Influence of conditions of seed reproduction of different wheat genotypes on primary resistance to high temperatures and frost

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Institute of Genetics, Physiology and Plant Protection (Chisinau, Moldova)

Ukrainian Scientific Institute of Plant Breeding (Kyiv, Ukraine)

Influence of conditions of seed reproduction of different wheat genotypes on primary resistance to high temperatures and frost

О.Р. Dascaliuc

N.V. Zdioruk

T.H. Ralea

N.N. Jelev

Yu.A. Pariy

Ya.F. Pariy

Abstract

Experiments provided with the seeds of 50 wheat varieties reproduced in the Kharkiv region of Ukraine and Chisinau area of Moldova to elucidate the efficiency of rapidly assessing genotypes' primary resistance to high temperatures and frost. The tests were performed under laboratory-controlled conditions, based on the evaluation of the seeds' germination capacity after their exposition to shock with high or sub-zero temperatures. The obtained results demonstrated that by applying the elaborated methods, we could differentiate wheat genotypes by their primary resistance to extreme temperatures (excluding the adaptation processes induced during plant ontogenesis). Resistance of different wheat genotypes seeds to heat shock or shock with negative temperatures may vary, being influenced by the environmental conditions of their reproduction. The data obtained demonstrate that seeds resistance to both types of temperature shock is specific for different wheat varieties and can be influenced by conditions of seed reproduction. Due to this adaptive variability of genetic and epigenetic nature, wheat varieties and their descendants are characterized by high resistance and good productivity in different environmental conditions. The possibility of epigenetic inheritance suggests that it may influence the primary frost or heat resistance of wheat embryos. Because the meteorological conditions vary from year to year, they can influence the primary resistance of genotypes to heat stress factors even when seeds reproduced in the same zone. We consider that the assessment of the primary resistance of wheat genotypes offers new possibilities for determining its interference with other mechanisms of resistance of wheat genotypes to frost or heat. The elaborated methods are with perspectives for implementing in programs for selection or appreciation the heat or frost resistance of wheat genotypes.

Key words: Triticum aestivum L., seeds, heat resistance, frost resistance, accelerated methods

Вплив умов розмноження насіння різних генотипів пшениці на первинну стійкість до високих температур та морозу

О.П. Даскалюк, Н.В. Здіорук, Т.Х. Раля, Н.Н. Желєв, Ю.О. Парій, Я.Ф. Парій

Інститут генетики, фізіології та захисту рослин Республіки Молдова (Кишинів, Молдова)

Всеукраїнській науковий інститут селекції рослин (Київ, Україна)

Анотація

primary resistance genotype wheat

Експерименти проводилися з насінням 50 генотипів пшениці, відтворених в Харківській області України та Кишинівській області Молдови, для з'ясування ефективності швидкої оцінки первинної стійкості генотипів до високих температур і холоду. Випробування, проведені в контрольованих лабораторних умовах, засновані на оцінці схожості насіння після впливу на нього теплового шоку або від'ємних температур. Отримані результати показали, що, застосовуючи розроблені методи, можна диференціювати генотипи пшениці за їх первинною стійкістю до екстремальних температур (без урахування адаптаційних процесів, індукованих в онтогенезі рослин). Стійкість насіння пшениці різних генотипів до теплового шоку або впливу негативними температурами може варіювати залежно від умов середовища їх розмноження. Отримані дані показують, що стійкість насіння до обох типів температурного шоку специфічна для різних сортів пшениці і може залежати від умов розмноження насіння. Завдяки цьому, адаптивна мінливість генетичної і епігенетичної природи різних генотипів пшениці і їх нащадки характеризуються високою стійкістю і врожайністю в різних умовах навколишнього середовища. Можливість епігенетичного успадкування передбачає, що воно може впливати на первинну стійкість зародків пшениці до високих температур та морозу. Оскільки метеорологічні умови змінюються з року в рік, вони можуть впливати на первинну стійкість генотипів до чинників теплового стресу, навіть якщо насіння відтворюються в одній і тій же зоні. Ми вважаємо, що оцінка первинної стійкості генотипів пшениці відкриває нові можливості для визначення її взаємодії з іншими механізмами стійкості генотипів пшениці до екстремальних температур. Розроблені методи перспективні для впровадження в програми з селекції або для оцінки стійкості генотипів пшениці до стресових температур.

