Iron deficiency chlorosis (IDC) is the symptom typically observed in soybean growing in high-pH soils with high carbonate concentrations where iron availability is reduced. Currently, the most important management option is the selection of ID-resistant cultivars. Several studies have detected QTL that confers resistance to IDC.
Other limitations on soybean production are due to soybean diseases that reduce yield. Several species of Fusarium are well recognized as soybean pathogens, such as F. virguliforme, the causal agent of sudden death syndrome (SDS), F. oxysporum causing Fusarium wilt or F. graminearum, a major necrotrophic pathogen causing severe root rot. F. graminearum also is the most frequently recovered species of Fusarium in fields in Iowa. Management of soil-borne diseases like Fusarium root rot depends mainly on genetic resistance or seed treatments during emergence and the seedling stages. Soybean resistance to F. graminearum was described in the soybean cultivar Conrad, and putative Quantitative Trait Loci (QTL) associated with resistance to F. graminearum were.
Although soybean plants with IDC symptoms often display Fusarium root rot symptoms, currently the basis of this association is not clear. In general, research programs focus on identifying resistance to a particular stress and do not test susceptibility to other biotic or abiotic stresses. Consequently, improved varieties may respond unpredictably when grown in field conditions.

The objective of this study is to characterize soybean genes that are differentially regulated by the host during F. graminearum infection in an iron deficiency environment in order to identify new potential resistant mechanisms and candidate genes involved in the defense response.
Our specific objectives are to:
1. Evaluate phenotypically IDC-resistant and susceptible soybean cultivars inoculated with F. graminearum under iron deficiency conditions in a hydroponic system.
2. To elucidate the comprehensive gene expression in response to the pathogen and iron deficiency simultaneously (RNA seq analysis).
3. Identify, compare, and analyze differentially expressed genes.

To our knowledge, transcriptional changes in soybean roots that have been infected by F. graminearum growing in an environment with low iron availability have not been studied.
The finding generated will be useful for determining environmental conditions and stress factors on the epidemiology of soilborne pathogens that affect seedlings and taking steps toward identifying effective management. In addition, these results may be useful in developing new methods of broadening the resistance of soybean to F. graminearum and iron deficiency.

Updated October 1, 2024:
To characterize genetically the soybean response to abiotic stress (iron deficiency) and biotic stress (F. graminearum-FG infection), first, we worked on the optimization of a screening method to evaluate simultaneous stress effects in a hydroponic system. We standardize the response of soybean near-isogenic lines Clark (PI548553, iron efficient) and IsoClark (PI547430, iron inefficient) under combined iron deficiency+ Fg inoculum conditions. Three weeks after planting, the growth parameters and chlorophyll content were measured. Detailed root morphological and architectural measurements will be analyzed by WinRHIZO root-scanning software.
The RNA extraction was realized from root and leaf tissues using Qiagen RNeasy and Min-Elute kits. After running the quality checks on the samples, they will be submitted to the Iowa State University DNA Facility for library construction and sequencing (RNA seq). The bioinformatic analysis will allow us to identify, compare, and cluster differentially expressed genes between roots and leaves within each genotype for each treatment.

A 3-month no cost extension was granted on the project to complete sample processing.

Results may be useful in developing new methods of broadening the resistance of soybean to F. graminearum and iron deficiency.