Influence of polypropylene colored covering material on resistance to low and high temperature stressors in the uterine plantings of strawberries

Introduction

Long-term monitoring of the system “weather factors - soil – plants” in agrocenosis revealed its instability and damaging stress factors that significantly affect the physiological state of the strawberry plants at rest and after leaving it. The main stress factors affect on their own, but often in combination with various intensity and lead to freezing, damping-off, waterlogging of strawberry plants [1]. Analysis of Michurinskaya weather station observations of a 60 year period showed that the degree of repeatability of adverse conditions for strawberry plants wintering was about 62% in November, 28% in December, 5% in January and March. Given the fact that the active growing season on the territory of Black Earth Belt may be limited by adverse weather factors, the conventional cultivation of strawberry nursery is considered a two-year cycle. In this regard, the urgent problem is to find ways to reduce the risks of low temperature stressors on strawberry plants in mother plantations and management of rosettes rooting. One of the possible ways to protect strawberry plants from environmental stressors in the autumn-winter and spring periods is a manufacturing operation of sheltering with polypropylene covering materials, which resulted in the operational control of hydrothermal, air and light regimes for the mother plantations of strawberries.

As a result of previously conducted research (2008 - 2011.), we found a significant effect of density (60 to 100 g / m2) of white polypropylene covering material on a vegetative productivity of mother strawberry plants, plant resistance to freezing and on seedling quality indicators (number of leaves and conducting roots). However, in some years, we identified marginal leaf necrosis of uterine plants and strawberries outlets under cover of white color as a result of exposure to intense solar insolation in the early spring in the absence of snow cover [3]. The works of some foreign researchers established the effect of red, green and blue coating on the vegetative growth and yielding in different groups of plants for greenhouses and open fields [6, 7, 8].

In this regard, the study included a polypropylene covering material “Spunbond” of different colors: white, red, blue (60 g / m2 UV), in order to assess their impact on the resistance to a complex of adverse factors in the pre-winter, winter and spring periods, and plants development in the formation of high-quality strawberry planting material.

Research Methods and Materials

Field studies were carried out in 2011-2013 for experimental mother plantings of strawberries, which are located on leached heavy loam black mould, with a medium acid reaction (pH 4.9). The soil is characterized by a high content of exchangeable potassium and phosphorus and low content of nitrogen, copper, zinc, manganese, calcium. As objects of study we used 13 varieties of strawberries: Vima Zanta, Vima Tarda, Honeoye, Kimberly, Vicoda, Polka, Elsanta, Sudarushka, Divnaya, Festivalnaya Romashka, Ostara, Selva, Vima Rina. Strawberry plants classified as “elite’ were planted in the spring of 2011, according to the general scheme of planting - 1.4 x 0.25 m. Watering of mother plants was performed via irrigation method in accordance with generally accepted regional recommendations. The experiment was laid out in a three-field repetition of 70 m2. as follows:

1. Shelter variant- “spunbond” white, 60g / m2 UV

2. Shelter variant- “spunbond” blue, 60g / m2UV

3. Shelter variant- “spunbond” red, 60g / m2UV

4. Control - without shelter

The methodological basis of the research were: “Workshop on Agricultural Meteorology” [4], “ The Program and Methods of Variety Study of Fruit, Berry and Nut crops” [5], “Techniques of field experience” [1].

Results and their discussion

As a result of air temperature monitoring under polypropylene cover material with density of 60 g / m2 UV in the autumn of 2011 along with insufficient snow cover (0 - 4 cm) the difference between the variant and the control fields was about 3.5 to 9,5⁰ C, which helped avoiding significant effect of low temperature stressors on vegetative and generative organs of strawberry plants. No significant difference was revealed between versions with colored polypropylene covering materials in the period of temperature decrease to critical values ​​(-10-16,5^0C) (Figure 1).

Figure 1. Dynamics of the air temperature under the cover material in the mother plantings of strawberries in autumn 2011 (8 hours).

Apart from this, we traced some of the differences between the options in the initial period of application of shelters. In the variant with red polypropylene material temperature indicators were +3.5 - +3,0⁰C higher compared to the control, which provides a longer period of leaf photosynthesis. The temperature of the soil in the autumn under the shelters varied from +1 to + 4 and generally provided a positive climate for rosettes rooting and accumulation of carbohydrates in uterine plants and outlets (Figure 2).

Figure 2. Dynamics of soil temperature under the cover material in the uterine plantings of strawberries in autumn 2011 (8 hours).

Against the background of snow cover lack in autumn-winter period, we found that the temperature conditions in the shelter depended more on the air temperature (r = 0,88-0,91) than the height of the snow (r = 0,19-0,21).

Observations of the changes in air temperature under the shelter in the spring of 2012, which was characterized by an abnormally rapid transition to the accumulation of the sum of active temperatures above + 10 ° C, showed that the variant with red shelter had lower air temperature values (+10 - + 26⁰C) than the variant with blue color (+14 - + 35⁰C) (Figure 3).

Figure 3. Dynamics of the air temperature under the cover material in the uterine plantings of strawberries in the spring of 2012 (8 hours).

This should be taken into account when selecting a site for the placement of the mother plantations and managing delivery of freshly dug seedlings in different regions of Russia.

