Pots Test Varieties: Bailv9, Bailv11, Bailv935, Bailv985.

Field Test Varieties: Bailv9, Bailv11, Bailv935, Bailv985, Bailv12, Bailv10, Bailv8, Bailv6, Bailv14, Bailv15, Bailv522, Zhonglv5, Zhonglv8, Zhonglv11, Jilv03083, Liaolv8, Liaolv3, Tonglv918, Jilv7, Jilv9.

The seeds used in the experiment were provided by the Edible Bean Research Institute of Baicheng Academy of Agricultural Sciences. Nitrogen fertilizers (urea containing 46%N), phosphate fertilizers (superphosphate containing 12% P₂O₅) and potassium fertilizers (potassium sulfate containing 50% K₂O) were purchased from Sinochem Jilin Changshan Fertilizer Co., Ltd. (Songyuan, Jilin Province, China).

The experiment was conducted at the Baicheng Academy of Agricultural Sciences in Jilin Province during May to September in 2017 - 2018. Baicheng City (123˚ east longitude, 45˚ north latitude) has a temperate semi-arid continental monsoon climate. During the 2017 - 2018 test years, the average rainfall from May to September in the crop growing season was 404.93 mm, the average daily temperature was 20.03˚C, and the average sunshine duration was 1243.2 hours . At the growth periods of the trails in 2017 - 2018, the temperature and sunshine duration were not affected yield production, with the proper management. During the flowering stage of July 2017 and August 2018, there was less rainfall than there had been in previous years. Consequently, irrigation was applied once in July 2017 and in August 2018.

The soil type is chernozem (pH = 7.5) with a layer thickness of about 15 mm. The soil layer organic matter content was 2.21%, total nitrogen content was 0.19%, total phosphorus content was 0.14%, and total potassium content was 1.93%, of which available nitrogen was 120 ppm, available phosphorus was 82 ppm, and available potassium was 140 ppm.

Water treatment 1 (X₀): 3 times of water stress treatment after severe wilting at flowering stage (3 times of rehydration); Water treatment 2 (X₁): 5% PEG6000 water stress treatment after 1 - 2 times of normal irrigation; X₀ and X₁ were water stress treatments.

Water treatment 3 (X₂): 3 times of normal irrigation, with normal plant growth and development as the water control standard; Water treatment 4 (X₃): irrigated in case of drought, 2 - 3 times more water than the normal irrigation X₂ treatment, simulating a climate with more rainfall condition. X₂ and X₃were non-stress treatments. The water in the four treatments (X₀, X₁, X₂, and X₃) and control was increased sequentially.

Drought stress treatment: 1) 3 times of drought stress treatment (3 times of rewatering) were carried out at the beginning of flowering, full flowering and pod setting. The drought conditions were recorded when severe drought was encountered during the flowering period, and the leaves were wilted for two consecutive days in the afternoon and then rehydrated. At each rewatering time, 80% of the leaves of the plants began to wilt, but before they curled and fell off, the water supply was 100%.

2) Natural drought conditions in the field, select plots without irrigation conditions.

Fertilizer treatment: treatment F120 (F1): optimized fertilization method of N:P:K = 1:0.55:1.16; treatment F100 (F2): for conventional fertilization, the ratio of N, P and K was 1:1.18:0.94; treatment F50 (F3): reduced fertilization, and the amount of fertilizer was reduced by half compared with treatment F100; treatment F0 (CK): no fertilization ( Table 1 ).

The open-air cultivation potted experiments were conducted, and a cylindrical plastic pot was used, the bottom diameter was 25 cm, the mouth diameter was 30 cm, and the height was 38 cm. Ordinary field soil was used, the same amount of soil was loaded into each pot, watering was performed before sowing, and seedlings were thinned after emergence, leaving 8 seedlings in each pot. Four levels of fertilizer treatments and four water treatments were performed on each variety. A completely randomized design was used with 3 replicates. The rest of the time is managed normally to ensure that there is no excessive drought and growth and development are not seriously affected. Sampling at the full blooming stage for investigation and statistics of fertility traits; yield testing at the mature stage.

