Method for improving heat resistance of soybeans in flowering phase

Abstract

The invention belongs to the technical field of plant growth, and particularly relates to a method for improving the heat resistance of soybeans in the flowering phase. The method comprises the following steps: after a first flower of an initial flower node of a soybean stem blooms, applying a naphthylacetic acid solution to an inflorescence of the initial flower node of the soybean stem under high temperature stress so as to relieve high-temperature heat damage in the flowering phase of soybean plants; the application amount of the naphthylacetic acid solution is 45L / mu to 55L / mu. The method provided by the invention has a good effect of relieving high-temperature heat damage in the soybean flowering phase, and is simple and easy to implement. The method has the effects of remarkably relieving the inhibition of high temperature in the flowering phase on seed development, improving the flower and pod protection rate and not influencing the biomass of the overground part, and has potential application and research values in the aspect of dealing with disaster and yield reduction caused by high temperature in the flowering phase of soybeans.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of plant growth, and particularly relates to a method for improving heat tolerance of soybean in flowering period. BACKGROUND

[0002] Soybean originated in China. Research shows that the key problem currently limiting the increase of soybean yield per mu is the lack of grains per plant caused by flower and pod shedding. In particular, with the intensification of factors such as climate warming, extreme high-temperature weather occurs frequently, and high temperature (greater than 26 o C) has become an important factor restricting the increase of soybean yield per mu. Research shows that the average temperature in the soybean growing season can reduce production by 3.1% per 1°C increase, and the reproductive growth is more sensitive to adverse environment than the vegetative growth. Global climate warming leads to high overlap between soybean flowering period and summer high temperature, which aggravates flower and pod shedding and becomes a key factor restricting the increase of soybean yield. The initial flowering period of soybean includes key processes such as fertilization, zygote division and proembryo development. This stage not only marks the beginning of seed development, but also directly lays the early foundation for the final yield. Ensuring soybean seed development after initial flowering under high temperature stress plays a decisive role in the potential yield of soybean.

[0003] However, the method for improving high temperature stress of soybean is to apply a soybean flower and pod retention plant growth regulator, but the application effect of the method is limited, and the regulation effect on high temperature stress is not clear. SUMMARY

[0004] To solve the problems of the method for improving high temperature stress of soybean in the prior art that the application effect is limited and the regulation effect on high temperature stress is not clear, the application provides a method for improving heat tolerance of soybean in flowering period. The method is to take the initial flowering node of the main stem of soybean as an example, and to apply or spray naphthalene acetic acid solution to the inflorescence of the initial flowering node of the main stem of soybean under high temperature stress after initial flowering of soybean, so as to ensure seed development, improve flower and pod retention, and reduce the risk of yield reduction caused by high temperature. To achieve the above purpose, the application adopts the following technical scheme.

[0005] The application provides a method for improving heat tolerance of soybean in flowering period, which comprises the following steps: After the first flower of the initial flowering node of the main stem of soybean opens, naphthalene acetic acid solution is applied to the inflorescence of the initial flowering node of the main stem of soybean under high temperature stress, so as to alleviate the high temperature damage of soybean plants in the flowering period.

[0006] The application amount of the naphthalene acetic acid solution is 45L / mu to 55L / mu.

[0007] Under different cultivation conditions in the greenhouse and in the field, the application sprays or applies a low-concentration naphthaleneacetic acid (auxin analogue) solution to the inflorescence of the first flower of the main stem of a soybean plant under high-temperature stress after the first flower of the main stem of the soybean plant opens, and investigates the pod development process of the main inflorescence of the first flower node, the seed integument and embryo development status and cell number of the first flower node, the flower and pod retention rate of the first flower node, and the effective pod number, effective grain number and effective grain weight of the first flower node, to determine that, under high-temperature stress, spraying or applying a low-concentration naphthaleneacetic acid solution can significantly alleviate the inhibition of high temperature on the seed development process, promote the normal development of the seed integument and embryo, increase the flower and pod retention rate, and increase the effective pod number and yield per plant. The application not only provides an effective agronomic control method for relieving high-temperature stress after the first flower of a soybean plant opens, but also explains the action mechanism from the physiological aspect of seed development, thereby providing an implementable technical solution and a corresponding theoretical basis for solving the problem that the application effect of the method for improving high-temperature stress of a soybean plant in the prior art is limited and the regulation effect on high-temperature stress is not clear.

[0008] Preferably, the concentration of the naphthaleneacetic acid solution is 0.08 nM to 0.12 nM.

[0009] Preferably, the naphthaleneacetic acid solution is prepared by a step-by-step dilution method using naphthaleneacetic acid as a raw material.