An analysis of the results of experiments in 2011-2012 revealed that in spite of the adverse conditions of autumn (lowering of the temperature to 16.5 ⁰C, the formation of ice crust, the absence of snow cover, etc.), seedlings of strawberries in variants with polypropylene covering material of white, blue and red colors showed high winter hardiness and good general condition (score of 4-5). Good general condition was noticed for: Vima Zanta, Vima Tarda, Honeoye, Kimberly, Polka, Sudarushka, Divnaya, which were covered with a polypropylene material “Spunbond” of 60 g / m2 UV of white and blue color (5-4,5 points).

Morphological indicators of quality (diameter of buds, their number, root length, number of leaves) of strawberry seedlings of first reproduction were not significantly different in different color variants at the time of digging, and in the degree of development of leaves, length of petioles we highlighted the blue polypropylene. The evaluation of the varietal characteristics in the formation of morphological indicators of seedlings quality revealed the varieties of intensive type in the number of buds and their diameter: Vicoda (1,8 pcs. and 18mm), Vima Tarda (1,6 pcs. and 14mm), Honeoye (1,3 pcs and 14mm). The quality assessment of strawberry planting material of 10 promising varieties showed that the number of seedling leaves of first commercial grade exceed the standard of the Russian Federation by 160%, while the second - 145%; and the length of the root system at 38.6 and 48% respectively; cone diameter - 50% of the first quality grade.

The study of the stability of strawberry plants in conditions of complex adverse environmental factors of autumn-winter and spring seasons in strawberry nursery in the technological cycle of 2012-2013 showed that in spite of the adverse conditions of autumn-winter period of 2012 (decrease of temperature to -16,2-18,6⁰C, with little snow cover - 5 to 6 cm), strawberry seedlings in all variants with shelters showed a high degree of hibernation compared to the controlled where the mother plants and seedlings of strawberry had leaf damage of 80% and parenchyma tissues up to 2 - 3 points. Results of autumn-winter air temperature measurements under the polypropylene covering materials showed a less pronounced advantage under the red polypropylene cover material in the initial period of their application (+ 1- + 2 ° C) compared to the previous season (Figure 4).

Figure 4. Dynamics of the air temperature under the polypropylene covering materials in the mother plantation in autumn 2012 (8 hours).

Along with this, a smaller range of variation in air temperatures was noticed between the variants and the control shelters than in the previous season. This is probably due to the higher soil moisture in the pre-winter period, as it was raining more heavily October 2012, over 55.9 mm, compared to historical averages. Soil moisture reserves in this period amounted to Apah - 35 - 47 mm, and in the soil layer of 0-50 cm - 107 mm at a background of an increase in average air temperature (at + 4,2⁰S). However, the temperature of the soil under the shelter of red and blue color ​​exceeded the control variant and the variant of white color. When the critical temperature was approached (-17,7-19⁰C), and the snow height was up to 5 cm, soil temperature did not drop below 0⁰C in all shelters (Figure 5).

Figure 5. Dynamics of soil temperature under the polypropylene covering materials in the mother plantation in autumn 2012 (8 hours).

In the early spring of 2013, there was rapid melting of snow (height reduced from 35 to 0 cm), with the depth of soil freezing about 30 cm. This led to inadequate absorption of meltwater in soil and development of physiological disorders in the form of waterlogging and increased plant leaf necrosis, especially for Vima Zanta, Kimberly, Sudarushka, Festival Daisy. Thus, after the wintering, the degree of freezing of vegetative organs (leaves) was 2-3 points (30-40%) in cases with shelters of white, blue and red colors and did not depend on the color of polypropylene material.

Monitoring the air temperature under the shelter in the early spring (after the snowmelt) showed that in variants with polypropylene shelter of red, blue and white colors, the figures were close, but they were significantly higher than the control variant with the temperature growth (in the second half of April) and thawing of the soil (Figure 6).

Figure 6. Dynamics of soil temperature under the polypropylene covering materials in the mother plantations in the autumn 2013 (14 hours).

The study of vegetative productivity of promising varieties of strawberries in the mother plantations determined quality metrics of strawberry seedlings. Morphological indicators of quality (diameter of the buds and their number) of strawberry seedlings were not significantly different for different shelter variants at the time of digging, and the number of leaves and their area, the ​​development was the best in the variant with polypropylene of blue and white colors. In the second year of operation of uterine plantings of strawberries, the evaluation of the quality of planting material of 10 promising varieties showed that the number of leaves in seedling of the 1^st commercial grade was 145% higher than the standard value, and 2^nd grade - 245%; the length of the root system was 78.6 and 116%; cone diameter - 25% and 8.8% respectively. Seedlings of the first commercial-grade formed an average of 1.1 bud. At the same time it was determined that output of the first commercial grade in general was 89.2% in the first year of uterine plants and 49.8% - in the second year.

Conclusions

· The influence of polypropylene covering materials of different colors (red, white and blue) 60g / m2 UV increased resistance of mother plantations to environmental stressors of autumn-winter and spring seasons and increased the output that met the standards of planting material.

· We identified trends of higher air heating under blue polypropylene shelters in early spring, which resulted in the increased degree of leaf petioles of strawberry plants that must be taken into account when rearing planting material.