Method for evaluating salt tolerance of rice based on reflectance spectroscopy

Abstract

The present invention belongs to the field of rice salt-tolerance research, and specifically relates to a method for accurately evaluating salt tolerance of rice using spectroscopy. Compared with conventional salt-tolerance evaluation methods, the present technical solution can significantly shorten the testing cycle, increase evaluation efficiency, and reduce test errors caused by human factors. In addition, the evaluation method of the present invention uses the variation of spectral indices to evaluate the salt tolerance of rice seedlings, greatly improving resolution, enabling more accurate evaluation of salt-tolerance capability, and also greatly improving the repeatability and stability of evaluation results for salt tolerance at the rice seedling stage.

Description

A rice salt tolerance evaluation method based on reflectance spectrum TECHNICAL FIELD

[0001] The present application belongs to the field of rice salt tolerance research, and particularly relates to a rice salt tolerance evaluation method based on reflectance spectrum. BACKGROUND

[0002] Due to the increasingly serious problem of farmland salinization, most of the saline-alkali lands have abundant rainwater resources, and have great comprehensive utilization potential, and breeding salt-tolerant varieties is one of the most effective ways to utilize saline-alkali lands. Therefore, it is of great significance to clarify the physiological mechanism of rice salt tolerance, to mine the genes regulating rice salt tolerance, and to develop the corresponding molecular markers for rice salt tolerance genetic breeding.

[0003] The research on rice salt tolerance physiology and related genetic mechanisms is based on a stable salt tolerance phenotype evaluation system. According to different growth and development processes of rice, the growth period of rice can be divided into five stages, namely seed germination stage, seedling stage, heading stage, flowering stage and maturation stage, and the seedling stage of rice is most sensitive to salt stress, so identifying the salt tolerance of rice seedling is of great significance for breeding salt-tolerant rice varieties. TECHNICAL PROBLEM

[0004] The existing rice seedling salt tolerance evaluation refers to the salt tolerance evaluation standard of International Rice Research Institute, which divides the salt tolerance of rice into five levels, 1, 3, 5, 7 and 9, corresponding to extremely strong, strong, medium, weak and extremely weak salt tolerance, respectively. This method has the problems of low evaluation precision, great influence of subjective factors on salt tolerance level evaluation, and poor repeatability, so it is difficult to obtain reliable results in salt tolerance gene mining and related research. Therefore, it is of great significance to develop a rice seedling salt tolerance identification method with high throughput and good stability for the research of rice salt tolerance and the breeding of salt-tolerant rice varieties. TECHNICAL SCHEME

[0005] The present application provides a rice salt tolerance evaluation method based on reflectance spectrum, which can significantly shorten the test period, improve the salt tolerance evaluation efficiency, reduce the test errors caused by human factors, and greatly improve the repeatability and stability of the evaluation results of rice seedling salt tolerance.

[0006] The technical scheme of the present application is realized as follows:

[0007] A rice salt tolerance evaluation method based on reflectance spectrum, comprising the following steps:

[0008] (1) Cultivation of seedlings

[0009] The rice seedlings are fixed in the seeding groove and moved into the hydroponic box for culture; a partition is arranged between the adjacent seeding grooves, and a culture solution is added into the hydroponic box; a culture solution circulating device is started to make the culture solution circulate and flow;

[0010] (2) Salt stress treatment

[0011] The cultured seedlings are placed into the culture solution containing NaCl for salt stress treatment, one day before the salt treatment, the plants with relatively uniform growth are selected in each hydroponic box, a horizontal bar is drawn on the position of the 1.5 leaf tips of the rice plants as a mark; the spectrum of the marked leaves is measured one day before the salt treatment and on the 1st, 3rd and 5th day after the salt treatment, the spectrum index of different days after the treatment is divided by the spectrum index one day before the treatment, to obtain the change amount of the spectrum index of the leaves of different days after the treatment, the greater the change amount of the spectrum index, the better the salt tolerance of the seedlings; the calculation formula of the spectrum index CRI1 is as follows:

[0012] CRI1 = 1 / R 510 - 1 / R 550

[0013] In the formula, R 510 represents the spectral reflectance at λ = 510 nm; R 550 represents the spectral reflectance at λ = 550 nm.

