Fagopyrum esculentum Moench plants’ photosynthetic activity correlation with efficient grading factors

. About 95% of dry matter of agricultural crops is known to be provided by photosynthesis of plants. At the same time, its potential is realized by less than half: the efficiency of use of PAR by crops is usually in the range of 0.9 -1.5%, at best it reaches 2%. Obviously, activation of photosynthetic activity of plants by means of breeding can be considered as one of the promising ways to increase crop yields. This task is also relevant for buckwheat, which is a demanded food crop in the world market. In this regard, the purpose of the research was to study the possibility of using in buckwheat breeding the indicators of photosynthetic activity of plants based on their relationship with useful - economic characteristics of the variety. The results of the correlation analysis showed that the indicators of photosynthetic activity of buckwheat plants have a significant impact on the formation of the variety yield. Significant relationship of cultivar yield was revealed with leaf area (r=0.71), water use efficiency (r=0.68), photosynthetic potential (r=0.66) and photosynthetic intensity (r=0.35). Similar character of interrelation of these indicators in crop varieties was traced with harvesting index. It was found that the relationship between the structural and functional indicators of the leaf system of plants and the yield of buckwheat varieties does not remain constant, and significantly changes during the growing season of plants. The high polymorphism of the crop gene pool in terms of photosynthetic activity of plants and their significant relationship with the yield of the variety indicate the possibility of targeted breeding work in this direction.


Introduction
It is known that the process of photosynthesis provides the formation of about 95% of dry matter of agricultural crops [1].However, its potential is realized by breeding, so far, to a weak extent.The efficiency of photosynthetic active radiation by modern agrocenoses of cultivated plants is usually within 0.9 -1.5%, at best it reaches 2.4% in C3 and 3.4% in C4 plants [2,3], whereas the upper limit of their photosynthetic efficiency may amount to 4.6% and 6.0%, respectively [4,5].
Therefore, many scientists consider the activation of photosynthetic activity of plants through breeding methods as one of the priority ways to further increase crop yield [6,7].This task is also relevant for buckwheat breeding, which is one of the demanded food crops on the agri-food market, especially in Russia, China, Canada, etc. [8,9].
In view of the above, we conducted studies on a large set of buckwheat genotypes, reflecting the period of crop breeding from local samples to the best modern varieties in order to identify the relationship of photosynthetic activity indicators with economically useful plant traits and to establish the possibility of their use in breeding.The presented scientific article is devoted to the obtained results.

Materials and Methods
The studies were carried out on the material and technical base of the Orel State Agrarian University "Genetic resources of plants and their use" in the framework of scientific cooperation with the breeders of FSBSI FSC legume and cereal crops.
Seeding was carried out by selection seeder SKS-6-10 in a row method with the rate of seeding 3 mln.pcs. of seeds per hectare.Plot area was 10 m2, placement was systematic with offset, 4-fold repetition.
Weather conditions of plant growth and development in the years of study were contrasting.Meteorological conditions in 2011 and 2013 were unfavorable for buckwheatin some periods they had a stressful nature for the crop.In 2011, the sum of precipitation during the growing season was 77.4% of the average annual norm, and the average monthly air temperature was higher by 2.4°C.In 2013 hot and dry period was mainly generative period of plant development, which was characterized by significant reduction of precipitation share (on average by 44.3%) relative to the multi-year value with average air temperature of 18.9 0 С.
The most favorable for growth and development of heat-and moisture-loving buckwheat crop were weather conditions of vegetation in 2014 and 2015.
In the experiments the following records were carried out: 1. photosynthesis intensity (PI), transpiration intensity (TI) and stomatal conductance (SC) were determined under field conditions on intact plants in real time using portable gas analyzer brand Li -6400 HT according to the original method of the company Li-COR.The sample consisted of 5 typical plants growing in the middle of the plot.Measurements were taken at the main growth phases and during the light period of a day on the lower leaf blades of 3...4 leaves from the top of the main stem of the plant; 5-fold repetition.
2. Water use efficiency (WUE) was calculated as the ratio of photosynthesis intensity to transpiration intensity, based on the methodical recommendations [10].
3. Leaf area was calculated by weight method.For this purpose, for each variety in 3fold repetition in 10 typical plants, first we counted the crude weight of the leaves and the area of 5 grams, which was determined on a LI 3000 C photoplanimeter of the American company LI-COR.And then, by the proportion method, the area of all leaves per plant was calculated.
4. Specific surface density of leaves (SSD, mg/dm 2 ) was determined by the ratio of the dry weight of leaf cuttings to their area.For this purpose, two lower leaf laminae on 3...4 leaves from the top of the plant were taken.Clippings were obtained from the middle part of the plate, avoiding developed veins.Weighing of wet and dry weight was carried out on analytical scales of BK -300.Repeatability by grade 3-fold.
5. Photosynthetic potential (PP) and net photosynthetic productivity (NPP) were studied according to the methodical instructions of A.A. Nichiporovich and co-workers [11].
6. Yield and its structural elements were determined from 10 plants by methods generally accepted in breeding, repetition for each variety 4 times.
7. The amount of accumulated dry matter by above-ground organs of plants was counted by taking plant samples of 10 plants from each plot of the variety, followed by drying at 105 o C in a drying cabinet brand SM 50/250-1000 SHS with the repetition of 3 times.
8. The harvesting index was calculated by the ratio of seed weight of the standard moisture content to the total dry weight of the plant and expressed as a percentage.
Mathematical processing of the experimental data was carried out using modern computer programs and taking into account the methodical recommendations of B.A. Dospekhov [12].