[0010] More preferably, the naphthaleneacetic acid solution is prepared as follows: First, naphthaleneacetic acid is dissolved in a 0.1M NaOH solution, and the volume is adjusted to prepare a 1mM stock solution; then, the solution is diluted step by step, and the dilution ratio of each step is 1000 times, and 1M and 1nM dilution solutions are obtained in sequence. After adjusting the pH of the obtained solution to 6.5, the solution is further diluted by 10 times to obtain a 0.1nM working solution.

[0011] Preferably, the naphthaleneacetic acid solution is sprayed or applied.

[0012] Preferably, the naphthaleneacetic acid solution is applied on the day when the first flower of the main stem of the soybean plant opens.

[0013] Preferably, improving the heat tolerance of the soybean plant during flowering includes increasing the effective pod number, effective grain number and effective grain weight of the main stem of the soybean plant under high-temperature stress.

[0014] Preferably, improving the heat tolerance of the soybean plant during flowering includes promoting the pod development process of the main stem of the soybean plant under high-temperature stress.

[0015] Preferably, improving the heat tolerance of the soybean plant during flowering includes increasing the size and cell number of the seed integument and embryo in the pod of the main stem of the soybean plant under high-temperature stress.

[0016] Preferably, the soybean plant is Zihuang 34.

[0017] Compared with the prior art, the present application has the following beneficial effects: 1. The present application provides a method for improving the heat tolerance of soybean during flowering. The method provided by the present application includes exogenous application of a low-concentration naphthaleneacetic acid (auxin analogue) solution to the inflorescence of the main stem of the soybean plant after flowering to alleviate the high-temperature heat damage during flowering of the soybean plant. The application amount of the auxin analogue naphthaleneacetic acid solution is 45L / acre to 55L / acre. The present application uses a single auxin analogue naphthaleneacetic acid to be accurately applied at a critical node after flowering to promote seed development under high-temperature stress, thereby fundamentally solving the technical defects of the prior art that rely on multiple plant hormones and the unclear regulation effect of high temperature. Specifically, the existing complex regulator has a complex synergistic / antagonistic relationship between plant hormone components, resulting in a fuzzy action mechanism, difficult formula optimization, and poor effect stability; the present application accurately intervenes in the core problem that the seed early development is abnormal due to the insufficient endogenous auxin content in the seed under high-temperature stress, by exogenous application of a low-concentration naphthaleneacetic acid solution to the inflorescence of the main stem of the soybean plant after flowering. The single-component solution not only has a clear and controllable action path, but also realizes targeted protection in the critical window period after flowering, which determines seed development, effectively guarantees the cell cycle process of seed early development under high-temperature stress, lays a physiological foundation for normal development of pods, and significantly improves the pertinence and reliability of regulation.

[0018] The present application investigates the pod development process of the main inflorescence of the soybean plant, the seed ovule and embryo development status and the number of cells thereof, the flower and pod retention rate of the main stem, and the effective pod number, effective grain number, and effective grain weight of the main stem, and determines that the application of a low-concentration naphthaleneacetic acid solution under high-temperature conditions can significantly alleviate the inhibition of high-temperature during flowering on the seed development process, promote the normal development of ovules and embryos, improve the flower and pod retention rate, and increase the number of effective pods and the yield per plant. Furthermore, the application can solve the problem that the application of the soybean flower and pod retention plant growth regulator in the prior art relies on multiple plant hormone complex, and the regulation effect on high-temperature stress is not clear, thereby making it difficult to effectively guarantee soybean seed development under high-temperature stress during flowering. Therefore, the present application not only provides an agronomic control means for effectively alleviating high-temperature stress after flowering of soybean, but also elucidates the action mechanism from the physiological aspect of seed development, thereby providing an implementable technical solution and a corresponding theoretical basis for solving the problem that the application effect of the method for improving high-temperature stress of soybean in the prior art is limited, and the regulation effect on high-temperature stress is not clear.

