NSPP “NEST M”. Epin-Extra is a synthetic brassinosteroid, analogue of epibrassinolide, natural plant hormone. Epibrassinolide is a phytohormone that regulates the activity of other plant hormones necessary for plant life: auxins, gibberellins, cytokinins, abscisic acid, ethy0 lene. Application of Epin-Extra increases the potato resistance to environmental stress (drought, excessive moisture, frost) and diseases. Epin-Extra displays the properties of a non-specific immunomodulator and reduces the content of nitrates in plants (Vakulenko, 2013). In this regard, the goal of our study is to investigate the influence of the growth regulator Epin-Extra on photosynthetic activity and biochemical parameters of the plants during mini-tubers cultivation in protected ground (greenhouse).

Methodology

The experimental work was carried out in the biotech laboratory and the greenhouse of the OOO (LLC) “Elithoz” of the Bor District of the Nizhny Novgorod region. The analytical work was conducted in the laboratory of the Department of Biology NSPU named after K. Minin. In these experiments we used the improved material of potato varieties Udacha (domestic selection) and Red Scarlett (foreign selection). The experimental setup includes 2 options: 1 (control) – standard nutrient medium Murashige-Skoog (MS); 2 (experiment) – MS + Epin-extra (at the last stage of propagation) + treatment with Epinay-Extra at the budding stage. The concentration of the drug Epin in the laboratory experiment – 0.25 mg/l (selected on the basis of published data), in a field experiment – 80 ml/ha.

Field experiments were carried out and statistically processed in accordance with the established procedure (Dospehov, 2011). The total area of the plot was 28 sq. m and the account area – 14 sq. m., experiment repetition – 4-fold, arrangement of the plots – systematic. The scheme of planting – 70 × 24 cm. During vegetation spraying was carried out once over the elevated part of the plants. Treatments were carried out with a hand knapsack sprayer. During the growing season in protected ground (greenhouses), leaf area was determined by the gravimetric method using stamp cutting, according to the procedures of SRIPH (Scientoific Reseacrh Institute of Potato Household (1967, 1989), photosynthetic activity – by the method of Nichiporovich A.A. Accounting for the harvest is made by weighing all the tubers from plots by the method of SRIPH (1967). Biochemical parameters of tubers were determined by conventional methods: starch content in tubers – by unit weight, dry matter content – gravimetric method, nitrates – potentiometrically by GOST (All Union State Standard) 26951-86.

Results

Table 1: Influence of Epin Extra on physiological processes of potato plants in a protected ground (in average for 2011-2013)

Use of Epin-Extra at the budding stage during microplants cultivation in a greenhouse contributed to an increase in the assimilative leaf surface (by 12.4-11.4%) and photosynthetic productivity (by 44.6-36.8%), depending on a variety.

Table 2: Influence of Epin Extra on productivity and quality of potato plants in protected ground (in average for 2011-2013)

Cultivation of improved potatoes in the conditions of protected ground using Extra-Alpin contributed to an increase in yield by 31.9-12.4%, increase in the dry matter content in tubers by 16.5-10.7%, starch by 3.4-2.5 % and a decrease in nitrate content by 32.7-25.4%, depending on a variety.

Discussion

The studies have shown that the use of the Epin-Extra growth regulator at the last stage of micro propagation and treatment of growing plants at the budding phase in the protected ground has had a definite impact on physiological and biochemical processes and ultimately on the productivity of the studied varieties.

According to researchers (Nichiporovich, 1961), the important indicator of productivity and quality of improved potatoes is the leaf apparatus formation of plants, where the initial creation of organic matter and its subsequent transformations to the final products occur. The conducted studies have shown that plants treated with the Epin-Extra drug had a reliable increase in the assimilative surface of both varieties (Table. 1). We observed an increase in leaf surface at the flowering stage depending on the variety by 12.4-11.4%, respectively, compared with the control options. The Udacha variety was the most responsive to the effect of the drug.

The positive moment of this simulation is that the increase in leaf surface led to the increase of photosynthetic processes activity in potato leaves. There is an opinion (Nichiporovich, 1961) that 90-95% of organic matter is created by the leaf surface during the photosynthesis process and up to 80% of assimilants comes to the tubers of 70-day-old plants.

