The influence of fungicides on the growth, development and productivity of soybean

. The paper presents the results of a two-year experiment on fungicide Deposit, muE (1.0 l/t and 1.2 l/t) and its combinations with fungicide Optimo, EC (0.5 l/ha). The experiment was conducted in the south of the Russian Far East in 2021-2022. The first step was a phytophathological inspection of the seeds treated with the fungicide in the laboratory conditions. Deposit was noted to have an antibacterial and antifungal effect. A rhizotron was used for further experimental work to observe the growth and development of soybean plants. It was established that Deposit did not have a negative effect on the crop and facilitated a slight increase in plant weight. The last step of the research was field plot experiments aimed at studying the efficacy of the fungicides against root rot and leaf and stalk diseases of soybean. Deposit was observed to inhibit root rots damaging the crop. At the stage BBCH 62, the fungicide decreased the intensity of infection progression by 11.0% (1.0 l/t) and 15.6% (1.2 l/t). Deposit and Optimo had a high antipathogenic activity against leaf and stalk diseases of soybean. It was established that the fungicides and their combinations were effective against Septoria blight (22.1-35.5%), Cercospora leaf blight (29.7-70.4%), and Ascochyta blight (20.4-58.4%). Additionally, they increased the thousand kernel weight (TKW) and soybean yield.