[0019] 2、The method provided by the application comprises the following steps: after the first flower of the main stem of the soybean plant begins to bloom, applying naphthaleneacetic acid solution to the inflorescence of the first flower node of the main stem of the high-temperature stressed soybean plant, investigating the flower and pod retention rate and yield of the plant during high-temperature stress and after the high temperature is removed, and evaluating the effect of the exogenous naphthaleneacetic acid (auxin analogue) on relieving the high-temperature heat damage of the soybean during the flowering period. In the greenhouse test, after the inflorescence of the first flower node of the main stem of the soybean plant is coated by using the method during the high-temperature stress, the inhibition of the high temperature on the development of the soybean seed and endosperm can be effectively relieved, but the aboveground dry weight of the plant is not affected. After the auxin analogue naphthaleneacetic acid is coated, the effective pod number, effective grain number and effective grain weight of the first flower node of the soybean plant are increased to 2.75 times, 7.95 times and 2.50 times of those under the high-temperature stress, respectively. In the field test, after the inflorescence of the first flower node is sprayed by using the method during the high-temperature stress, the flower retention rate of the plant 6 days, 9 days and 12 days after flowering is 54.6% higher than that of the high-temperature stress treatment on average, the podding rate 30 days after flowering is 40.0% higher than that of the high-temperature stress treatment, and the effective pod number, effective grain number and effective grain weight of the first flower node are increased to 2.05 times, 2.56 times and 1.71 times of those under the high-temperature stress, respectively. The method has good effect on relieving the high-temperature heat damage of the soybean during the flowering period, and is simple and easy to implement. The method provides a method for coping with the yield reduction of the soybean during the flowering period, and has the effects of significantly relieving the inhibition of the high temperature during the flowering period on the development of the seed, improving the flower and pod retention rate, and not affecting the aboveground biomass, and has potential application and research value in coping with the yield reduction of the soybean caused by the high temperature during the flowering period. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The method is used for the influence of the application of naphthaleneacetic acid under the high-temperature stress during the flowering period in the greenhouse scene on the seed development of the first flower node of the soybean; wherein D3, D6 and D9 represent 3 days, 6 days and 9 days after flowering in sequence; The letters a, b and c represent the integument, endosperm and embryo respectively; The scale represents 100 microns; CK, HT and HT+NAA represent the control treatment, high-temperature treatment and 0.1 nM NAA solution (auxin analogue naphthaleneacetic acid solution) applied to the first flower node of the main stem of the soybean plant under the high-temperature stress in sequence.

[0021] Figure 2 The method is used for the influence of the application of naphthaleneacetic acid under the high-temperature stress during the flowering period in the greenhouse scene on the cell structure and number of the seed integument and embryo of the first flower node of the soybean; wherein A is the number of integument cells of the seed of the first flower node of the main stem of the soybean; B is the diameter of the integument cell of the seed of the first flower node of the main stem of the soybean; C is the number of embryo cells of the seed of the first flower node of the main stem of the soybean; D is the size of the embryo of the seed of the first flower node of the main stem of the soybean; CK, HT and HT+NAA represent control treatment, high temperature treatment and high temperature stress under exogenous smearing 0.1nM NAA solution (auxin analog naphthalene acetic acid solution) respectively; Different letters represent significant difference (Duncan method, p <0.05).

[0022] Figure 3 The influence of applying naphthalene acetic acid under high temperature stress during flowering period in greenhouse scenario on the yield of soybean main stem initial flowering node; wherein: A is the flower retention rate of the main stem initial flowering node of soybean 6 days after the first flower of the main stem initial flowering node opens; B is the pod retention rate of the main stem initial flowering node of soybean 30 days after the first flower of the main stem initial flowering node opens; D6 and D30 represent 6 days and 30 days after flowering respectively; CK, HT and HT+NAA represent control treatment, high temperature treatment and high temperature stress under exogenous smearing 0.1nM NAA solution (auxin analog naphthalene acetic acid solution) respectively; Different letters represent significant difference (Duncan method, p <0.05).

[0023] Figure 4 The influence of applying naphthalene acetic acid under high temperature stress during flowering period in greenhouse scenario on the yield of soybean main stem initial flowering node; wherein: A is the effective pod number of the main stem initial flowering node of soybean 60 days after the first flower of the main stem initial flowering node opens; B is the effective grain number of the main stem initial flowering node of soybean 60 days after the first flower of the main stem initial flowering node opens; C is the effective grain weight of the main stem initial flowering node of soybean 60 days after the first flower of the main stem initial flowering node opens; D60 represents 60 days after flowering; CK, HT and HT+NAA represent control treatment, high temperature treatment and high temperature stress under exogenous smearing 0.1nM NAA solution (auxin analog naphthalene acetic acid solution) respectively; Different letters represent significant difference (Duncan method, p <0.05).

[0024] Figure 5 The influence of applying naphthalene acetic acid under high temperature stress during flowering period in greenhouse scenario on the yield of soybean main stem initial flowering node; wherein: A is the plant phenotype of the main stem initial flowering node of soybean 60 days after the first flower of the main stem initial flowering node opens under control treatment; B is the plant phenotype of the main stem initial flowering node of soybean 60 days after the first flower of the main stem initial flowering node opens under high temperature treatment; C is the phenotype of the plant of the main stem of soybean at 60 days after the first flower of the first flower node opens after exogenous application of auxin analog naphthalene acetic acid under high temperature treatment; D is the dry weight of the aboveground part of the plant at 60 days after flowering under different treatments; D60 represents 60 days after flowering; CK, HT and HT+NAA represent the control treatment, high temperature treatment and exogenous application of 0.1nM NAA solution (auxin analog naphthalene acetic acid solution) under high temperature stress, respectively; The scale in the figure is 50cm; The same letter represents no significant difference (Duncan method, p >0.05).