The yield changes of mung bean varieties Bailv9 and Bailv11 were test under X₀, X₁, X₂, X₃ water regimes respectively, to calculate the water stress sensitivity index and drought resistance coefficient, and to analyze the sensitivity and drought resistance of mung bean varieties [28] . Also, the interactions effects of water regimes and fertilization modes were tested, to evaluate the optimal fertilization performances compared with other fertilization modes under each water water treatments. Moreover, the mung bean varieties of Bailv9, Bailv11, Bailv935, Baiv985 were used to investigate the optimal fertilization responses in drought stress condition. The formula for calculating the water stress sensitivity index (Di) was as follows:

Di = (1 − Yd/Yp)/(1 − sum Yd/sum Yp)

where Yd is the yield (trait value) under water stress, and Yp is the yield without water stress (trait value). The drought resistance coefficient (Dc) is typically an important indicator for measuring the drought resistance of crop varieties and is calculated as follows:

Dc = Yd/Yp

where Dc and Di are negatively correlated with each other.

Variety identification test under natural drought conditions in the field. The proven and effective optimized fertilization treatment in pots was adopted, and 20 varieties of mung bean and red bean were tested under natural drought in the field. The field area was 4 m² and the plant spacing was 15 cm. Each cultivar was treated with 2 levels (F0 and F120) of fertilizer in a split-plot design with 3 replicates.

And set up a rain shelter, which is conducive to moisture control and eliminates the influence of rainfall. The rest of the time is managed normally to ensure that there is no excessive drought and growth and development are not seriously affected. Sampling was carried out at the full flowering stage to investigate the fertility traits, and the yield was uniformly measured at the mature stage.

Plant height: The height from the cotyledon node to the point where the petiole of the last compound leaf of the main stem is attached (apex). Number of main stem nodes: the number of nodes from the cotyledon node to the last compound leaf-bearing node at the top of the plant. Root dry weight: Randomly take all the root systems of 5 plants, weigh the fresh weight centrally, and calculate the average value. Then air dry or weigh after oven drying to calculate dry weight. The error is not more than 0.5 g, and the unit is expressed in g. Stem dry weight: All the stems of 5 plants were randomly taken, and then weighed after drying in the oven, and the dry weight was calculated. The error is not more than 0.5 g, and the unit is expressed in g. Number of pods per plant: 5 plant samples were randomly taken from each plot, and the average number of pods per plant was calculated. Number of seeds per pod: The number of seeds per pod was calculated by randomly counting the seeds in ten mature pods using the average number of seeds. Hundred seed weight: 100 seeds were weighed, repeated 3 times, and the average weight was calculated. The error is not allowed to exceed 0.5 grams, expressed in g. Plot yield: All mature plants within 6 m² (two rows of 5 m long) were taken from each experimental plot, and the pods were harvested manually. When the harvested grains were dried to less than 13% moisture, the plot yield was measured by weighing and expressed in kg. It is then converted into hectares of yield. Randomly select 5 single plants and excavate them with their roots, rinse with water to remove the soil from the roots, put them in a cool place to air dry and weigh the fresh weight, and calculate the average value, in g. Randomly take the root system of 5 individual plants, measure the length of the main root, and take the average value in cm.

Excel was used for raw data processing and analysis, and table preparation; DPS was used for significant variance analysis, and P < 0.05 was considered significant difference.

As shown in Table 2 , the average water sensitivity indexes of the main morphological

Note: Water stress sensitivity index Di = (1 − Yd/Yp)/(1 − sum Yd/sum Yp), Yd was the yield of water stress (trait value), Yp was the yield of non-water stress (trait value), Dc = Yd/Yp was the drought resistance coefficient, and Ddc was negatively correlated with Di.

indicators of Bailv9 were in the following order: chlorophyll content > plant height > 100-grain weight > fresh stem weight > pod number per plant > lateral root number > plant fresh weight > main stem branch > leaf fresh weight > root fresh weight > single pod number of grains > the yield; the average water sensitivity coefficients of the main morphological indicators of Bailv11 were in the following order: yield > 100-grain weight > main stem branch > number of pods per plant > root fresh weight > stem fresh weight > plant Fresh weight > fresh leaf weight > number of seeds per pod > number of lateral roots > plant height > chlorophyll ( Table 2 ). The water sensitivity and drought resistance index of Bailv9 were Di = 0.89 and DC = 0.79; and Bailv11 had a Di of 1.76 and DC of 0.59 , these results indicated that Bailv9 was not sensitive to water, and its drought resistance was significantly stronger than that of Bailv11 ( Table 2 ).