Introduction
Soybean is a crop in an ever-increasing demand.Despite a high cost of its production, more and more farmers begin to grow the crop and expand the land area under its cultivation [1].The main regions of soybean production in Russia are Amur oblast, Primorsky and Krasnodarsky kray, and Kursk and Belgorod oblast.They account for 62% of the total land area under soybean cultivation in the country [2].
Soybean is one of the most valuable crops in the world for its products are used in various sectors of economy (automotive, paint and varnish, and food industries).Soybean seeds contain enzymes and inhibitors that have curative properties against cancers.Involving soybean in crop rotations can enhance the fertility of soil [3].
However, susceptibility to dangerous diseases is a factor that seriously limits the yield of soybean globally [4][5][6].
The damage caused by various diseases is determined by environmental conditions, the biology and distribution of a pathogen as well as the characteristics of seed material.These diseases can severely impair different parts of plants, including seeds, shoots, roots, leaves, and pods.Plant roots take in water and nutrients into the plant body and, therefore, they are essential components of the total plant productivity [7].Well-developed and functional roots are key to the survival of plants and the achievement of high yield [8].
Studying roots under field conditions is a difficult task, which still relies on traditional methods such as manual measurements and visual evaluation.Such methods have some disadvantages, e.g. it is impossible to study the dynamics of the development of individual plants and there is always a possibility of extracting a plant from soil in an incomplete form.To overcome these limitations, several laboratories experimented with methods for obtaining information on the structure and functions of the plant roots grown in natural substrates such as transparent columns filled with soil or rhizotrons [9][10][11].Observing roots at the transparent borders of the horizon is one of the earliest non-invasive methods for studying the growth of roots in soil, which was carried out for the first time in the 19th century [12].The shape and volume of rhizotrons depend on the research goal and might vary from small boxes to large containers, underground basements and lines fencing off natural soil profiles in field conditions to allow the direct observation of tree roots [13][14].An undisputable advantage of rhizotrons is a possibility of conducting recurrent measurements of the same roots at short intervals [12].Such devises allow researchers to record any slight changes in the growth and development of experimental crops and to register the infection in root system at early growth stages.
All soybean diseases can be divided in three big groups: 1) diseases of seeds and seedlings, 2) spots covering different plant parts, and 3) diseases causing the withering of plants [15].The total yield loss due to fungal diseases can be up to 40% [6].
Airborne seed infections are the most dangerous, e.g.downy mildew, Septoria blight, bacteriosis, and Cercospora blight, which adapted to use seeds as an additional ecological niche and can be transmitted in the course of sowing year after year [16].
Seed treatment with fungicides is one of the most effective modern methods for reducing the harmfulness of plant diseases [17].
Pre-sowing treatment of seeds has a number of economic and organizational advantages such as low cost and efficacy irrespective of weather conditions.It should be noted that fungicidal treatment allows the protection of seed material at the earliest stages of plant development.Root and stem rot caused by pathogenic fungi severely damage the crop.The damaged plants suffer from decreased germination and growth failure; their stems wither prematurely leading to the death of plants at early developmental stages.
Fungicidal seed treatments are effective enough at the initial growth stages -from the emergence of seedlings to the beginning of flowering (BBCH 10 -BBCH 60).Later their effect significantly reduces [18].In this case, support can be provided by fungicides aimed at protecting growing plants.A complex strategy is required to protect plants from the moment of germination to the end of the growing season.
The research goal was to study the efficacy of fungicide Deposit at different application rates under laboratory and field conditions and the synergistic effect of a complex treatment with fungicide Optima against the main fungal pathogens of soybean as well as the influence of these fungicides on the crop in general.
The research was conducted at the Far Eastern Scientific Research Institute of Plant Protection -branch of the Federal Scientific Center of Agricultural Biotechnology of the Far East named after A.K. Chaiki in 2021-2022.Firstly, a phytopathological inspection of seeds was carried out under laboratory conditions according to State Standard (GOST) 12044-93 [19].Secondly, it was studied how fungicide Deposit (1.0 and 1.2 l/t) influenced the development of the root system and above ground parts of soybean plants.The dynamics of plant growth was studied using a rhizotron.The method is based on the cultivation of plants in rhizotrons and recurrent measurements of changes in the roots and above ground parts of each individual plant.This principle allowed us to observe how the plants grew from the cotyledon stage (2 cm root) to the stage V(n).Potting mix with soil and humus (1:2) was used as a substrate.The prepared substrate was sifted through a mesh with cells 3-5 mm in diameter and then moistened at a ratio of 16 kg of the prepared substrate : 2-2.5 l of water.A rhizotron was filled with the substrate in small portions (approximately one liter) so the potting mix would be evenly distributed along the full length.The lower layers were compacted and differed in density from the uppermost layer (2-3 cm).After the rhizotron was fully filled, it was shaken and a necessary amount of the substrate was added to a height of 6 cm below the upper edge.The uppermost layer of the substrate was compacted with a tamper.Seeds (10 pcs.) were placed along the glass wall (embryo towards the glass) with forceps.The distance between the glass and embryo was ≤ 5 mm.The seeds were covered with a 2 cm layer of the substrate, which was then compacted with the tamper.Compacting the substrate allowed a better contact between the soil and seeds and therefore a more successful germination.The seeds placed in the soil was not watered.Initial watering might be necessary only for shallowly embedded seeds of vegetable crops.To preserve the initial humidity and to create an incubation chamber, the rhizotron were tightly closed with plastic lids until the emergence of seedlings.The rhizotrons were fixated at a 30° angle to optimize the growth of plant roots along the glass wall.The glass of the rhizotrons was covered with a blackout fabric.The environmental conditions were as follows: 12 h photoperiod (from 8 am to 8 pm local time), daytime/ nighttime temperature of ~25/22ºС, and additional lighting provided by Philips HPI-T Plus 250W/645, SPB-Т8-FITO 12W 230V IP40).
The dynamics of root growth and development were studied by measuring the length of visible roots from the point of planting to the root tip with a ruler every third day.One of the main advantages of rhizotrons is an opportunity for analyzing root systems without the extraction of plants from soil.
Lastly, an experiment was conducted to evaluate the efficacy of the fungicides against fungal pathogens of soybean under field conditions.The soil of the experimental plot was meadow brown bleached and moderately loamy soil.The content of humus was 3.8%; the pH of the soil solution was slightly acidic (рН 5.3).
The soil was prepared according to the agricultural technology accepted in Primorsky kray -autumn ploughing at a depth of 18-20 cm, harrowing in early spring followed by tillage (two times).The seeds were sown in single rows at 45 cm row spacing.The area of one experimental plot was 10.8 m 2 (1.8 m х 6 m).The experiment was conducted with four repetitions; the positioning of experimental variants was randomized.Seeds of soybean variety Asuka were sown at a rate of 100 kg/ha.The predecessor was also soybean.No fertilizers were applied.The seeds were treated with the fungicide by a semi-dry method before planting.The experimental plan included the control without any treatment; Deposit, muE (the active ingredient was imazalil 40 g/l + metalaxyl 30 g/l + fludioxonil 40 g/l), at a rate of 1.0 l/t; Deposit, , at a rate of 1.2 l/t; Optimo, EC (pyraclostrobin 200 g/l), at a rate of 0.5 l/ha; Deposit, muE, at a rate of 1.0 l/t + Optimo, EC, at a rate of 0.5 l/ha; and Deposit, muE, at a rate of 1.2 l/t + Optimo, EC, at a rate of 0.5 l/ha.Fungicide Optimo was applied at the stage BBCH 51 during the growing period.To control weeds, herbicide Fabian, WDG, was used (imazethapyr 450 g/kg + chlorimuron-ethyl 150 g/kg) as well as manual weeding during the growing period of soybean.Commonly accepted methodology was employed for making field and laboratory records and conducting scientific observations of the growth and development of soybean plants [20][21][22].
The statistical processing of research results was performed by the method of one-way ANOVA according to the "Methodology of field experiment", 1985, by B.A. Dospekhov [23].

Results and discusion
The conducted phytopathological analysis of the seed material showed that the seeds were severely damaged by Fusarium (a pathogen of root rot) and bacteriosis.Figure 1 demonstrates that the seeds treated with the studied fungicide had a lower infection rate and thus were more resistant to the primary infection in soil.