[0025] Figure 6 The influence of application of naphthalene acetic acid under high temperature stress during the flowering period in the field on the flower and pod retention rate of the first flower node of soybean in the present application; wherein: A is the flower retention rate of the first flower node of the main stem of soybean at 6 days, 9 days and 12 days after the first flower of the first flower node opens; B is the pod retention rate of the first flower node of the main stem of soybean at 30 days after the first flower of the first flower node opens; D6, D9 and D12 represent 6 days, 9 days and 12 days after the first flower of the first flower node opens, respectively; CK, HT and HT+NAA represent the control treatment, high temperature treatment and exogenous application of 0.1nM NAA solution (auxin analog naphthalene acetic acid solution) under high temperature stress, respectively; Different letters represent significant differences (Duncan method, p <0.05).

[0026] Figure 7 The influence of application of naphthalene acetic acid under high temperature stress during the flowering period in the field on the yield of the first flower node of soybean in the present application; wherein: A is the number of effective pods of the first flower node of the main stem of soybean; B is the number of effective grains of the first flower node of the main stem of soybean; C is the effective grain weight of the first flower node of the main stem of soybean; CK, HT, HT+NAA and HT+H2O represent the control treatment, high temperature treatment, exogenous application of 0.1nM NAA solution (auxin analog naphthalene acetic acid solution) under high temperature stress, and spraying with the same amount of water as 0.1nM NAA solution under high temperature stress, respectively; Different letters represent significant differences (Duncan method, p <0.05). DETAILED DESCRIPTION

[0027] The present application will be described in detail below with reference to the accompanying drawings and specific embodiments, but should not be understood as limiting the present application. If not specifically stated, the technical means used in the following examples are conventional means familiar to those skilled in the art, and the materials, reagents, etc. used in the following examples, if not specifically stated, can be obtained from commercial channels.

[0028] Example 1: Effect of exogenous application of auxin analogue naphthalene acetic acid to alleviate heat stress during flowering stage of soybean under high temperature scenario in greenhouse A pot experiment was conducted in a greenhouse at the Wuqiao Experimental Station of China Agricultural University (37°29'~37°47'N, 116°19'~116°42'E) in 2024. The details are as follows:

[0029] The soybean variety Qihuang 34 with limited pod setting habit was selected for planting in pots on June 15. The seeds were sown in planting pots (30 cm in diameter and 31 cm in height) filled with 20 L of mixed soil (field soil: nutrient soil, mass ratio = 1:1), and 12 g of controlled-release fertilizer (N:P2O5:K2O nutrient content ratio = 14:14:14) was uniformly mixed into each pot of mixed soil. Uniform and plump seeds were selected for sowing, with a sowing depth of 3 cm and 9 seeds per pot. After the soybean plants grew to two fully expanded compound leaves, thinning was performed, and three uniform seedlings per pot were retained. During the entire growth period of soybean, the plants were adequately irrigated without water stress, and pests, diseases, and weeds were artificially controlled. After the first flower on the main stem of the soybean plant opened, the pots were moved to the greenhouse (4 meters long, 4 meters wide, and 3.5 meters high) for different temperature treatments for 6 days. Normal temperature treatment and high temperature stress treatment were implemented in different greenhouses. The control treatment was a simulated normal temperature outside the greenhouse (control greenhouse, denoted as CK, i.e., control treatment), with a specific temperature setting of 32°C / 22°C (maximum daytime temperature / constant nighttime temperature). Referring to the high temperature threshold during the summer flowering stage of soybean in the local area for many years, the temperature setting for the high temperature treatment in the greenhouse was 40°C / 30°C (high temperature greenhouse, denoted as HT, i.e., high temperature treatment).

[0030] The temperature regulation process in different greenhouses was as follows: the temperature in the control greenhouse and the high temperature greenhouse was set to gradually increase from 6:00 am to 12:00 noon, reaching the maximum at 12:00 noon; then gradually decreased from 12:00 noon to 18:00 in the evening, and the nighttime temperature was maintained constant. In addition to the temperature conditions, the other environmental conditions in the greenhouse were set as follows: the photosynthetic photon flux density (PPFD) averaged 414 µmol m -2 s -1 ; the average relative humidity in the greenhouse was 60%, and the average CO2 concentration was 426 ppm; and the air conditions inside and outside the greenhouse were kept consistent through a natural wind circulation system.