[0014] Further, in the step (1), the seeds of the rice after germination are sowed in the seeding groove, after the seeds are sowed, the seeds are covered with a paper towel, then water is sprayed to make the seeds and the paper towel adhere to the seeding groove, and then the seeding groove is placed in the hydroponic box until the water is 1 cm above the seeds.

[0015] Further, the rice seed germination method is as follows: the full and uniform rice seeds with perfect glumes are selected, the seeds are soaked for 48 hours, the water is replaced every 12 hours during the soaking, and the seeds are germinated for 12 hours after the soaking.

[0016] Further, the seeds after germination are cultured in pure water for 3 days and then moved into the Yoshida nutrient solution.

[0017] Further, in the step (1), the length of the partition is not less than the length of the plant root system; the same variety of rice seeds is sowed in each seeding groove.

[0018] Further, in the step (1), the culture solution circulating device is a water pump with a flow rate of 600 L / h; the culture solution is replaced every 6 days.

[0019] Further, in the step (1), the group culture lamp is arranged above the hydroponic box for light supplement, so that the difference between the light intensities of different cultivation positions in the whole hydroponic box is not more than 5%.

[0020] Further, the light supplementing method is as follows: taking the culture shelf with the water culture box placed thereon as an example, the culture shelf has a length of 1 m and a width of 0.5 m, two tissue culture lamps with the same interval are installed on the top of the culture shelf, one lamp is installed at a position 15 cm below the top lamps before and after the culture, two lamps are vertically installed at positions 10 cm and 40 cm in the width direction of the left and right sides, respectively, and the front, rear, left and right different areas are supplemented with light, respectively; meanwhile, silver reflective cloth is installed at the front and rear positions of the culture shelf to completely shield the front and rear reflections.

[0021] Further, the step (2) is that the spectrum of the marked leaf is measured one day before the salt treatment and five days after the salt treatment.

[0022] Further, the calculation formula of the mortality rate and the change amount of the spectrum index is as follows:

[0023] Mortality rate = -109.714x + 100.628, x is the change amount of the spectrum index one day before the salt treatment and five days after the salt treatment.

[0024] Further, the step (2) is that the spectrum is measured by using a handheld plant reflectance spectrum measuring instrument of Czech PSI Polypen RP-410.

[0025] Further, the step (2) is that the spectrum measurement position is the middle position of the length of the marked leaf, and the time for measuring the spectrum of the leaf each time is 15:00-18:00.

[0026] Further, the step (2) is that the rice seedlings are treated with Yoshida nutrient solution with a salt concentration of 0.8 % after growing to the two-leaf-one-heart stage.

[0027] The above-mentioned method is applied to evaluate the salt tolerance of rice germplasm and / or predict the mortality rate in the salt tolerance experiment. Beneficial effects

[0028] The present application adopts a spectrometer to measure the spectral data of the leaves, and then performs salt tolerance evaluation according to the change amount of the calculated spectral index, compared with the traditional salt tolerance evaluation method, the technical scheme can significantly shorten the test cycle, improve the salt tolerance evaluation efficiency, and reduce the test error caused by human factors. The present application compares the salt tolerance by using the change amount of the spectral index, greatly improves the resolution, and is more accurate in evaluating the salt tolerance, and greatly improves the repeatability and stability of the evaluation result of the salt tolerance of rice seedlings. In the experiment process, different rice varieties can be sown in different sowing grooves by using the evaluation method, the setting of the partition plate can avoid the root contact of the plants in different sowing grooves, and then the plants are uniformly placed in the water culture box for culture, the culture conditions such as culture solution, temperature and light are kept uniform, the salt tolerance of multiple rice varieties can be evaluated at one time, the salt tolerance difference between different varieties is compared, and the salt tolerance evaluation efficiency is greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0030] Fig. 1 is the growth effect of 19X rice seedlings in the sowing groove.

[0031] Fig. 2 is the difference of root area and leaf area of a single variety under different treatments.