Bailv9 and Bailv11 were sensitive to fertilization effects, the yield increased under stress conditions compared with no fertilization condition. The yield of Bailv9 increased under the stress conditions in the order of F0 (ck), F120 (39.34%) > F100 (26.39%) > F50 (26.21%), with fertilizer efficiency sensitivity index of Di = 1.21; the yield of Bailv11 increased under stress conditions in the order of F100 (29.88%) > F120 (28.04%) > F50 (22.75%), with the fertilizer efficiency sensitivity index of Di = 0.71; The sensitivity index of fertilization effect was Bailv9 > Bailv11 ( Table 3 ). Under non-stress conditions, the three fertilization treatments of Bailv9 had an increased yield compared with no fertilization F0 treatment, in the order of F50 (28.50%) > F120 (23.77%) > F100 (10.17), with the fertilizer efficiency sensitivity index of Di = 0.91; each fertilization treatment increased the yield of Bailv11, compared with no fertilization F0 treatment by order of F120 (45.37) > F100 (36.00%) > F50 (18.15%), with the fertilizer efficiency sensitivity index of Di = 1.05; the two varieties were sensitive to fertilization effect in order of Bailv11 > Bailv9. Under non-drought conditions, the halved fertilization mode of mung bean increased yield by 23.52%, compared with no fertilization, and the yield increase was smaller than that under drought conditions ( Table 3 ).

The optimized fertilization model increased the yield of Bailv9 and Bailv11, by 33.37% and −6.98% respectively, compared with that for F100 under stress conditions, and the effects of optimized fertilization increased the yield of Bailv9 and Bailv11 by 57.21% and 20.65% respectively, compared with F100 under non-stress conditions. The above test results further illustrated that the varieties with stronger drought resistance not only had a significant yield increase under non-stress conditions; even under stress conditions, the optimized fertilization mode could still be more effective than conventional fertilization. There was a large yield increase effect, and it was more cleared that the yield increase of the optimized fertilization mode was very significant ( Table 3 ).

The highest yields of mung bean varieties Bailv9 and Bailv11 all appeared in the F120 fertilization mode, and Bailv9 had higher yields in the two treatments of F120X1 and F120X2. The yield of Bailv11 was higher in both treatments F120X1 and F120X2. In addition, the yield of Bailv9 for each fertilization treatment were ranked in order of F120 > F50 > F100 > F0; the yield of Bailv11 were in order of F120 > F100 > F50 > F0. Under different water treatments, the yields of the two mung bean varieties showed a trend of first increasing and then decreasing with the increase or decrease of the water gradient; and mung bean yield were significantly higher than the control (X0). The yield differences among the water treatments were significantly greater than the yield differences within the water treatments due to the different fertilizer treatments ( Table 3 ).

As shown in Table 4 , the results of correlation analysis between various trait indicators and yield results showed that the correlation coefficients between mung bean yield and various plant traits and yield components were as follows: the number of pods per plant (r = 0.70**) > the number of lateral roots (r = 0.0.57**) > the number of nodes in the main stem (r = 0.54**) > the number of grains per pod (r = 0.49**) > the main stem branch (r = 0.44**) > Main root length (r = 0.43**) > chlorophyll content (r = 0.42*). The correlation coefficient between the number of pods per plant and other characters were in the order of yield (r = 0.70**) > number of lateral roots (r = 0.61**) > number of nodes in main stem (r = 0.59**) > chlorophyll content (r = 0.59**). The correlation coefficients between the number of grains per pod and other traits were in the order of number of main stem nodes (0.68**) > chlorophyll content (r = 0.59**) > yield (r = 0.49**) > main stem branches (r = 0.47 **) > plant height (r = 0.46**). The correlation coefficient between 100-grain weight and other traits were plant height (0.57**) > chlorophyll content (r = 0.53**) > main root length (r = 0.42*) > main stem node number (r = 0.42*). The size of the correlation items among other traits of mung bean were shown in Table 4 .

Note: *P < 0.05, **P < 0.01.