[0031] The method for using the exogenous application of the auxin analog naphthalene acetic acid solution (referred to as naphthalene acetic acid solution, denoted as NAA solution, with a concentration of 0.1 nM) during high temperature treatment is as follows: For soybean plants transplanted into a high temperature greenhouse, the white flower buds at the first flowering node were treated at 19:00 on the day of flowering. A cotton swab was used to dip the freshly prepared 0.1 nM naphthalene acetic acid solution. The target flower was treated by applying the solution to the entire flower, until the petals and sepals were evenly moistened without dripping (the high temperature greenhouse soybean plants treated with the exogenous application of 0.1 nM naphthalene acetic acid solution are denoted as HT+NAA, i.e., the exogenous application of 0.1 nM naphthalene acetic acid solution under high temperature stress; the high temperature greenhouse soybean plants without treatment are denoted as HT, i.e., high temperature treatment). After the high temperature stress ended, the potted plants were removed from the greenhouse and placed in a natural environment for continued growth until physiological maturity. After the different temperature treatments ended, the pods at the first flowering node of the soybean plants were collected 3 days, 6 days, and 9 days after flowering, and the pod and seed development was observed. The size and cell number of the seed coat and embryo were determined. The flower retention rate of the main stem at the first flowering node 6 days after flowering was determined. The pod retention rate of the main stem at the first flowering node 30 days after flowering was determined. The effective pod number, effective grain number, and effective grain weight of the main stem at the first flowering node 60 days after flowering, as well as the aboveground dry weight of the plant, were determined. All data were subjected to ANOVA statistical analysis using SPSS 22, and multiple comparison analysis was performed using the Duncan method, p <0.05, i.e., a significant difference. The results are shown in Figures 1 to 5 .

[0032] Among them, the seeds of the soybean variety Qihuang 34 were purchased from Shandong Shengfeng Seed Industry Technology Co., Ltd.

[0033] The controlled-release fertilizer was purchased from Yihua (Shanghai) Co., Ltd.

[0034] The effect of applying naphthalene acetic acid under high temperature stress during the flowering period in a greenhouse environment on the seed development of the first flowering node of soybean is shown in Figure 1 After using the auxin analog naphthalene acetic acid solution to treat the flower buds of the main stem at the first flowering node of soybean plants, the restriction of high temperature during the flowering period on seed size was effectively alleviated, and the damage caused by high temperature was reduced. Compared with the control, high temperature significantly inhibited seed size, and the exogenous application of the auxin analog naphthalene acetic acid under high temperature stress promoted the development of pods under high temperature.

[0035] The effect of applying naphthalene acetic acid under high temperature stress during the flowering period in a greenhouse environment on the seed coat and embryo cell structure and number of the first flowering node of soybean is shown in Figure 2As shown in the figure, after the flower buds of the first flowering node of the soybean plant were smeared with the auxin analogue naphthalene acetic acid solution, the development of the seed ovule and embryo under high temperature stress during flowering was promoted. Compared with the control, high temperature treatment led to a decrease in the number and size of seed embryo and ovule cells 3 days, 6 days and 9 days after flowering. After the exogenous application of the auxin analogue naphthalene acetic acid solution under high temperature stress, the number and size of ovule cells were significantly greater than those under high temperature stress, and could be restored to the control level; after the application of the auxin analogue naphthalene acetic acid solution, the number and size of soybean seed embryo cells were also significantly higher than those under high temperature stress.

[0036] The effect of applying naphthalene acetic acid under high temperature stress during flowering on the retention of flowers and pods of the first flowering node of soybean plants in a greenhouse environment is shown in the figure Figure 3 As shown in the figure, after the flower buds of the first flowering node of the soybean plant were smeared with the auxin analogue naphthalene acetic acid solution, the development of the seed ovule and embryo under high temperature stress during flowering was promoted. Compared with the control, high temperature treatment led to a decrease in the number and size of seed embryo and ovule cells 3 days, 6 days and 9 days after flowering. After the exogenous application of the auxin analogue naphthalene acetic acid solution under high temperature stress, the number and size of ovule cells were significantly greater than those under high temperature stress, and could be restored to the control level; after the application of the auxin analogue naphthalene acetic acid solution, the number and size of soybean seed embryo cells were also significantly higher than those under high temperature stress.

[0037] The effect of applying naphthalene acetic acid under high temperature stress during flowering on the yield of the first flowering node of soybean plants in a greenhouse environment is shown in the figure Figure 4 As shown in the figure, after the flower buds of the first flowering node of the soybean plant were smeared with the auxin analogue naphthalene acetic acid solution, the development of the seed ovule and embryo under high temperature stress during flowering was promoted. Compared with the control, high temperature treatment led to a decrease in the number and size of seed embryo and ovule cells 3 days, 6 days and 9 days after flowering. After the exogenous application of the auxin analogue naphthalene acetic acid solution under high temperature stress, the number and size of ovule cells were significantly greater than those under high temperature stress, and could be restored to the control level; after the application of the auxin analogue naphthalene acetic acid solution, the number and size of soybean seed embryo cells were also significantly higher than those under high temperature stress.

