Miranda Ruth and Bryan Hopkins, Department of Plant and Wildlife Sciences
Plants uptake iron from the soil in a variety of ways. Dicots, like soybeans, primarily exude hydrogen (H+) ions and chemical reductants from their roots, which acidify the root zone and reduce Fe3+ to Fe2+ that can then be utilized by the plant (Brown and Jolley 1989). Iron efficiency in soybeans results in increased dietary iron for those eating the beans. Anemia, which is due to a dietary lack of iron, is an extremely serious health problem that affects much of the world, especially developing countries. Globally, over 30% of the world suffers from this lack of dietary iron; in Africa, for example, 68% of preschool aged children are anemic (WHO Global Database 2015). This project aims to compare common soybean varieties in terms of iron-efficiency and actual iron content in yield. The soybean varieties selected could be chosen for growth in different countries depending on regional soil type, soil quality, and climate. By introducing an iron-efficient legume into their garden or crop rotation, farmers and families would be able to better meet their dietary nutritional requirements. This research would expand the potential for systems of urban agriculture in developing countries and could be implemented to improve overall health.
We will grow and compare two soybean varieties of unknown iron-efficiency used in Malawi, the country I spent my summer researching in. The varieties are called Makwacha and Tikolore. The soybean seeds of each variety will be first grown in separate hydroponics systems in our environmentally controlled lab growth chamber for approximately 23 days. The nutrient solution that the roots will be immersed in will be an alkaline nutrient solution, as used by Terry et al. (1991). Each variety will have a +Fe and a –Fe treatment to detect an iron-stress response. Once established, plants will be visually rated for chlorosis and solution pH, and root reduction of iron will be measured approximately every other day. This will allow us to determine each variety’s iron-efficiency, because an increase in H+ ions at the root indicates an iron-stress response, and therefore lowers the solution pH. Root biomass, shoot biomass, and iron concentrations will be measured at the end of the study.
- Both varieties interestingly lacked an iron stress response in terms of pH
- Results were not graphed because no statistical differences in pH between the +Fe and –
Fe treatments were observed
Visual Chlorosis (Fig.1
- -Fe treatments showed significantly higher rates of iron chlorosis than +Fe for both
Makwacha and Tikolore varieties
Dry Weights (Fig.2)
- Both -Fe shoots and roots had significantly lower biomass weights for Tikolore variety,
but this was not observed in Makwacha variety
Both Makwacha and Tikolore varieties seem to lack an iron-stress response in terms of pH. However, the plants clearly show visual signs of an iron-stress response. Makwacha variety showed no statistical differences in root and shoot biomass, suggesting that growth is not significantly inhibited by iron stress. However, evident iron chlorosis will most likely affect the quality of the crop yield. Growth in Tikolore variety was shown to be significantly inhibited by an iron-stressed environment. Further studies would include testing these Malawi soybean varieties against a variety that is well adapted to alkaline soils that most likely has a known ironstress response. Also, testing for concentrations of iron reductant in the nutrient solution could determine whether or not either of these two varieties exhibit an iron-stress response at the roots.
This project serves as a great diagnostic study for further research about these two varieties in Malawi. They are both commonly grown throughout the country, but nothing is known regarding their iron-efficiencies. Growing them hydroponically again could continue this study and comparing them to a North American soybean variety like the A203, that has a known iron-stress response. Also, you could measure for the concentration of chemical reductants at the roots to give a quantifiable iron-stress response for each of the varieties, even though they didn’t seem to exude Hydrogen ions. This project has a fair amount of future value as it could identify which of these two varieties should be grown in poor nutrient soils and iron-deficient soils in the Malawi regions in order to get better crop and dietary nutrition.