As shown in Table 5 , the correlation coefficients between the yield of mung bean and various morphological indicators were in the order, root fresh weight (r = 0.69**) > stem fresh weight (r = 0.59**) > stem dry weight (0.57**) > fresh weight of plants (r = 0.56**) > dry weight of plants (r = 0.54**) > ratio of root to shoot (0.48**) > fresh weight of leaves (r = 0.43*) > dry weight of roots (0.37*). The correlation coefficients between plant fresh weight and other morphological indicators and yield were stem fresh weight (r = 0.99**) > leaf fresh weight (r = 0.95**) > root fresh weight (0.89**) > yield (r = 0.56 **) > plant dry weight (r = 0.45**) > leaf dry weight (r = 0.43*) > stem dry weight (0.43*). The order of correlation coefficient between root fresh weight and other traits were plant fresh weight (r = 0.89**) > stem fresh weight (r = 0.88**) > leaf fresh weight (r = 0.81**) > yield (r = 0.69**) > plant dry weight (0.537**) > root/shoot ratio (r = 0.53**) > leaf dry weight (r = 0.51**). The correlation coefficients between other traits were shown in Table 5 .

Note: *P < 0.05, **P < 0.01.

Under the condition of potted drought stress, the response results of various mung bean varieties under different fertilization modes showed that the plant height, main root length, main stem node number, and the yield of Bailv9, Bailv11, Bailv935, and Bailv985 were all equal. The best performance was under F120 (optimized fertilization mode), and the difference was significant compared with other treatments (P < 0.05). Compared with other treatments, the difference was significant (P < 0.05), while the fresh weight of Bailv985 was not the best in F120, and the difference was significant compared with F0 and F50. There was no significant difference (P > 0.05) with the conventional fertilization treatment F100 ratio. The chlorophyll content of each variety was the best under the condition of F120, and was significantly (P < 0.05) higher than that of F0 and F50, but had no significant difference compared with conventional fertilization treatment F100. Under different fertilization conditions, the root-shoot ratio of Bailv9 was F0 > F50 > F120 = F100. The condition was significantly (P < 0.05) higher than other treatments; the effect of different fertilization on the root-shoot ratio of Bailv11 and Bailv935 was F0 > F50 > F120 > F100, and there was no significant (P > 0.05) difference between F50 and F120 on Bailv11 , and the ratio of F0 was significantly different; F50, F100 and F120 had no significant(P > 0.05) effect on Bailv935, but had a significant difference with F0; the response of the root-shoot ratio of Bailv985 under different fertilization conditions was, F0 > F120 > F50 > F100, and the performance of F50, F120 and F100 were not significantly different, but significantly different from F0 ( Table 6 ). Compared with the mung bean varieties treated with F50, F100, and F120, the yield of Bailv9 increased by 56.20%, 81.27%, and 107.22%, respectively; compared with that of F0, the yield of Bailv11 increased by 10.18%, 19.42%, and 45.88%, respectively; Bailv935 increased by 26.52%, 61.90%, 74.16% respectively, and Bailv985 increased by 23.78%, 56.92%, 87.62% respectively ( Table 6 ).

Note: F0 is no fertilization, F50 is half of conventional fertilization, F100 is conventional fertilization, and F120 is optimal fertilization.

Under the conditions of field drought stress, the yield of each variety with optimized fertilization treatment increased significantly compared with the control non-fertilization. In addition, among the 20 mung bean varieties treated with F0 and F120, the plant height, main root length, main stem node number and plant fresh weight of each variety treated with F120 showed significance (P < 0.05) or extremely significance (P < 0.01) compared with control treatment performance. Compared with the control treatment, the plant height of Liaolv8 and Jilv 9 increased the most, with an increase of 107.14% - 105.46%, respectively; the main root length of Zhonglv5 and Bailv14 increased the most, with an increase of 164.42% and 109.78% respectively; the number of main stem nodes of Zhonglv11, Liaolv3 and Jilu7 increased the most, increased by 81.43%, 76.14% and 76.37%, respectively. The fresh weight of plants of Zhonglv11, Liaolv3 and Liaolv8 increased significantly, which increased by 404.34%, 832.99% and 522.22%, respectively. The root-shoot ratio of each mung bean cultivar was significantly lower under the F120 condition, and the response under the F0 condition, which may be due to the significant increase in the root-shoot ratio under drought stress. There was no significant difference in the increase in the root-shoot ratio of F120 of each variety compared with the control ( Table 7 ).

Note: CK was non-fertilization, F120 was optimal fertilization.