[0038] The effect of applying naphthalene acetic acid under high temperature stress during flowering on the aboveground dry weight of soybean plants in a greenhouse environment is shown in the figure Figure 5As shown, the use of auxin analog naphthalene acetic acid solution to smear soybean (plant) flower node flower had no significant effect on plant aboveground dry weight. 60 days after flowering, the control treatment, high temperature treatment and application of auxin analog naphthalene acetic acid solution under high temperature stress, the plant aboveground dry weight was 52.91 grams, 42.90 grams and 49.54 grams, respectively, but there was no significant difference between each treatment.

[0039] The above results show that under the scenario of high temperature in the greenhouse, the application of auxin analog naphthalene acetic acid under high temperature stress during the flowering period of soybean can effectively alleviate the adverse effects of high temperature on seed development, improve the flower and pod retention rate under high temperature stress, increase the number of effective pods, effective grains and effective grain weight, indicating that the auxin analog naphthalene acetic acid has the effect of relieving the heat damage of high temperature during the flowering period of soybean.

[0040] Example 2: Effect of exogenous application of auxin analog naphthalene acetic acid to relieve heat damage during the flowering period of soybean under the scenario of high temperature in the field In 2025, field experiments were carried out in Wuqiao Experimental Station of China Agricultural University (north latitude 37°29'~37°47'; east longitude 116°19'~116°42'). The specific is as follows:

[0041] The limited pod setting habit of soybean variety Qihuang 34 was selected, and was sown on June 18. The planting density of summer soybean Qihuang 34 was 312500 plants / hm 2 , row spacing 40 cm, plant spacing 8 cm. After wheat harvest, mechanical ditching was used, and then artificial sowing (3 seeds per hole), sowing depth 3 cm. After the first three leaves of the plant unfolded, the seedlings were fixed. Nitrogen fertilizer (N application amount 90 kg / hm 2 ), phosphorus fertilizer (P2O5application amount 120 kg / hm 2 ) and potassium fertilizer (K2O application amount 100 kg / hm 2) As base fertilizer, it is applied on both sides of the sowing strip, and no topdressing is needed. After the first flower of the main stem opens, different temperature treatments are carried out for 6 days. A plastic arched shed is used to simulate the high temperature environment in the field, and the temperature in the shed is about 5°C higher than the natural temperature in the field. The natural temperature in the field is the control. Before high temperature treatment, the first flower node of the soybean plant is marked, and at 19:00 on the day of flowering, the inflorescence of the first flower node of the main stem of the plant is sprayed with a naphthalene acetic acid solution. The freshly prepared 0.1 nM naphthalene acetic acid solution is loaded into a handheld sprayer, and the inflorescence of the first flower node of the main stem of the soybean plant is sprayed directionally, 2 times of naphthalene acetic acid solution per plant, until the flowers are evenly wetted without dripping. Each mu of land needs to spray about 50 liters of 0.1 nM naphthalene acetic acid solution. Field cultivation and water and fertilizer management measures are carried out according to the conventional method. After the high temperature stress is over, the high temperature shed is removed, and the natural growth conditions in the field are restored, and the plant grows to physiological maturity. After different temperature treatments are over, the flower retention rate of the first flower node of the main stem 6 days, 9 days and 12 days after flowering is measured; the pod retention rate of the first flower node of the main stem 30 days after flowering is measured; the effective pod number, effective grain number and effective grain weight of the first flower node of the main stem after the plant grows to physiological maturity are measured. All data are analyzed by SPSS 22 for ANOVA statistical analysis, and Duncan method is used for multiple comparison analysis, p <0.05 is considered to be a significant difference. The results are shown in Figures 6 to 7 .

[0042] The effect of naphthalene acetic acid application on the flower and pod retention rate of the first flower node of soybean under high temperature stress in the field during the flowering period is shown in Figure 6As shown, spraying soybean plants with a naphthalene acetic acid solution after the first flower node of the inflorescence can significantly alleviate the flower and pod drop caused by high temperature. Six days after flowering, the flower retention rates of the first flower node of the main stem of soybean plants under the control treatment, high temperature treatment, and high temperature stress with the application of a naphthalene acetic acid solution were 92.61%, 58.23%, and 91.43%, respectively. Under high temperature stress, the flower retention rate after the application of a naphthalene acetic acid solution was 33.20% higher than that without the application. Nine days after flowering, the flower retention rates of the first flower node of the main stem of soybean plants under the control treatment, high temperature treatment, and high temperature stress with the application of a naphthalene acetic acid solution were 84.80%, 54.26%, and 85.18%, respectively. Under high temperature stress, the flower retention rate after the application of a naphthalene acetic acid solution was 30.92% higher than that without the application. Twelve days after flowering, the flower retention rates of the first flower node of the main stem of soybean plants under the control treatment, high temperature treatment, and high temperature stress with the application of a naphthalene acetic acid solution were 72.42%, 46.44%, and 69.59%, respectively. Under high temperature stress, the flower retention rate after the application of a naphthalene acetic acid solution was 23.15% higher than that without the application. Thirty days after flowering, the pod retention rates of the first flower node of the main stem of soybean plants under the control treatment, high temperature treatment, and high temperature stress with the application of a naphthalene acetic acid solution were 60.83%, 45.88%, and 64.20%, respectively. Under high temperature stress, the pod retention rate after the application of a naphthalene acetic acid solution was 18.32% higher than that without the application.