Ключові слова: Triticum aestivum L., насіння, теплостійкість, морозостійкість, прискорені методи

Влияние условий размножения семян разных генотипов пшеницы на первичную устойчивость к высоким температурам и морозу

А.П. Даскалюк, Н.В. Здиорук, Т.Х. Раля, Н.Н. Желев, Ю.А. Парий, Я.Ф. Парий

Институт генетики, физиологии и защиты растений Республики Молдова, (Кишинев, Молдова)

Всеукраинский научный институт селекции растений (Киев, Украина)

Аннотация

Эксперименты проводились с семенами 50 генотипов пшеницы, воспроизведенных в Харьковской области Украины и Кишиневской области Молдовы, для выяснения эффективности быстрой оценки первичной устойчивости генотипов к высоким температурам и холоду. Испытания, проводимые в контролируемых лабораторных условиях, основаны на оценке всхожести семян после воздействия на них теплового шока или шока отрицательными температурами. Полученные результаты показали, что, применяя разработанные методы, можно дифференцировать генотипы пшеницы по их первичной устойчивости к экстремальным температурам (без учета адаптационных процессов, индуцированных в онтогенезе растений). Устойчивость семян пшеницы разных генотипов к тепловому шоку или воздействию отрицательными температурами может варьировать в зависимости от условий среды их размножения. Полученные данные показывают, что устойчивость семян к обоим типам температурного шока специфична для разных сортов пшеницы и может зависеть от условий размножения семян. Благодаря этому адаптивная изменчивость генетической и эпигенетической природы разных генотипов пшеницы и их потомки характеризуются высокой устойчивостью и хорошей урожайностью в различных условиях окружающей среды. Возможность эпигенетического наследования предполагает, что оно может влиять на первичную морозо- или теплоустойчивость зародышей пшеницы. Поскольку метеорологические условия меняются из года в год, они могут влиять на первичную устойчивость генотипов к факторам теплового стресса, даже если семена воспроизводятся в одной и той же зоне. Мы считаем, что оценка первичной устойчивости генотипов пшеницы открывает новые возможности для определения ее взаимодействия с другими механизмами устойчивости генотипов пшеницы к экстремальным температурам. Разработанные методы перспективны для внедрения в программы по селекции или для оценки устойчивости генотипов пшеницы к стрессовым температурам.

Ключевые слова: Triticum aestivum L., семена, теплоустойчивость, морозоустойчивость, ускоренные методы

Determining the mechanisms of resistance and adaptation of plants to positive and negative temperatures is of interest in connection with the solution of practical problems of breeding and the predicted global warming (Schneider, 1989). A clear understanding of the mechanisms of plant resistance and adaptation to stress factors is crucial for agricultural specialists since the rational use of varieties and hybrids, optimization of the methods for breeding new genotypes, as well as testing the effects of biologically active compounds on plant resistance and productivity under stress conditions (Levitt, 1980; Udovenko, 1988; Dascaliuc et al., 2013). The mechanisms of resistance to extreme temperatures are complex and depend on plants' morphological, physiological, biochemical, and genetic characteristics. These features' values can vary from genotype, phase of ontogenesis (Zhuchenko, 1988; Ivanov, 2003; Dascaliuc et al., 2013), and the specificity of environmental conditions (Zhuchenko, 1988; Dascaliuc et al., 2013; Fowler et al., 2014). In this regard, it is essential to develop methods for accelerated and separate assessment of the primary (initial) and adaptive plants' resistance to extreme temperatures (Zhuchenko, 1988; Dascaliuc et al., 2013; Fowler et al., 2014). Also, plant resistance and productivity are determined by various avoidance components, leading to a decrease in the exposure dose of the stress factor (Levitt, 1980; Lopes et al., 2010; Dascaliuc et al., 2013).

Scientific literature describes numerous results of assessing the resistance of plants to extreme temperatures. The theoretical generalizations and methods for assessing plant resistance are exposed in (Levitt, 1980; Udovenko, 1988; Dascaliuc et al., 2013). They define various approaches that make it possible to assess the resistance of plants to various stress factors. Bringing to a single common denominator of the abundant data concerning plant responses to stressors, obtained on a different level of organization, is not always possible. In addition to the effects caused by stressors of different nature and intensity, there are also specific features for plant reactions at the sub-cellular (Levitt, 1980; Alexandrov, Kislyuk, 1994; Dascaliuc et al., 2013), cellular (Levitt, 1980; Alexandrov, Kislyuk,, 1994; Dascaliuc et al., 2013), tissue (Alexandrov, Kislyuk, 1994; Ivanov, 2003), organism (Dascaliuc et al., 2013), and ecological level (Zhuchenko, 1988; Lopes, 2014). The variety of stress factors and the specificity of plant responses at different levels of organization complicate developing the consistent methods for assessing their resistance to stress factors. We believe that the principles of systems theory (Novoseltsev et al., 2006; Dascaliuc et al., 2013) and comprehensively developed mathematical models for the accelerated assessment of the stress stability of technical systems (Escobar et al., 2006) can largely contribute to solving this complex problem.