[0032] Fig. 3 is the difference of root area and leaf area of different varieties under different treatments.

[0033] Fig. 4 is a comparison picture of light intensity before and after light supplement, A is before light supplement, and B is after light supplement.

[0034] Fig. 5 is the repeatability difference of dead seedling rate under different light uniformity conditions, A is before light supplement, and B is after light supplement.

[0035] Fig. 6 is a comparison of the correlation between the change amount of spectral index (CRI1) and the dead seedling rate after different days (1, 3, 5 days) of salt treatment, A is the correlation between the salt tolerance rating and the dead seedling rate, B is the correlation between the change amount of spectral index and the dead seedling rate after 1 day of salt treatment, C is the correlation between the change amount of spectral index and the dead seedling rate after 3 days of salt treatment, and D is the correlation between the change amount of spectral index and the dead seedling rate after 5 days of salt treatment.

[0036] Fig. 7 is a repeatability comparison between the traditional method and the improved method, A is the traditional method, and B is the improved method.

[0037] Figure 8 is a histogram of the salt tolerance rating frequency distribution of the conventional method.

[0038] Figure 9 is a histogram of the amount of change in the spectral index (CRI1) for each variety in the improved method. Embodiments of the present application

[0039] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application. Embodiments

[0040] A rice salt tolerance evaluation method based on reflectance spectroscopy comprises the following steps:

[0041] (1) Cultivation of seedlings

[0042] A partition plate is arranged outside the edge of the seeding groove as shown in Figure 1. The seeds after germination are sown in the seeding groove. After sowing the seeds, the seeds are covered with a paper towel. Then water is sprayed to make the seeds and the paper towel adhere to the seeding groove. Then the seeding groove is placed in the water culture box until the water is 1 cm above the seeds. The germinated seeds are cultured in pure water for 3 days and then cultured in Yoshida nutrient solution (pH = 5.9~6.1) until the two-leaf-one-heart stage. After adding the culture solution in the water culture box, the culture solution circulation device is started to make the culture solution circulate and flow. The culture solution circulation device is a water pump with a flow rate of 600 L / h. The culture solution is replaced every 6 days until the end of the experiment.

[0043] In step (1), the method for germinating the rice seeds is as follows: select full and uniform rice seeds with perfect glumes, soak the seeds for 48 hours, replace the water every 12 hours during the soaking, and then germinate the seeds for 12 hours after soaking.

[0044] The length of the partition plate is not less than the length of the plant root system.

[0045] A group culture lamp is arranged above the water culture box for light supplement, so that the difference between the light intensities of different cultivation positions in the whole water culture box is not more than 5%.

[0046] The specific method of light supplement operation is as follows: taking the open type culture shelf with a size of 1 m in length and 0.5 m in width as an example, two group culture lamps with the same interval are installed at the top of the culture shelf. One lamp is installed at the position 15 cm below the lamp tube at the top of the front and rear of the culture shelf, respectively. Two lamps are vertically installed at the positions of 10 cm and 40 cm in the width direction on the left and right sides, respectively, to supplement light for different areas in front, rear, left and right. At the same time, silver reflective cloth is installed at the front and rear positions of the culture shelf to completely block the reflection.

[0047] (2) Salt stress treatment

[0048] After the rice seedlings grow to the two-leaf-one-heart stage, they are treated with Yoshida nutrient solution with a NaCl mass concentration of 0.8% for 6 days. One day before the salt stress treatment, plants with relatively uniform growth are selected, and a horizontal bar is drawn at the position of the tip of the 1.5-leaf leaf of the rice plant using a marking pen as a marker. The marked leaves one day before the salt treatment and on the 1st, 3rd and 5th days after the salt treatment (with the salt treatment taken as the 1st day) are measured for spectra using a Czech PSI Polypen RP-410 handheld plant reflectance spectrometer. The measurement position is the middle position of the length of the marked leaf, and the time for measuring the leaf spectrum each time is 15:00-18:00. The spectral index of each day after the treatment is divided by the spectral index one day before the treatment to obtain the change amount of the leaf spectral index on different days after the salt treatment. The greater the change amount of the spectral index, the better the salt tolerance of the seedling. The calculation formula of the spectral index CRI1 is as follows:

[0049] CRI1= 1 / R 510 – 1 / R 550

[0050] In the formula, R 510 represents the spectral reflectance at λ = 510 nm; and R 550 represents the spectral reflectance at λ = 550 nm.

