| Iron-Deficiency Chlorosis (IDC) causes yield losses in soybean and other crop species as a result of the plant's inability to efficiently acquire iron from calcareous soils. Although plants differ in their response to iron deficiency and IDC resistance has been improved in soybean, the biology of IDC is not well understood. We undertook an interdisciplinary approach towards increasing our knowledge of IDC resistance and iron acquisition strategies in higher plants. Firstly, we examined the usefulness of molecular markers to improve breeding efficiency for IDC resistance in soybean. After examining Simple Sequence Repeats (SSR) markers genetically linked to previously identified quantitative trait loci for IDC resistance in a soybean breeding population, we determined that SSR marker Satt481 may improve selection efficiency 2.6-fold and reduce the evaluation costs by 70% relative to traditional breeding approaches. Secondly, we investigated the potential relationship of IDC with Soybean Cyst Nematode (SCN) and calcareous soil properties. Using two soybean breeding populations and fourteen soybean genotypes grown on calcareous soils infested with Heterodera glycines and concurrent greenhouse studies, we were not able to establish a consistent relationship between IDC-related chlorosis and SCN. However, an increase in foliar chlorosis in SCN-susceptible genotypes was associated with a decrease in SCN reproduction, and SCN-resistant genotypes were more susceptible to IDC during greenhouse evaluation relative to evaluation on SCN-infested calcareous soils. In addition, calcareous soil properties predicted foliar chlorosis in only one breeding population evaluated on SCN-infested soils during one year. Lastly, we examined the evolution of Strategy I and II mechanisms for iron acquisition in higher plants. The phylogenetic distribution in plants of nine iron acquisition-related genes for both strategies was determined using Expressed Sequence Tags (ESTs) from eleven plant species (one gymnosperm, five dicots, and five grasses). Our results suggested gene conservation across strategies and Strategy II was more recently derived than Strategy I in higher plants. In our studies, we have further demonstrated the complexity of IDC, while increasing knowledge on the biology of IDC and iron acquisition using an interdisciplinary approach involving methodologies in classical and molecular genetics, plant pathology, and soil science. |