Precise separation of the indicators of primary and adaptive components (Levitt, 1980; Dascaliuc et al., 2013) of resistance is necessary to systematize experimental data and methods for assessing plant resistance to extreme temperatures. It is also essential to consider the input of avoidance (reduction of the exposure dose of the stress factor) (Zhuchenko, 1988; Lopes, 2010; Dascaliuc et al., 2013) to the overall plant resistance to the action of one or another stressor. First of all, it is necessary to determine the primary plant resistance and then proceed to the most accurate identification of adaptation components and avoidance phenomena (Levitt, 1980; Lopes, 2010; Dascaliuc et al., 2013) to the total plant resistance to stress factors. In practice, this turns out to be not easy since, depending on the stage of ontogenesis, various adaptation phenomena superimposed on the primary resistance of plants, the contribution of which is difficult to assess accurately. The use of plant seeds simplifies the problem. The germination parameters of wheat seeds previously exposed to extreme temperatures characterize the initial (primary) plant tolerance to extreme temperatures. As the germination seeds are in the initial phase of ontogenesis, age and adaptation processes deed not influenced their primary resistance to extreme temperatures. However, in these studies, we cannot completely rule out the possible contribution of epigenetic transmission of some traits acquired in the previous generation and transmitted to offspring (Jaligot et al., 2015).

In our studies, we used seeds of different genotypes of hexaploid wheat reproduced in the climatic conditions of the Kharkiv region of Ukraine and the Chisinau area of Moldova. We appreciated the possible influence of environmental conditions of seed reproduction on wheat genotypes' primary resistance to heat or frost. By exposing the seeds of 50 varieties and lines of wheat cultivated in the Kharkiv region to a specific dose of heat shock, or shock with negative temperature, it was possible to distribute wheat genotypes according to their primary resistance to positive or negative temperatures. Based on the obtained results, we selected ten genotypes, which, according to their primary resistance to high temperature s, evenly covered the area between genotypes with minimum and maximum resistance. Subsequently, we reproduced the seeds of these genotypes in the Chisinau area and used them for determining their primary resistance to high and negative temperatures. When planning these studies, we considered that the germination of hexaploid wheat seeds after exposure to extreme temperatures, like other physiological characteristics, has genetic limitations. Consequently, seeds of genotypes with a specific breeding history can show different values of individual plasticity and can differ by their level of primary resistance to high temperatures or frost. The objectives of our study were: 1) to evaluate the discriminating ability of the methods based on seeds exposure to a specific dose of heat shock (HS) or shock with negative temperature (SNT) as a rapid, simple, repeatable, and inexpensive method of screening in laboratory conditions of the resistance to extreme temperatures of wheat gen o- types; 2) to evaluate the repeatability of results obtained with the same set of wheat genotypes reproduced in different zones.

Methods

We used in the studies seeds of 10 varieties and 40 lines of hexaploid wheat. In the list below, the first the line numbers, or the name of the variety, are indicated, and then, through a dash, the assigned serial number of the genotype in our analyzes is given: 140-1, 466-2, 423-3, 542-4, 111-5, 1108-6, 506-7, 123-8, Batiko-9, Acter-10, 317-11, 287-12, Samurai-13, 1079-14, Arctis-15, 300-16, 1169-17, 420-18, 594-19, 471-20, 1051-21, 372-22, Shestopalovka-23, 464-24, 857-25, 543-26, 1032-27, 1150-28, 517-29, Skazen-30, 48-31, 37932, 1054-33, 29-34, 87-35, 1014-36, 1087-37, 63438, Kolichuga-39, 83-40, 126-41, 1101-42, 91-43, Odesskaya 267-44, Toulouse-45, 21-46, 1088-47, Ovidii-48, 781-49, 1013-50. The seeds were multiplied in 2015-2016 in the Kharkiv region. In the beginning, they were calibrated by volume, passing through sieves with a diameter of hole equal to 2.42.6 mm. Then the seeds were incubated in 0.1% potassium permanganate solution for 20 minutes and thoroughly washed with tap water, then with distilled water. After soaking in water at +4°C for 36 hours, the seeds were exposed to heat shock (HS) by immersing for a certain time in the water at different temperatures, maintained with an accuracy of ±0.05°C using an ultra-thermostat U10 (Germany). The seeds were shocked by negative temperatures (SNT) by incubation in an air thermostat Rumed 3401 (Germany) for 8 hours, maintaining the air temperature with an accuracy of ±0.5°C.