Results and Discussion
The results of the correlation analysis showed that the relationship of cultivar yield with structural and functional indicators of photosynthetic system of buckwheat plants is different in both significance and nature.It is most closely and positively related to leaf area (r=0.71),photosynthetic potential (r=0.66),water use efficiency (r=0.68) and photosynthetic rate (r=0.35).Whereas the intensity of leaf transpiration has no such effect on the final grain yield of the crop (Fig. 1).
This confirms the earlier conclusion that the photosynthetic activity of buckwheat plants, is one of the important factors in the formation of yield by the variety [13].It was shown that during the breeding period from local populations to the best modern varieties in plants increased: leaf area, on average, by 21.8%; photosynthetic potential, by 20.3%; and leaf photosynthetic intensity, by 24.7% [14].
Fig. 1.Relationship between structural and functional parameters of the photosynthetic system of plants ("blossoming+20 days" phase) and the yield of buckwheat varieties.
In many respects similar correlations of structural and functional indicators of the leaf system of buckwheat plants were shown with the harvesting index.The correlation in this case was positive and was as follows: with photosynthetic potential 0.53; leaf area 0.64; water use efficiency 0.66; photosynthetic intensity 0.33.The relationship between transpiration rate and harvesting index was negative (Fig. 2).

Fig. 2. Relationship between structural and functional indicators of photosynthetic system of plants ("blossoming+20 days" phase) and harvesting index in buckwheat varieties.
The mentioned correlations to a certain extent reflect the biological essence of the universal mechanism of yield increase in new varieties due to the harvesting index in breeding not only buckwheat [15], but also in other crops [16,17].Therefore, many scientists recommend using this index in the selection of forms with increased photoactivity and yield [18].
It was shown that the relationship between photosynthetic activity of buckwheat plants and the yield of the variety during the growing season does not remain constant, but changes with the transition of plants from one phase of growth to another.The correlation coefficient between yield and leaf area of the variety ranged from 0.21 to 0.71 during the growing season; with photosynthetic potential (PP), from 0.32 to 0.69; with photosynthetic intensity, from (-0.24) to 0.35; with stomatal conductivity, from (-0.24) to 0.79 (Table 1).The most significant correlation between the marked indicators was manifested in the period of seed formation and ripening, when the demand for photoassimilates significantly increased [14].
A close relationship of structural and functional parameters of the leaves of plants was also noted with the number and weight of 1000 seeds in the variety ( At the same time, the influence of leaf transpiration activity on the elements of the variety yield structure was not significant.This is despite the fact that leaf transpiration provides an uninterrupted supply of mineral nutrition elements and water from the soil to the above-ground organs, protecting their cells from overheating and dehydration [19,20].The most probable reason for this is high energy expenditure [21], from which K.A. Timiryazev considered plant transpiration as a "necessary evil", which cannot be avoided, but should be strived to reduce to the necessary size.

Conclusion
Thus, the activation of photosynthetic activity of buckwheat plants by means of breeding should be considered as one of its promising areas.The positive reliable correlation between grain yield and leaf area (r=0.71),water use efficiency (r=0.68),photosynthetic potential (r=0.66),stomatal conductance (0.79) and photosynthetic activity (r=0.35) was established in the cultivars.This relationship in buckwheat varieties does not remain constant but changes significantly during the growing season.The high polymorphism of the gene pool of the crop in terms of photosynthetic activity of plants and their significant relationship with the yield of the variety indicate the possibility of effective targeted work in this direction.It should be taken into account that photosynthesis is a complex in organization and functioning interconnected system with complex inheritance.Improvement of photosynthetic efficiency by means of one factor is unreasonable since knowledge about biological systems at cellular or molecular level can't predict all properties of the whole plant, as well as peculiarities of agrophytocenosis functioning can't be predicted based on peculiarities of functioning of individual plants, because with transition from lower level of biological system organization to higher level new additional properties appear which are inherent only to a given stage Optimization of all components of the photosynthetic system is necessary.Combination of traditional breeding methods with modern innovative methods, including modeling and genetic engineering technologies, has the greatest prospects in this case to solve the task of increasing the activity and efficiency of photosynthesis.
The research was carried out with the support of a grant from the Russian Science Foundation under Project No. 22-26-00041, https://rscf.ru/project/22-26-00041/

Table 1 .
Value of correlation coefficients (r) between variety yield and structural and functional parameters of buckwheat leaves in different periods of vegetation.Reliably at Р<0.05.

Table 2 .
Value of correlation coefficients (r) between structural and functional indices of leaves (phase "blossoming+20 days") plant productivity and elements of yield structure in buckwheat varieties.Reliably at P<0.05.