The qualitative characteristic of leaf apparatus activity is the amount of net productivity of photosynthesis. As phenological phases passed the net photosynthetic productivity increased from the budding stage to the flowering stage, from 4.7-8.1 to 4.4-7.8 g/sq.m per day, depending on the variety (see Table 1). The maximum productivity of photosynthesis was observed on the Udacha variety (44.6%), lower productivity (36.8%) – on the Red Scarlett variety at the flowering stage with the Epina-Extra treatment. Before harvest the photosynthetic productivity of the Udacha variety decreased by 1.6-2.8 times, of the Red Scarlett variety – 1.6-2.5 times, respectively. Therefore, with the Epin-Extra treatment the outflow of assimilants into the tubers of both varieties enhances for the same period of time, which leads to increased productivity and better quality of potatoes. The data presented in Table 2 proves this point. According to this data, the photosynthetic apparatus work had an impact on yield formation of tubers. The use of the Epin-extra drug during microplants cultivation with the seedling method in protected ground helped to improve the yield of the studied varieties. The greatest yield increase is obtained from the domestic selection variety Udacha. In this case, in average for three years a credible increase in the control based on a single plant of the given variety amounted to 35.6%. A smaller but also a credible yield increase was obtained from the variety Red Scarlett (12.3%).

Apparently, the Epin-extra growth regulator, when adding it into an artificial nutrient medium and treating vegetating plants with this drug at certain concentrations, has high biological activity. This further promotes the growth and development of plants (both in in vitro culture and in protected ground) and also enhances the immune potential of greenhouse plants, and therefore increases the photosynthetic activity, and as a consequence – yield, particularly of the domestic variety. The stimulating effect of brassinosteroids on photosynthetic processes and yield is shown previously for other crops and wild plants (Sasse, 1997; Gregory, 1981; Zhang, et al., 2009).

The quality of tubers is a complex indicator, which is formed in the process of potatoes cultivation, which depends on the variety, soil and climatic conditions and agricultural practices (Karmanov, et al., 1988). Among key indicators of potato tubers’ quality the crucial one is the contents of starch and dry matter (Kulikov et al., 1988).

The qualitative analysis of the product showed a tendency of an increase in the content of dry matter, starch and decrease of nitrates in tubers with the Epin-Extra use on both varieties (Table 2).

Compared with the control group, the use of the Epin Extra contributed to the largest increase in dry matter content (16.5%) and starch (3.4%) in the tubers of the Udacha varierty. The drug contributed to increased biochemical parameters to a lesser extent for the Red Scarlett variety (by 10.6-2.4%, respectively). The data of analyses indicates slight differences in the content of qualitative indicators by the years of research, since agro-climatic conditions in the greenhouse are not dependent on weather conditions, this is also supported by the results of other researchers (Karmanov, et al., 1988; Uromova, 2010).

The assimilation of nitrates in plants is a natural process and to a greater extent depends on the number and ratio of mineral elements in the soil, weather, agrotechnical practices and varieties of potatoes. Nitrate accumulation in plants is a consequence of metabolic disorders, whereby absorbed nitrogen is not fully used in the synthesis of amino acids, and later in the synthesis of proteins, i.e. not all absorbed nitrates are reduced to ammonia (Polevoy, 1982). Therefore, the presence of nitrates in agricultural products does not raise concerns. Another matter is in what quantities these substances are present, as if they accumulate in the tubers above the MPC norm, they can harm human health (Dmitrieva, 1983).

In our studies, the maximum nitrate accumulation is observed in the control options of both varieties, the excess of this indicator in the Red Scarlett variety was not significant. Less nitrate accumulation was noted when using the drug Epin-Extra on both varieties, however, the Udacha variety had the minimum content (31.3 mg/kg). From this we can conclude that the accumulation of nitrates has a varietal specificity and growth regulators allow plants to include nitrogen compounds in metabolism better and not to put them away in plant organs in the form of nitrates (Dyakov, 1990; Kovalenko, 1997; Uromova, 2009).

Conclusion

The findings can be explained by the fact that the drug Epin-extra is a stress adaptogen with strong growth stimulating and immune protection activity. Epin-Extra enhances photosynthetic processes, increases the yield and its quality in protected ground. There is an opinion (Prusakova, & Chizhova, 1996) that brassinosteroids have little effect on the level of physiological and biochemical processes under normal growing conditions. Their effect is more noticeable under stressful conditions such as transplant of microplants and high temperatures in the greenhouse conditions. This allows us to state with certainty that this drug can compete effectively with chemical pesticides, as it is characterized by high biological activity, which ultimately leads to increased productivity of potatoes with low costs of labour and material resources, and provides environmentally friendly products of high quality.

As a result, the studies have provided positive data on Epin-Extra effect on assimilative leaf surface, net photosynthetic productivity of plants and their subsequent crop and its quality in protected ground. However, in the course of the experiments we did not examine the effect of the drug on disease resistance of plants (peroxidase activity) of the improved potato in a greenhouse. We plan to conduct these studies in the next growing season.

Acknowledgement

Researchers express gratitude to the general director of JSC “Elitkhoz” Anatoly Germanovich Pushkov for granting a platform (biotechnological laboratory, the hothouse complex, the revitalized plants of potatoes) for carring out scientific researches.

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