The first problem was determining the unique value of the incubation temperature (positive or negative) and the duration of exposition, suitable for separating wheat genotypes according to their resistance to high temperatures or frost. Based on the data obtained in preliminary studies, for the distribution of wheat genotypes by primary resistance to frost or heat, we choose the doses provided by exposition of seeds at the temperature of -7°C or +50°C, and the duration of exposition 8 hours or 30 minutes, respectively. Our studies installed two control variants: the first for experiments with determining the wheat genotypes' resistance to frost, and the second, for determining their resistance to high temperatures. For these variants, we incubated the seeds at the temperature of +24°C for an additional 8 hours or 30 minutes, respectively (the periods equal to the duration of applying SNT or HS in experimental variants). The seeds of experimental and control variants were then germinated in Petri dishes, 25 seeds each, in three repetitions, in the dark, at the temperature 25°C and air relative humidity 75-85%. The reaction of seeds of each wheat genotype to SNT or HS was judged by the percentage of seeds germinating within five days. After five days of incubation at +25°C, we mentioned that in control variants grew no less than 98% of the seeds. Therefore, the response of seeds to SNT or HS we judged directly based on the percentage of their germination in the experimental variants. Taking into account the reaction to HS of seeds reproduced in the Kharkiv region, from the list of genotypes mentioned above, we selected the following wheat genotypes for reproduction in 2017-2018 years in the Chisinau area: 466-2; 543-4; 111-5; 1108-6; Samurai- 13; Arctis-15; 857-29; 1087-37; Toulouse-45; 2146. Analysis of the reaction to HS and SNT of the seeds reproduced in the Republic of Moldova we performed with methods identical to those described above.

The average rate of seeds germination, standard deviation, and the mathematical expectation of the mean of the response of wheat gen o- types to SNT or HS was determined (Clewer et al., 2001; Penfield, 2017).

Results

Our preliminary research task was to determine the optimal parameters of SNT or HS doses, which would make it possible to separate wheat genotypes according to their primary resistance to extreme temperatures. In these studies, we used the seeds of Albidium and Odesskaya 267 varieties, respectively resistant to frost and high temperatures. Based on this research, we assessed the exposure doses to SNT or HS, application of which caused decreasing by about 50% of seeds germination of the varieties Albidium (after exposure to SNT) and Odesskaya 267 (after exposure to HS). These doses of the SNT, or HS, were obtained by incubating the seeds in the air thermostat at -7°C for 8 hours (SNT) or immersing them in water at +50°C for 30 minutes (HS). We applied the mentioned doses of extreme temperatures to seeds of the different wheat genotypes to assess their primary resistance to them.

The summary percent of fifty wheat genotypes seeds germination after exposure to SNT with -7^oC during 8 hours, or 30 min to HS with temperature +50°C, is presented in Figure 1. In this figure, we emphasize that there are presented the sums of the percentage of seeds germination after their exposure to SNT plus that of seeds germinated after exposure to HS. Thus, Fig. 1 expresses the distinct influence of SNT or HS and the additive values of their effect on genotype seed germination. Figure 1 data suggests the essential differences between genotypes regarding exposure to SNT or HS on seeds germination capacity. We emphasize that the numbers under each diagram correspond to the genotype numbering presented in the Materials and Methods section. Their sequence number increases with increasing resistance to SNT.

Fig. 1. The percentage of germinated seeds characteristic for 50 winter wheat genotypes expressed as the percentage sum of the seeds germinated after exposure for 8 hours negative temperature shock (NTS, -7°C) plus a percentage of those grown after exposure for 30 minutes HS (+50°C)

The numbers under diagrams correspond to the number of the line or variety described in the Materials and methods section. All theoretically possible values of the germination percentage of seeds representing different genotypes exposed to SNT and HS can occupy the range between 0 and 200%. Because the mentioned summary values mark the integral influence of the SNT and the HS on seed germination, this sum simultaneously marks each genotype's plasticity regarding seeds' response to the action of extreme temperatures (positives and negatives). Since in the control variants, seed germination for all genotypes practically has reached 100%, the values less than 200% of the sum of germination percentages represent the summary influence of the shock with extreme temperatures on seed germination. The lower this value is, the lower is the genotype resistance to shock with extreme temperatures (or plasticity). Simultaneously, the lower the percentage of seed germination after exposure to SNT or HS is, the lower is the primary resistance of the genotype to SNT or HS. To differentiate the genotypes after their plasticity, we have divided them into three groups in dependence of their summary response to exposition to SNT and HS: I - the genotypes with low plasticity - the summary seed germination rate did not exceed 100%; II - the genotypes with medium plasticity - the summary seed germination rate lay between 100 and 140%; III - the genotypes with high plasticity - the summary seed germination rate exceeded 140%.

