Field Crop 2025, Vol.8, No.3, 126-138 http://cropscipublisher.com/index.php/fc 132 "Shengyu 6" also approaches this ideal characteristic. The situation of other beans is similar. Two pea varieties have been quite stable for two years, with CVS both below 10%. However, there is a new variety of mung bean that has a high yield when there is good rainfall, but it drops significantly when there is a drought, with a CV exceeding 25%. These analyses help us clearly understand the adaptability types of the varieties and are very helpful for breeding varieties that are both high-yielding and stable in yield (Rao et al., 2023). 5.2 Index calculation and trait association analysis To compare the drought resistance of different varieties, we used several indices, such as DSI, TOL, MP, GMP and STI, and also conducted correlation and principal component analyses. For instance, for soybeans, a DSI lower than 1 indicates good drought resistance and less yield reduction. A small TOL is often drought-tolerant but the yield may not be high. MP, GMP and STI simultaneously reflect output and stability. The correlations among these indicators are very strong. In peas, STI is highly positively correlated with GMP (r=0.98), while negatively correlated with DSI (r≈-0.85) (Ryabukha et al., 2023). Principal component analysis revealed that the first two principal components accounted for over 90% of the variations. PC1 was mainly determined by STI, GMP and MP, while PC2 was negatively correlated with DSI (Rehman et al., 2019). The results sorted by PC1 are basically consistent with the actual yield performance in the field. Regression analysis indicated that the chlorophyll retention rate, root dry weight and proline content of soybeans could jointly explain approximately 85% of the yield changes. The survival rate of pea seedlings and the relative water content of leaves during the flowering period were significantly correlated with the yield (r approximately 0.77 and 0.72). The relative germination rate of mung beans during the germination period is also correlated with the yield reduction rate (r=0.68) (Morovati and Kordenaeej, 2021). From the perspective of coefficient of variation, the CV of yield under drought conditions is approximately 20%, while the cumulative CV of proline reaches 40%, indicating a higher degree of differentiation. Overall, varieties with good drought resistance generally have the characteristics of low DSI, high STI and strong green retention. These indicators can provide a basis for drought-resistant breeding. 5.3 Water use efficiency and crop model simulation Under drought conditions, water use efficiency (WUE) often becomes the key to stable production. However, the differences among various varieties are quite obvious. First, we estimate the WUE by combining the output and actual water consumption, and then use the model to examine the long-term performance. The calculation mainly uses the Penman-Monteith model and the measured evapotranspiration data to obtain the grain WUE. The results are quite intuitive: In Gansu Province, some soybean varieties consume approximately 400 liters of water to produce 1 kilogram of seeds, while the control variety consumes more than 500 liters (Park et al., 2014). The results of gas exchange are similar. The A/T ratio of drought-tolerant varieties is generally higher, indicating that water usage during photosynthesis is more cost-effective. On the model side, after calibration with CROPGRO, 20 years of meteorological data were input to run the simulation. The results show that in particularly dry years, drought-resistant varieties may suffer a reduction in yield of approximately 15%, while the control varieties may drop by more than 30% (Bulacio et al., 2023). It is worth noting that if the climate continues to warm up, the yield reduction of those drought-tolerant varieties will be more moderate due to their earlier closure of stomata and lower evaporation. The simulation also reminds us that the upper limit of yield is mainly determined by the water that the environment can provide, but drought-tolerant varieties are more likely to approach this upper limit. For instance, when the annual rainfall is 300 mm, drought-resistant soybeans can yield 1.8 tons per hectare, which is close to 90% of the potential, while common varieties only have about 1.5 tons. From the comparison of the measured and simulated results, it can be seen that both point to one conclusion: drought-resistant varieties are more water-efficient and efficient, which can be regarded as a very practical basis in variety screening (Silva et al., 2022). 6 Results and Discussion 6.1 Analysis of inter-species differences and genotype-environment interactions After field trials, it was found that the yields of different legume varieties vary quite a lot under drought conditions where they rely on the weather. For instance, regarding soybeans, the average yield of the three sites over the past two years ranged from 1.3 to 2.2 tons per hectare. "Handou 13" performed the best and was the most
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