[0051] (3) Recovery culture

[0052] After the photographing, the plants are reassembled in the original order, and then cultured with nutrient solution without NaCl for 7 days. The number of dead single plants (plants without green leaves are counted as dead single plants) is counted, and the dead seedling rate is calculated. The dead seedling rate = number of dead plants / total number of plants x 100%.

[0053] Among them, the spectral index change amount on the 5th day has the best correlation with the dead seedling rate, the accuracy of predicting the dead seedling rate is the highest, and the salt tolerance rating is more accurate. The calculation formula of the dead seedling rate and the change amount of the spectral index is: dead seedling rate = -109.714x + 100.628, x is the change amount of the spectral index one day before the salt treatment and on the 5th day after the salt treatment.

[0054] Two rice varieties, 19X and SLY138, are selected, and single variety cultivation and mixed cultivation of two varieties are used. Four treatments are set for each cultivation method. The specific conditions of each treatment are as follows.

[0055] Single variety cultivation

[0056] (1) Cross

[0057] The same variety is sowed in the adjacent seeding groove, and no partition is arranged, and the culture solution does not flow in a cycle.

[0058] (2) Cross circulation

[0059] The same variety is sowed in the adjacent seeding groove, and no partition is arranged, and the culture solution flows in a cycle.

[0060] (3) Isolation without circulation

[0061] The same variety is sowed in the adjacent seeding groove, and a partition is arranged, and the culture solution does not flow in a cycle.

[0062] (4) Isolation with circulation

[0063] The same variety is sowed in the adjacent seeding groove, and a partition is arranged, and the culture solution flows in a cycle.

[0064] 2. Two varieties are mixedly cultivated

[0065] (1) Cross between varieties

[0066] The two different varieties 19X and SLY138 are sowed in the adjacent seeding groove, and no partition is arranged, and the culture solution does not flow in a cycle.

[0067] (2) Cross circulation between varieties

[0068] The two different varieties 19X and SLY138 are sowed in the adjacent seeding groove, and no partition is arranged, and the culture solution flows in a cycle.

[0069] (3) Isolation without circulation between varieties

[0070] The two different varieties 19X and SLY138 are sowed in the adjacent seeding groove, and a partition is arranged, and the culture solution does not flow in a cycle.

[0071] (4) Isolation with circulation between varieties

[0072] The two different varieties 19X and SLY138 are sowed in the adjacent seeding groove, and a partition is arranged, and the culture solution flows in a cycle.

[0073] Each treatment has 2 repetitions.

[0074] The white seeds are selected and sowed in the seeding groove according to the above treatment, the seeding groove is placed in the water culture box, and water is added in the water culture box until the water surface is 1 cm above the seeds. After 3 days of seedling, the culture solution is replaced, and after 7 days of culture, the photos are taken. The root area and leaf area are measured by Photoshop software. The results are shown in Tables 1-2 and Figs. 4-5.

[0075] Table 1 Comparison of leaf area and root area of different treatments of a single variety (cm 2 )

[0076]

[0077] Table 2 Comparison of leaf area and root area of two varieties under different treatments (cm 2 )

[0078]

[0079] As shown in Tables 1-2 and Figures 2-3, in the case of no circulating flow of the nutrient solution, the root area and leaf area of the single variety isolation were higher than those of the single variety crossing. The root area and leaf area of the variety crossing were lower than those of the single variety crossing, indicating that the root exudates of different varieties affect the growth state. The root area and leaf area of the 19 fragrant variety under the variety isolation circulation treatment were significantly higher than those under other treatment groups. The root area of the Shuangliangyou 138 variety under the variety isolation circulation and the crossing circulation was significantly different, but the leaf area was not significantly different. The test results show that among all the treatments, the single variety isolation circulation and the variety isolation circulation significantly improve the root area and leaf area of the plant growth, so that the plant achieves a better healthy state, and the test results are more accurate.