The data included in Fig. 1 show that, according to the plasticity, the analyzed 50 wheat genotypes were divided into three groups containing 20, 18, and 12 genotypes, with low, medium, and high plasticity levels, respectively. The group of those 20 genotypes characterized with low plasticity includes one genotype with medium resistance to SNT (37 - line 1087), the resistance to SNT of all others genotypes was low. At the same time, the genotypes marked under the numbers 1, 5, 2, 9, 4, 10, 6, 3, 17, and 16 (namely genotypes 140, 111, 466, Batico, 542, Actor, 1108, 423, 1169, 300) had the medium resistance to HS, the other genotypes of this group had low resistance to HS. Genotypes from this group did not contain forms with high resistance to SNT or HS (to which the percentage of seed germination after exposure to SNT or HS would exceed 70%). Thus, in the mentioned group, nineteen genotypes demonstrated low resistance to SNT, and ten - low HS resistance. It follows that in this group genotypes showed a tendency to be more resistant to HS compared to SNT. The mentioned legitimacy was confirmed by the high level of the negative correlation coefficient between the percentage of seeds germination after exposure to HS and SNT, equal to -0,646.

The group of those 18 genotypes characterized with medium plasticity included nine genotypes, indicated under the number 32, 33, 38, 36, 40, 34, 30, 31, and 9 (genotypes 379, 1054, 634, 1014, 83, 29, Scajen, 48, 517), that demonstrated low resistance to SNT, the resistance to SNT of other nine genotypes was medium. Of this group, only the genotype with number 38 (line 634) was characterized with a low resistance to HS, the other 17 genotypes were of medium resistance. It is clear that the genotypes in this group, like those included in the group with low plasticity, also tended to be more resistant to HS than to SNT, the correlation coefficient regarding the resistance of genotypes to HS and SNT being also negative and equal to -0.627.

The expected and experimentally determined relative frequency (EF) of distribution of wheat genotypes in groups with low, medium, or high resistance to shock with negative temperature (SNT), heat shock (HS), or weighted average to both types of shock

Of the 12 wheat genotypes that made up the group with high plasticity, most showed increased resistance to SNT and, at the same time, to HS. The percentage of seeds germinated after exposure to SNT tended to be below 70% only for genotype below number 35 (line 87). After exposure to HS, a similar trend was characteristic for seeds of the genotypes indicated under numbers 48 and 50 (representing the Ovidii variety and line 1013). As a result, for the group of genotypes with high plasticity, the tendency of negative correlation between the resistance of genotypes to HS and SNT decreased considerably, the correlation coefficient reaching the value -0.133.

Fig. 1 shows a large variety of genotypes distribution according to the percentage of their seed germinated after their exposition to SNT, HS, and the summary percentage of those grown after SNT plus HS.

Quantitative data on the frequency of distribution of wheat genotypes in the groups with low, medium, or high resistance to SNT, HS, and the sum of the percentages of those germinated after SNT or HS are included in the Table. We mention that the theoretically expected rate of the number of genotypes that would fall into the group of genotypes with low resistance (germinated 0-50%), medium (germinated 50-70%), and high (germinated 70-100%) after exposure to shock with extreme temperatures should be equal to 0.5, 0.2, and 0.3, respectively. The summary interval of the percentages of germinated seeds after exposure to SNT or HS was doubled in each resistance group. These data suggest that the distribution of gen o- types by their primary resistance to extreme temperatures was not accidental. First, we notice that the rate of genotypes with a low resistance to HS was twice lower than that theoretically expected. But the rate of those with medium resistance, on the contrary, was practically twice as high. Second, when comparing the theoretical frequency of genotype distribution with low or medium resistance to SNT with the experimentally determined one, we observe that the latter of genotypes with low resistance tended to be higher. The one with medium resistance, on the contrary, was smaller. As expected, the summary response to HS and SNT, which generally characterizes the plasticity of genotypes, showed a clear trend of increasing the rate of genotypes with medium and high plasticity and decreasing those with low plasticity. In the group of those 50 genotypes included in the research, selection aimed to increase the resistance to high temperatures, which, ultimately, ensured the tendency to increase the number of genotypes with medium and high plasticity of response to extreme temperatures. The conclusion is confirmed by the number of genotypes with a low resistance to SNT is equal to 28 when the number of genotypes in the group of low plasticity is equal to 20. The mentioned above suggest that the selection of gen o- types for at least one resistance trait was successful. It is necessary to highlight that the only three genotypes (line 91, varieties Odesskaya 267 and Ovidii) concomitantly showed high primary resistance to HS and SNT. We cannot exclude that the selection of individual genotypes based on their adaptive potential and ability to avoid the influence of stress temperatures (Levitt, 1980; Lopes et al., 2010; Dascaliuc et al., 2013) could determine their passing through all processes of selection. In general, our results are consistent with the literature data, which indicates that the molecular and physiological processes that determine the resistance of plants to high temperatures and frost are mostly different (Levitt, 1980; Dascaliuc et al., 2013) and are of varying nature (Udovenko, 1988; Dascaliuc et al., 2013). These data support the view that during the selection of wheat genotypes, included in our research, attention was mainly paid to characteristics that assured their high resistance to extreme temperatures.