[0043] The effect of the application of naphthalene acetic acid under high temperature stress during the flowering period in the field on the yield of the first flower node of soybean is shown in Figure 7 As shown, spraying the first flower node of the inflorescence with a naphthalene acetic acid solution can significantly alleviate the yield reduction caused by high temperature. After the soybean plants were physiologically mature, the plants under different treatments were harvested to examine the effective pod number, effective grain number, and effective grain dry weight of the first flower node. The results showed that the average effective pod number of the first flower node of the main stem of soybean plants under the control treatment, high temperature treatment, high temperature stress with the application of a naphthalene acetic acid solution, and high temperature stress with the application of an equal amount of water instead of the naphthalene acetic acid solution was 6.25, 2.86, 5.86, and 3.00, respectively; the effective grain number was 15.75, 6.25, 16.00, and 6.25, respectively; and the effective grain dry weight was 3.75 g, 2.03 g, 3.47 g, and 0.15 g, respectively. After the application of a naphthalene acetic acid solution, the effective pod number, effective grain number, and effective grain dry weight of the first flower node increased by 2.05 times, 2.56 times, and 1.71 times, respectively, compared to those under high temperature stress.

[0044] The above results show that under the high temperature scenario in the field, the application of auxin analogue naphthalene acetic acid solution during the flowering period of soybean can significantly improve the flower and pod retention rate of the main stem of soybean under high temperature stress, increase the number of effective pods, the number of effective grains and the weight of effective grains, indicating that the auxin analogue naphthalene acetic acid has the effect of relieving high temperature heat damage during the flowering period of soybean.

[0045] Comparative Example 1 A method for improving the heat tolerance of plants (Chinese patent with publication number CN113575180A): Comparative Example 1 uses the model plant Arabidopsis thaliana as the material, and sprays naphthalene acetic acid on the plant before flowering, and then performs high temperature stress treatment. By observing the development of the female gametophyte under high temperature conditions, and taking the number of normal female gametophytes and the final seed setting rate as the core indicators, the regulatory effect of the auxin analogue naphthalene acetic acid on high temperature tolerance is evaluated.

[0046] Compared with Comparative Example 1, the method proposed by the present application further expands the application scope, and is no longer limited to the model plant Arabidopsis thaliana, but focuses on the actual problems in soybean production in the face of national food security needs. The method proposed by the present application aims at the adverse effects of high temperature during the flowering period on the yield formation of soybean, and systematically optimizes the problem of high temperature stress during the reproductive period of soybean, thereby improving the applicability and popularization value of the method in actual agricultural production. The specific differences between the two are as follows: first, precise application: the application time of the auxin analogue naphthalene acetic acid solution is adjusted to the occurrence of high temperature stress, and is applied directly to the inflorescence of the soybean plant, making its effect more direct and targeted; second, concentration optimization: a lower and more economical effective concentration is used; third, multi-scenario verification: through the combination of greenhouse controllable tests and field production tests, the effect of effectively relieving high temperature heat damage during the flowering period is fully verified. The method promotes the normal development of soybean seeds under high temperature stress, reduces the flower and pod drop rate, and ultimately realizes the stability and improvement of yield. Its core value lies in fundamentally solving the problem of stable yield of crops under high temperature stress, and has important application and popularization value.

[0047] Comparative Example 2 A method for restoring male sterility of a plant in the family Poaceae and a male sterility restorer (Chinese patent with publication number CN102348385A): The method of the present application is used to restore the male sterility of soybean under high temperature stress. The method is applied to the soybean seed development stage, i.e. the grain formation stage. The method is to apply an auxin analogue, such as indole-3-acetic acid (IAA), α-naphthaleneacetic acid (NAA) or 2,4-dichlorophenoxyacetic acid (2,4-D), etc. to the stems and leaves of the plants by spraying, to promote pollen development by exogenous supply of auxin, thereby restoring fertility under high temperature stress.