Fig. 1. Phytopathological inspection of soybean seeds
The inspection revealed that the studied fungicide facilitated a slight increase (t05Sd = 5.3%) in the germination rate of seeds by 3% (Deposit 1.0 l/t) and by 2% (Deposit 1.2 l/t).The germination rate was 95% in the control variant.
The laboratory experiment with the rhizotrons allowed us to obtain images of plants showing the dynamics of soybean growth and development (Table 1).The research determined that the studied fungicide did not have an adverse effect on the root system of soybean plants.There was only a slight difference in the root length between the three variants (Figure 2).Deposit slowed down the growth of the above ground plant parts at both application rates.The difference in the plant height between the control and the experimental variant with the highest amount of the fungicide became insignificant only by the stage BBCH 13.The weighting of plants showed there was a tendency towards an increase in plant weight (by 0.41 g) in the variant with Deposit application at a rate of 1.2 l/t compared to the control (t05Sd = 0.54).Plant samples were collected in the field conditions to evaluate the degree of the damage caused by root rots.The research results proved that the use of Deposit at different application rates significantly decreased the intensity of pathogen development in the crops.Figure 3 demonstrates typical spots of root rot at the root crown of the plants in the control variant while there were no such lesions in the variant with the fungicide application.

Control
Deposit, 1.0 l/t Deposit, 1.2 l/t Based on Figure 4, it can be concluded that the studied fungicide had a positive effect on soybean plants at both application rates.The biological efficacy of Deposit applied at the minimum rate was 34.8% at the stage BBCH 12 but decreased by 13.1% at the stage BBCH 62.The application of Deposit at a rate of 1.2 l/t was less effective at the stage BBCH 12 compared to the lowest application rate but preserved a high efficacy at the stage BBCH 63.
The first symptoms of soybean leaf and stem diseases were noted in the first ten-day period of June (stage BBCH 15).Pathogens reached their maximum potential by the end of August (stage BBCH 75).The following leaf diseases were detected: Septoria blight (Septoria glycines Hemmi), Cercospora leaf blight (Cercospora sojina Hara), and Ascochyta blight (Ascochyta sojaecola Abramov).Septoria blight was the first one to appear on the primordial leaves of soybean plants by the stage BBCH parameter that fully reflects the character of disease progression during the growing period -was 468.7 (biological efficacy was 35.5%) in the variant with the complex treatment with Deposit (1.2 l/t) and Optimo and 726.8 in the control variant.The higher the AUDPC, the greater the degree of the damage caused by the pathogen (Figure 5).The conditions during the years of our experiment were favorable for the development of Cercospora blight.The disease was detected by the stage BBCH 60.The highest efficacy was observed in the variants with the complex treatment (70.2-70.4%);Optimo was noted to be less effective (61.8%).During the growing period, Ascochyta blight manifested itself in typical isolated spots.The use of the studied fungicide at the minimum rate was ineffective against the pathogen.The complex treatment with Deposit and Optimo facilitated a decrease in the disease development by 58.4% (Figure 5).
It well known that yield depends on many parameters, among which the characteristics of commercial yield structure.The use of the studied products was observed to increase the TKW.In all experimental variants, the TKW was confidently higher than in the control (173.93 g) by 4.94-12.01g (t05Sd = 5.14 g) (Figure 6).The correlation analysis of the research results revealed a strong negative correlation between the intensity of fungal infections and the yield of soybean (r = from -0.63 to -0.86).Thus, the higher the degree of disease development, the lower the productivity of the crop.The control variant had the lowest yield (2.17 t/ha) compared to the variants with the seed treatment and fungicide use, which inhibited the disease development.The studied products and their combinations facilitated an increase in the yield of soybean.Using Deposit at the minimum rate resulted in a modest yield gain of 0.25 t/ha.All other experimental variants were characterized by a confident gain compared to the control 0.40-0.58t/ha (t05Sd = 0.35 t/ha).

Conclusions
The phytopathological inspection of the seeds treated with Deposit at a different application rate showed that the fungicide had an antibacterial and antifungal effect and decreased the amount of infection in the seed material.Analyzing the experimental data obtained using the rhizotrons proved that Deposit did not have a retardant effect on the crop.The two-year experiments on the combinations of Deposit and Optimo revealed that the pre-sowing treatment of seeds was an effective method for protecting plants against root rot and leaf spots under the conditions of the south of the Russian Far East at the early stages of soybean development.Using Optimo during the growing period facilitated the plant protection in the long run.The synergetic effect of the two fungicides allowed a significant reduction in the pathogen development as well as an increase in the TKW and soybean yield.

Fig. 4 .
Fig. 4. Intensity of the development of root rot and the biological efficacy of Deposit (the average for 2021 and 2022)

Fig. 5 .
Fig. 5. Biological efficacy of the fungicides against leaf and stalk diseases of soybean and the AUDPC (the average for 2021 and 2022)

Table 1 .
Dynamics of the growth and development of soybean plants E3S Web of Conferences 431, 01062 (2023) ITSE-2023 https://doi.org/10.1051/e3sconf/202343101062 E3S Web of Conferences 431, 01062 (2023) ITSE-2023 https://doi.org/10.1051/e3sconf/202343101062Fig. 2. Influence of fungicide Deposit on the growth and development of soybean plants (Аdynamics of the development of above ground parts; В -dynamics of the development of root system; С -plant weight at the last recording) Yield and thousand kernel weight of soybean plants (the average for 2021 and 2022)