Fig. 2. The sum of the percentage of seeds germinated of the 10 winter wheat genotypes expressed as a percentage sum of the seeds germinated after exposure for 30 minutes heat shock (HS, +50°C) plus grown after exposure for 8 hours negative temperature shock (NTS, -7°C)

The data obtained with the seeds reproduced in Ukraine and Moldova is presented respectively on the left and right sides of the figure. The number under each diagram corresponds to the line or variety of wheat, indicated in the Materials and Methods section.

Fig. 2 shows the comparative data on plasticity of the response to HS and SNT of 10 winter wheat genotypes seeds reproduced in Ukraine and Moldova. For additional research, for multiplication in Moldova we chose 10 genotypes whose seeds after reproduction in Ukraine were characterized by a wide range of distribution of resistance to SNT (Fig. 1). The seeds of the genotypes indicated with the numbers 2, 4, 5, and 6, which represent the lines 466, 542, 111, and 1108, obtained from plants grown in Ukraine, were characterized by low resistance to SNT and medium resistance to HS, except for line 542, which demonstrated high resistance to HS. The seeds of genotypes indicated with the numbers 13 and 15, representing the varieties Samurai and Arctic, manifested concomitantly with a low resistance to SNT and HS. The genotypes with numbers 29 and 37, representing the lines 517 and 1087, were respectively characterized with a reduced and medium seed resistance to SNT, and high and low resistance to HS. The genotypes 45 and 46 (variety Tuluza and line 21) concomitantly demonstrated a high seed resistance to SNT and HS. As expected, their classification according to HS resistance has a different distribution from that which characterizes the resistance of genotypes to SNT (Fig. 2). The low value of the correlation coefficient (-0.058) between the resistance to SNT and HS characteristic for the seeds of the mentioned genotypes confirms this conclusion.

As the result of cultivation in Moldova, the seeds of all genotypes, except those of the variety Tuluza (with medium resistance to SNT), had low resistance to SNT. In contrast, except for genotype 46 (line 21), with a low resistance to HS, lines 542 and 111 - with medium resistance, and for the rest of the group's genotypes, it was characteristic high resistance to HS. Simultaneously, the seeds of genotypes 2, 13, 37, and 45 obtained from the plants grown in Moldova showed relatively high resistance to HS. The correlation coefficient between the resistance of genotypes to HS and SNT reached the value of 0.434, which is much higher than that characteristic for the seeds reproduced in Ukraine, mentioned earlier (-0.058). Suppose we determine the correlation coefficient of the resistance to SNT or HS of the seeds multiplied in Moldova and Ukraine. In that case, their values will be respectively equal to 0.481 and -0.314. These data show that, although, in general, the resistance to SNT of seeds reproduced in Moldova was lower compared to those of seeds obtained from the plants grown in Ukraine, the declining of the SNT resistance of seeds reproduced in Moldova tended to be in the same direction for all genotypes. The negative correlation coefficient between the HS resistance of the seeds propagated in Ukraine and Moldova suggests the opposite direction of the HS resistance modifications of the seeds obtained from the plants grown in Moldova compared to those reproduced in Ukraine. For example, the HS resistance of seeds of the genotypes indicated with numbers 4, 5, and 45 was higher for seeds reproduced in Ukraine, when that of the genotypes 13, 15, 37, on the contrary, was higher when seeds were reproduced in Moldova (Fig. 2). When analyze the level of plasticity of the response to temperature shock the seeds of wheat genotypes reproduced in Ukraine, we can mention that high plasticity was specific to seeds of the variety Tuluza, medium - to those of lines 21 and 517; the seeds of other genotypes have the low plasticity. The seeds of the Tuluza variety obtained from plants grown in Moldova had high plasticity too. In contrast, the plasticity of reaction to excessive temperatures of the seeds of nine other wheat genotypes was low.