[0080] The 96-well PCR plate was cut into 8 strips of 12 wells (8 x 12 wells) in the length direction, and each strip was used as a seeding groove. The extraction rod clamp was assembled for standby. Referring to the method of Example 1, 83 materials with better representation were screened, and the variety numbers of the materials are shown in Table 3. The 83 materials were derived from the International Rice Research Institute, and all rice germplasm resources were derived from the 3K rice sequencing population, and the numbers and names were the same as the 3K sequencing population. The bottom of the seeding groove assembled by the extraction rod clamp (with a transparent plastic sheet as a partition) was seeded, and two treatments were set, namely uneven light (without light compensation) and uniform light (after light compensation treatment), with two replicates.

[0081] After 3 days of pure water culture, the Yoshida nutrient solution (pH = 5.9~6.1) was changed for 7 days, then the nutrient solution with a salinity of 0.8% was changed for 6 days, and finally the salt-free nutrient solution was changed for 7 days to count the dead seedling rate (no green leaf survival was counted as a dead single plant, and the dead seedling rate = dead plant number / total plant number x 100%). Except for the pure water culture stage, the nutrient solution was circulated in the remaining stages, and the circulation power was provided by the water pump mentioned above.

[0082] The light intensity before and after light compensation is shown in Figure 4, where the maximum light intensity is 308001ux, and each value in Figure 4 is the maximum light intensity ratio of the measurement position. The calculation method is as follows:

[0083] Maximum light intensity ratio (%) = measured position light intensity / maximum light intensity x 100%

[0084] As shown in Figure 4, compared with the modified light, the light distribution uniformity after modification is better, and the difference between the light intensities at different cultivation positions in the water culture box is not more than 5%.

[0085] The dead seedling rate before and after light supplement is compared as shown in Figure 5.

[0086] 2 times of repeated experiments are compared, the repeatability of the dead seedling rate of 2 times of experiments before light supplement is poor, and the r value is only 0.4901 (A in Figure 5), while in the environment with uniform light distribution after light supplement, the repeatability of the dead seedling rate of 2 times of experiments is greatly improved, and the r value reaches 0.8075 (B in Figure 5). The test results show that, compared with before light supplement, the light distribution of each position of the culture shelf is uniform after light supplement, the repeatability of the dead seedling rate between repeated experiments is high, and the repeatability and stability of the test results are significantly improved.

[0087] A 12-hole seeding groove is used, and the method of reference example 1 is used to compare the influence of different culture methods and evaluation methods on the salt tolerance grade evaluation of rice.

[0088] (1) Traditional culture method and evaluation method

[0089] 83 materials (variety numbers are shown in Table 3) with better representation are screened, the 83 materials are from the International Rice Research Institute, and all the rice germplasm resources are from the 3K rice sequencing population, and the numbers and names are the same as the 3K sequencing population. All the materials are seeded in 96-hole seeding grooves (not cut), the seeding grooves are placed in the water culture box, and water is added in the water culture box until the water surface is 1 cm above the seeds, and then the Yoshida nutrient solution is changed after 3 days of seedling to the two-leaf-one-heart stage, and then treated with 0.8% sodium chloride (mass fraction) for 6 days, 9 seedlings are taken from each seeding groove, and then different varieties are rated according to the average dead leaf percentage grading standard formulated by the International Rice Research Institute. The evaluation method is as follows: the dead leaf number (the completely withered leaf is counted as a dead leaf) and the total leaf number of each test material are counted, the dead leaf rate is calculated, and the dead leaf rate = dead leaf number / total leaf number x 100%. Finally, the dead seedling rate is counted after 7 days of recovery culture with salt-free nutrient solution.

