Soybean [Glycine max (L.) Merr.] is one of the most important vegetable and oilseed crops with an annual value of over 36 billion dollars in the U.S. Soil Zn deficiency can reduce soybean yield and quality; therefore identifying Zn efficient genotypes can offer a sustainable solution to this problem. Furthermore, a reliable method for screening soybean lines would be useful for breeders. The main objective of this study was to detect genotypic variation in soybean under low Zn stress. This was accomplished by using physiological variables including biomass, leaf area, chlorophyll content, stomatal conductance, and shoot nutrient concentration. Ten soybean genotypes were subjected to low Zn availability (1 pM) with chelate buffers in hydroponics. Visual symptoms of Zn deficiency were evident at 21 to 28 d after treatment. Compared to sufficient Zn, low Zn conditions significantly affected four of ten genotypes. Additionally, low Zn reduced leaf area, chlorophyll, shoot Zn, and Fe concentration. The genotypes that proved more Zn efficient were “Williams” and “Pella86”. These genotypes had higher leaf area, chlorophyll, and leaf nutrient content such as Zn and N. This research demonstrated considerable genotypic variation among soybean genotypes that may be selected for Zn efficiency based on a hydroponics screening. More Zn efficient genotypes identified in this study may be used to prevent field yield losses where soil low Zn availability is a problem.

Understanding how plants respond to low Zinc (Zn) is important, as Zn deficiency is a major factor affecting crop productivity throughout the world. Selection and breeding of plants for Zn efficiency, which is defined as the ability to maintain reasonable yield under Zn deficiency, is a useful approach to increase production and quality on low Zn soils. Hydroponic experiments were conducted to investigate the responses of two bean cultivars (Phaseolus vulgaris L. cvs. Calima and Jamapa) to differential Zn conditions. Bean seedlings were grown in a chelate buffer nutrient solution and exposed to low and sufficient Zn conditions. Plant height, taproot length, final shoot and root fresh weight, leaf symptoms, chlorophyll content, and leaf area were recorded for up to 28 days. Leaves of different sizes were collected from plants and leaf area was determined by a leaf area meter. The results showed that shoots and leaves are most likely the key sites for Zn efficiency trait in bean. Furthermore, the results also showed that total leaf area may be a potentially useful tool that correlated with Zn efficiency in common bean. Overall, cv. Calima was highly resistant, while cv. Jamapa was very susceptible to Zn stress. The susceptible cv. Jamapa displayed a decreased shoot biomass, root biomass, chlorophyll content, and leaf area under low Zn conditions. This study demonstrated that leaf area permitted the discrimination of Zn-efficient and Zn-inefficient bean lines. Therefore, measurement of leaf area may provide a useful indirect criterion for screening of Zn efficiency in bean.