[0048] Compared with Comparative Example 2, the core objective of the method of the present application is to promote soybean seed grain formation and increase the rate of flower and pod retention, to ensure high yield and stable yield of soybean under high temperature stress during the flowering period. The technical solution of the method of the present application and the technical solution of Comparative Example 2, which aims to restore the pollen fertility of cereal crops, are fundamentally different in technical objective. The above difference is due to the difference in the key physiological stages of the two methods: the method of the present application acts on the early stage of soybean seed development, i.e. the grain formation stage, while the method of Comparative Example 2 acts on the pollen development stage. Therefore, the physiological process regulated by the auxin analogue naphthaleneacetic acid in the method of the present application and its mechanism of action are essentially different from those of Comparative Example 2. In addition, the reliability of the technical solution of the present application has not only passed the strict verification of the controllable environment in the greenhouse, but also shown consistent and stable yield-increasing effect in field production test, proving its practical application value and reliability.

[0049] From the above, the outstanding advantages of the present application are: the technical orientation is clear, based on the demand of national food security, aiming at the solution of the problem of yield potential restriction caused by high temperature during flowering period in soybean production; the technical scheme is innovative, by accurately applying low-concentration auxin analogue naphthalene acetic acid at the key period after the beginning of flowering of soybean, the effective grain formation is ensured, the early development process of seeds is regulated, and the yield per unit of soybean is improved; the technical effect is fully verified, the method proposed in the present application is verified under controllable conditions in greenhouse and field production conditions, and stable yield-increasing effect is shown, indicating that the method has good reliability and generalizability in complex production environment; the application cost advantage is obvious, the effective application concentration used is lower than that of the prior art, which reduces the application cost while ensuring the technical effect. In summary, the present application proposes a production method that is optimized and verified in multiple environments, which is different from the existing comparative technology in terms of application target, action stage, action mechanism and verification level, and has clear technical progress and practical application value.

[0050] At the same time, by investigating the pod development process of the main inflorescence of the first flowering node of soybean plant, the seed ovule and embryo development status and the number of cells thereof, the flower and pod retention rate of the first flowering node, and the effective pod number, effective grain number and effective grain weight of the first flowering node, it is clear that under high temperature conditions, the application of low-concentration auxin analogue naphthalene acetic acid solution can significantly alleviate the inhibition of high temperature on the seed development process, promote the normal development of ovule and embryo, increase the flower and pod retention rate, and increase the number of effective pods and yield per plant. Based on the above results, the method proposed in the present application can solve the problem that in the prior art, the application of soybean flower and pod retention plant growth regulator depends on the compounding of multiple plant hormones, and the regulation effect on high temperature stress is not clear, so it is difficult to effectively ensure the development of soybean seeds under high temperature stress. Therefore, the present application not only provides an agronomic regulation means for effectively alleviating high temperature stress after the beginning of flowering of soybean, but also elucidates the action mechanism from the physiological aspect of seed development, thereby providing an implementable technical scheme and corresponding theoretical basis for solving the problem of lack of regulation method for high temperature stress during flowering period of soybean and unclear action mechanism in the prior art.

[0051] It should be noted that when numerical ranges are involved in the present application, both endpoints of each numerical range and any number between the two endpoints can be selected, and in order to prevent repetition, the preferred embodiments are described in the present application.

[0052] Although the preferred embodiments of the present application have been described, those skilled in the art can make further changes and modifications to these embodiments once they know the basic inventive concept, and all changes and modifications falling within the scope of the present application.

Claims

1. A method for improving the heat resistance of soybeans during flowering, characterized in that, Includes the following steps: After the first flower of the main stem of soybean opens, naphthaleneacetic acid solution is applied exogenously to the inflorescence of the main stem of soybean under high temperature stress to alleviate the high temperature heat damage during the flowering period of soybean plants. The application rate of the naphthaleneacetic acid solution is 45L / mu to 55L / mu.

2. The method according to claim 1, characterized in that, The concentration of the naphthaleneacetic acid solution is 0.08 nM to 0.12 nM.

3. The method according to claim 2, characterized in that, The naphthaleneacetic acid solution is applied by spraying or smearing.

4. The method according to claim 3, characterized in that, The naphthaleneacetic acid solution was applied on the day the first flower of the soybean main stem opened.

5. The method according to claim 4, characterized in that, Improving the heat tolerance of soybeans during flowering includes increasing the number of effective pods, effective grains, and effective grain weight at the first flowering node of the soybean main stem under high temperature stress.

6. The method according to claim 4, characterized in that, Improving the heat tolerance of soybeans during flowering includes promoting the development of pods at the first flowering node of the soybean main stem under high temperature stress.

7. The method according to claim 4, characterized in that, Improving heat tolerance during soybean flowering includes increasing the size and number of cells in the integument and embryo of the seed in the first flowering node of the soybean main stem under high temperature stress.

8. The method according to claim 1, characterized in that, The soybean variety mentioned includes Qihuang 34.

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