[0090] Salt tolerance grade evaluation method:

[0091] 1st grade: 0≤dead leaf rate≤20%

[0092] 3rd grade: 20%<dead leaf rate≤40%

[0093] 5th grade: 40%<dead leaf rate≤60%

[0094] 7th grade: 60%<dead leaf rate≤80%

[0095] 9th grade: 80%<dead leaf rate≤100%

[0096] Improved method (the method described in the application)

[0097] The germinated rice seeds are sowed in the sowing tank (transparent plastic sheet is adhered as a partition) which is cut and assembled. Different rice varieties are sowed in different sowing tanks respectively. The presence of the partition can avoid the root contact between different rice varieties, and the nutrient solution circulates and flows, the temperature and light conditions are kept uniform, which can ensure the uniformity of the cultivation conditions of different rice varieties. The spectral data are measured 1 day before the salt stress treatment and 1, 3 and 5 days after the treatment.

[0098] After 6 days of salt stress culture, the dead seedlings are counted after 7 days of recovery culture in the nutrient solution without salt. The dead seedling rate is counted by the method described above.

[0099] The results are shown in FIG. 6, FIG. 7 and FIG. 8. The average value of the spectral index change amount of each sample is shown in FIG. 9.

[0100] As shown in FIG. 6, the correlation between the salt tolerance rating of the traditional evaluation method and the dead seedling rate is poor, and the R 2 value is only 0.5049 (A in FIG. 6). The correlation between the spectral index change amount in the improved method and the dead seedling rate is higher and higher as the salt treatment time is prolonged, and the correlation between the CRI1 change amount (after 5 / 1) on the 5th day of salt treatment and the dead seedling rate is the highest, and the R 2 value is 0.7959 (D in FIG. 6), which highlights the accuracy of the method in predicting the dead seedling rate. Therefore, the CRI1 change amount CRI1 (after 5 / 1) on the 5th day of salt treatment can be used to evaluate the salt tolerance of the seedlings, and the greater the value of the CRI1 change amount (after 5 / 1), the stronger the salt tolerance.

[0101] As shown in FIG. 7, the repeatability of the salt tolerance rating of the traditional evaluation method is poor, and the r value is 0.5779 (A in FIG. 7), while the repeatability of the CRI1 change amount (the last 5 / the first 1) in the improved method is better, and the r value is 0.7892 (B in FIG. 7), which greatly improves the repeatability of the test results. As shown in FIG. 8, the traditional evaluation method only divides the salt tolerance of rice seedlings into five levels, 1, 3, 5, 7 and 9, corresponding to the average dead leaf percentage of dead leaf rate ≤ 20%, 20% < dead leaf rate ≤ 40%, 40% < dead leaf rate ≤ 60%, 60% < dead leaf rate ≤ 80% and 80% < dead leaf rate ≤ 100%, and the resolution is low. The improved method can further subdivide on this basis, and can measure the spectral index change amount of the leaf before and after salt treatment. The CRI1 change amount (the last 5 / the first 1) of each variety is different, which greatly improves the resolution (FIG. 9). By comparing the size of the CRI1 change amount (the last 5 / the first 1) (denoted as CRI1' in Table 3), the salt tolerance is evaluated, and the evaluation result is more accurate. For example, the two materials with serial numbers 7 and 17, the salt tolerance rating of the traditional method is 9, and the dead seedling rate of two times of repetition is also very close, and the difference in salt tolerance of the two materials is difficult to accurately judge. Using the method described in the application, the CRI1 change amount (the last 5 / the first 1) values of two repeated tests are 0.24699 and 0.11729 and 0.48902 and 0.34930 respectively. It can be seen that the salt tolerance of the material No. 7 is greater than that of the material No. 17, and the results of comparing the dead seedling rate and the CRI1 change amount (the last 5 / the first 1) value of the two materials are the same.

[0102] Table 3 Comparison of salt tolerance evaluation results of 83 rice materials by different methods.

