By Silvina Arias, Adjunct Assistant Professor Plant Pathology, Entomology and Microbiology, ISU

Project Collaborator:

• Jamie O’Rourke, Research Geneticist, Agronomy

Project Summary

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.

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. 

This study will be performed using hydroponic systems. Hydroponic systems have been shown as an effective means to mimic iron availability problems in Iowa and Minnesota fields. This controlled system allows researchers to study genetic variations and evaluate phenotypes while strictly controlling Iron availability without confounding factors such as soil texture, moisture content, and pH. 

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.

In summary:

• We will compare iron stress-Fusarium stress phenotypes and gene expression patterns between genotypes for each treatment. 
• We will identify clusters of genes with similar expression patterns. 
• We will attempt to assign the biological roles to the gene clusters -related to defense, iron homeostasis, cell cycle, and gene silencing and photosynthesis.

Additional Information

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. 

(1-year project funded fall 2023)