Field Crop 2025, Vol.8, No.3, 126-138 http://cropscipublisher.com/index.php/fc 133 stable, with an increase of about 10% compared to the control medium, Huang 13. However, "Jindou 40" is a bit inferior, only 80% of the comparison. Drought-resistant varieties like Silihong and Suinong 28 have a yield reduction of less than 15%, but sensitive types such as Jiyu 86 may experience a drop of over 30% in drought (Asfaw et al., 2009; Belay et al., 2019). Other beans are more or less the same. Among the peas, "Qinghai 13" can still have an 85% yield in a drought year, while some varieties only have a 60% yield. We also found that the interaction effect between varieties and the environment is quite obvious: some varieties grow well everywhere and belong to the widely adaptable type; some are particularly picky about the location. For instance, there is a new variety of mung bean that performs outstandingly in the arid regions of Inner Mongolia, but in the more humid areas of Henan, it is just so-so. This interaction effect can explain 30% to 40% of the variation. It can also be seen from the GGE chart that the most suitable varieties for different regions are actually not the same (Dadras et al., 2017). There is no "universal variety" that is strong in everything. Although the influence of the environment accounts for more than half, the output can still be increased through variety and regional matching. In conclusion, when breeding, it is best to select drought-resistant varieties based on different ecological regions. Of course, widely adaptable varieties may become increasingly useful in the future, after all, the weather is unpredictable. 6.2 The contribution of key traits to yield performance Based on our field observations and data analysis over the past few years, there are indeed significant differences in drought resistance among different varieties. For instance, in terms of root systems, varieties with deep roots and large root mass usually have higher yields. For example, the root dry weight of the soybean "Si Li Hong" is 25% higher than that of "Ji Yu 86", and the leaves remain green and the grains are plump as well. The water retention capacity of leaves is also very important. Under drought conditions, leaves with a higher relative water content (RWC) tend to maintain better yields. The leaf temperature of drought-resistant varieties is usually slightly higher, indicating that the stomata close earlier and save water. In terms of photosynthetic and water use efficiency (WUE), varieties with less decline in photosynthetic rate naturally have more stable yields. This type of variety generally maintains good chlorophyll and has a high WUE. In addition, drought-tolerant individuals generally accumulate a large amount of proline and soluble sugar, have high antioxidant enzyme activity, and suffer less membrane damage. Overall, deep root systems, good water retention, high WUE and strong oxidation resistance are common features of drought-resistant varieties. By using the root-crown ratio, chlorophyll retention rate and proline content for discrimination, nearly 90% of the varieties can be correctly classified. These rules are quite consistent in legumes and should have good reference value for material selection in breeding. 6.3 Comparison with existing research and breeding objectives Compared with previous research and breeding goals, our results this time have both similarities and differences. For instance, the soybean variety "Handou 13" has increased production by approximately 10% compared to Zhonghuang 13, which is close to the performance of the widely applicable varieties that have been reported. The drought resistance of the pea variety "Qinghai 13" in the dry land of the plateau has also been verified. In terms of drought tolerance mechanisms, features such as deep root systems, good water retention, high water use efficiency and strong antioxidant capacity are indeed crucial, which is consistent with some previous conclusions (Islam et al., 2022; Xu et al., 2023). However, some different situations have also been found. For instance, some mung bean varieties are drought-tolerant during the seedling stage, but suffer from severe drought during the reproductive period, indicating that the entire growth period should be examined. There are also some varieties that belong to the "tolerant type", with good leaf green maintenance but not necessarily high yield. Some other "avoidant" types avoid drought by maturing early, resulting in more stable yields. These results not only verify the existing understanding but also provide some new basis for drought-resistant breeding. 7 Suggestions for Agronomy and breeding Applications 7.1 Target environment zoning and variety recommendation scheme Based on the performance of the varieties in rain-fed environments, the dryland farming areas in the north can be roughly divided into three categories, and the corresponding varieties are recommended. For instance, in semi-arid areas like Horqin in Inner Mongolia, where the annual rainfall is 300 to 400 millimeters and spring drought is
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