[0103]

[0104]

[0105]

[0106] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for evaluating precise salt tolerance of rice by using spectrum, characterized in that, The method comprises the following steps: (1) Cultivation of seedlings Rice seedlings are fixed in the seeding groove and moved into the hydroponic box for cultivation; a partition is arranged between adjacent seeding grooves, and a culture solution is added into the hydroponic box; a culture solution circulating device is started to make the culture solution circulate and flow; (2) Salt stress treatment and photographing The cultivated seedlings are placed in a culture solution containing NaCl for salt stress treatment; one day before the salt treatment, plants with relatively uniform growth are selected in each hydroponic box, and a horizontal bar is drawn on the marked leaf tip of the rice plant at a position of 1.5 leaves with a marking pen as a mark; the spectrum of the marked leaf is measured one day before the salt treatment and one, three and five days after the salt treatment; the spectrum index of different days after the salt treatment is divided by the spectrum index one day before the treatment to obtain the change amount of the spectrum index of the leaf of different days after the salt treatment; the greater the value of the change amount of the spectrum index, the better the salt tolerance of the seedlings; the calculation formula of the spectrum index CRI1 is as follows: CRI1 = 1 / R 510 - 1 / R 550 wherein R 510 represents the spectral reflectance at λ = 510 nm; R 550 represents the spectral reflectance at λ = 550 nm.

2. The method for evaluating the precise salt tolerance of rice by using spectrum according to claim 1, wherein, In the step (1), the seeds of the rice after germination are sown in the seeding groove, the seeds are covered with a paper towel, then water is sprayed to make the seeds and the paper towel adhere to the seeding groove, and then the seeding groove is placed in the hydroponic box until the water is 1 cm above the seeds; the rice seed germination method is as follows: select full and uniform rice seeds with perfect husks, soak the seeds for 48 hours, replace the water every 12 hours during the soaking, germinate the seeds for 12 hours after soaking, and then cultivate the germinated seeds in pure water for 3 days and move them to Yoshida nutrient solution; the length of the partition is not less than the length of the plant root system; the same variety of rice seeds is sown in each seeding groove.

3. The method for evaluating the precise salt tolerance of rice by using spectrum according to claim 1, characterized in that, In the step (1), the culture solution circulating device is a water pump with a flow rate of 600 L / h; the culture solution is replaced every 6 days.

4. The method for evaluating the precise salt tolerance of rice by using spectrum according to claim 1, characterized in that, In the step (1), a tissue culture lamp is arranged above the hydroponic box for light supplementing, so that the difference between the light intensities of different cultivation positions in the whole hydroponic box is not more than 5%.

5. The method for evaluating the precise salt tolerance of rice by using spectrum according to claim 1, characterized in that, The light supplementing method is as follows: taking the size of the culture rack on which the hydroponic box is placed as an example, 1 m in length and 0.5 m in width, two tissue culture lamps with the same spacing are installed on the top of the culture rack, one lamp is installed at a position 15 cm below the top lamp tube before and after the culture, and two lamps are vertically installed at positions 10 cm and 40 cm in the width direction on the left and right sides, respectively, to supplement light to different areas in front, back, left and right; at the same time, silver reflective cloth is installed at the front and back positions of the culture rack to completely block the reflection in front and back.

6. The method for evaluating the precise salt tolerance of rice by using spectrum according to claim 1, wherein, In the step (2), the spectrum of the marked leaf is measured one day before the salt treatment and five days after the salt treatment, and the change amount of the spectrum index is calculated.

7. The method for evaluating the precise salt tolerance of rice by using spectrum according to claim 6, characterized in that, The calculation formula of the dead seedling rate and the change amount of the spectrum index is as follows: Dead seedling rate = -109.714x + 100.628, x is the change amount of the spectrum index one day before the salt treatment and five days after the salt treatment.

8. The method for evaluating the precise salt tolerance of rice by using spectrum according to claim 1, wherein, In the step (2), a handheld plant reflectance spectrum measuring instrument is used to measure the spectrum.

9. The method for evaluating the precise salt tolerance of rice by using spectrum according to claim 1, characterized in that, In the step (2), the spectrum measurement position is the middle position of the length of the marked leaf, and the time for measuring the leaf spectrum each time is from 15:00 to 18:00; after the rice seedlings grow to the two-leaf-one-heart stage, the Yoshida nutrient solution with a NaCl mass concentration of 0.8% is used for treatment.

10. Use of the method according to any one of claims 1 to 9 for evaluating salt tolerance and / or predicting seedling mortality rate in salt tolerance experiments of rice germplasm.

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