Discussions

Considering that the difference of frost resistance between wheat varieties increases with the adaptation processes' accomplishment, the traditional methods of determining the frost resistance of wheat genotypes ordinarily are after performing the adaptation processes (Udovenko, 1988; Fowler et al., 2014). It was considered that the resolution power of methods for differentiating genotypes according to their level of frost resistance turns out to be the highest precisely when the plants are in an adapted state. However, we have to take into account that the long duration of accomplishing the adaptation processes and the specificity of the kinetics of these processes in the plants of different genotypes depends on the environmental conditions (Dascaliuc et al., 2013). These factors determine the high costs, low productivity of the methods, and the variability of the obtained results. Although the maximum difference between the primary frost resistance of wheat varieties practically does not exceed 3°C and that of adapted plants reaches 12°C (Fowler et al., 2014), the relative simplicity and reproducibility of the procedures for determining the primary frost resistance of seeds inspired us to test the resolving power of this method in more detail. Later we posed the problem of determining the primary resistance of wheat genotypes to high temperatures, which ultimately allowed appreciating the plasticity of the reaction of different wheat genotypes to the action of excessive temperatures (positive and negative). For this, it was necessary to eliminate the natural heterogeneity of the seed germination rate. It is determined by the genetic specificity, the conditions of seeds formation and maturation, and those of their germination (Blum, 1996; Dascaliuc et al., 2013). The germination control of the wheat seeds implies the equilibrium between opposite influences of plant hormones. Gibberellin produced in the embryo, whose transport in the aleuronic layer initiates mobilization carbon reserves stored in the endosperm compete with the inhibitory effects on their mobilization by the abscisic acid produced in the endosperm (Blum, 1996). During the preparation of the seeds for germination, they undergo a series of processes to repair the damages to the cellular structures during the seed's dissection and maturation, which increases during seeds soaking with water during the germination period (Blum, 1994; Blum, 1996; Dascaliuc et al., 2013). Water imbibition is also associated with activation the mobilization of the reserves from the endosperm, induction of the respiration, transcription, and translation processes (Blum, 1994; Dascaliuc et al., 2013), followed by expansion of embryo cells radicle emergence. In our research, the method of preparing seeds for germination ensured their synchronization in the stage of the roots' pre-emergence. The effectiveness of synchronization was manifested by the germination in the control variant of practically 100% of seeds during the first 24 hours of incubation under favorable conditions for germination. When seeds reach an equivalent physiological state, their reaction to HS or SNT mainly depends on the genetic specificity of the genotype.

Our research used the theoretical approaches for evaluating the stress resistance of technical systems (Jaligot et al., 2015). The applicability of these approaches for studying the primary plant's resistance to extreme temperatures (before the manifestation of adaptation processes) has repeatedly been confirmed in laboratory experiments. Compared to those based on determining the growth parameters of plants after applying the HS (Jelev, 2016), their evident simplicity is a great advantage. The fact that technical systems, as a rule, cannot adapt forced us to determine ways to avoid this phenomenon when determining the resistance of plants to extreme temperatures. Since the seeds were well prepared for germination but have not yet germinated, we avoided the contribution of ontogenetic adaptations. In this state, seeds represent a unique model to evaluate the primary resistance of wheat genotypes to the action of excessive temperatures. The proposed method ensures the avoidance of the influence on the resistance of adaptations induced in ontogenesis. Due to this, it allows the determination of the primary resistance of the genotype to extreme temperatures.

In conclusion, we emphasize that the proposed method of wheat genotypes distribution according to their primary resistance to extreme temperatures is in strict accordance with the accelerated methodology of testing the resistance the biosystems to stress factors (Escobar, 2006; Dascaliuc et al., 2013). Previously, we performed numerous experiments on selecting appropriate doses (temperature and duration of exposure) for accelerated testing of the primary resistance of wheat gen o- types to extreme temperatures. In the accelerated test, the plant exposure temperatures exceeded the natural ones, but the exposure doses were within the tolerance range of the genotypes. This statement is supported by the data in Fig. 1 and 2. The data given in these figures provide a qualitative and quantitative characterization of 50 wheat genotype resistance to high temperatures and frost. The parameters of stress factors were maintained, and the results of their impact on various wheat gen o- types were determined. After practical mastering, the method and data presented in this article were obtained within two months, indicating a significant acceleration of testing compared to most classical methods (Levitt, 1980; Udovenko, 1988). Once developed, the accelerated procedure is recommended for use whenever it appears to test resistance to extreme temperatures of genetically related material. With some minor additional research, the proposed method is also applicable for testing other plant species. Moreover, we apply this method's principles to quickly assess plants' adaptive potential and for screening promising biostimulators, influencing plant resistance to extreme temperatures (Dascaliuc et al., 2013; Jelev, 2016).

The data presented in this article results from one of the few attempts to evaluate the differences between the intrinsic resistances of wheat genotypes to HS or SNT action. They have obtained the result of analysis of the reaction to shock with excessive temperatures of the seeds before germination. The elaborated methods are fast and give the possibility to determine in parallel the resistance of the seeds of a large number of genotypes to HS or SNT. We mention that the resistance characteristics determined by us depend on genetic, biochemical, and physiological processes that characterize the response of wheat genotypes to the action of extreme temperatures. In our experiments, the reactions are not influenced by the complex mechanisms of avoiding the action of stressors, phenomena that have mainly been taken into account in the amelioration of wheat in recent decades (Lopes et al., 2010; Fowler et al., 2014). We consider that the assessment of the primary resistance of wheat genotypes offers new possibilities for determining its interference with other mechanisms of resistance of wheat genotypes to frost or heat. The data obtained demonstrate that seeds resistance to both types of temperature shock is specific for different wheat varieties and is influenced by seed reproduction conditions. Due to this adaptive variability of genetic and epigenetic nature, wheat varieties and their descendants are characterized by high resistance and productivity in very different environmental conditions. The possibility of epigenetic inheritance suggests that it may influence the primary frost or heat resistance of wheat embryos. The data obtained by us demonstrate that their level of influence can probably be different depending on the conditions of seed reproduction (Fig. 2). Because meteorological conditions vary from year to year, they can influence the primary resistance of genotypes to heat stress factors even when reproduced in the same zone. Recently we obtained data showing that the distribution of seeds of wheat genotypes based on primary resistance to extreme temperatures does not change after seed storage for one year. Simultaneously, the data showed that the distribution of genotypes after the primary resistance to extreme temperatures varies when testing seeds were reproduced in different years.

Conclusions

Wheat varieties can be differentiated in accelerated mode after their primary resistance to extreme temperatures (excluding the influence of the adaptation processes carried out during plant ontogenesis) by exposing to HS or SNT of the seeds well-prepared for germination.

Resistance of different wheat genotypes seeds to HS or SNT can vary, being influenced by the environmental conditions of their reproduction.

References

1. Alexandrov V.Ya., Kislyuk I.M. 1994. Cell response to the heat-shock: physiological aspect. Cytology. 36 (1): 5-59. (In Russian).

2. Zhuchenko A.A. 1988. The adaptive potential of cultivated plants: genetic and ecological bases. Publisher. Kishinev. Shtiintsa: 267 p. (In Russian).

3. Ivanov V.B. 2003. The problem of stem cells in plants. Russian Journal of Developmental Biology. 34 (4): 205-212.

4. Udovenko G.V. 1988. Methodological guidance. Diagnosis of plants' resistance to stress. VIR, 228 p. (In Russian).

5. Jelev N. 2016. Diminishing the impact of abiotic stressors on Triticum aestivum L. plants by using the natural growth regulator Reglalg. Bulletin of the Academy of Sciences of Moldova. Life sciences. 3 (330): 72-79. (In Romanian).

6. Blum A. 1996. Crop responses to drought and the interpretation of adaptation. Plant Growth Regul. 20: 135-148.

7. Blum A. 1994. Stress tolerance in plants: what are we looking for? In: NATO ASI Series (Series H: Cell Biology). Springer, Berlin, Heidelberg. 86: 315324.

8. Clewer A.G., Scarisbrick D.H. 2001. Practical statistics and experimental design for plant crop science. Chichester, New York, 332 p.

9. Penfield S. 2017. Seed dormancy and germination. Curr. Biol. 27 (17): R874-R878.

10. Dascaliuc A., Ivanova R., Arpentin Gh. 2013. Systemic approach in determining the role of bioactive compounds. In: Bioactive Compounds from Natural Sources for Prophylaxis and Treatment of the Effects of Radiological, Chemical and Biological Agents NATO. Science for Peace and Security Series A: Chemistry and Biology book series (NAPSA): 121-131.

11. Escobar L.A., Meeker W.Q. 2006. A Review of Accelerated Test Models. Statistical Science. 21 (4): 552577.

12. Fowler D. Byrns B.M., Greer K.J. 2014. Overwinter Low-Temperature Responses of Cereals: Analyses and Simulation. Crop Sci. 54: 2395-2405.

13. Jaligot E., Rival A. 2015. Applying epigenetics in plant breeding: balancing genome stability and phenotypic plasticity. In: Advances in Plant Breeding Strategies: Breeding, Biotechnology, and Molecular Tools. 1: 159-192.

14. Levitt J. 1980. Responses of plant to environmental stresses. New York, 568 р.

15. Lopes M.S., Rebetzke G.J., Reynolds M.P. 2014. Integration of phenotyping and genetic platforms for a better understanding of wheat performance under drought. J. Exp. Bot. 659 (21): 6167-6177.

16. Lopes M.S., Reynolds M.P. 2010. Partitioning of assimilates to deeper roots is associated with cooler canopies and increased yield under drought in wheat. Funct. Plant Biol. 37: 147-156.

17. Novoseltsev V.I., Tarasov B.V., Golikov V.K., Demin B.E. 2006. Theoretical bases of the system analysis. Moscow, 592 p. (In Russian).

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