Leonardo Rocha

Southern Illinois University Carbondale
Advised by Dr. Jason Bond and Dr. Ahmad Fakhoury

Exploring the suppression of soybean cyst nematode (Heterodera glycines Ichinohe) populations by wheat through a multi-omics approach

The soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) is the major plant-parasitic nematode affecting soybean production throughout Illinois. SCN is estimated to be present in more than 80% of Illinois fields and in every county. SCN causes losses of up to 60% in susceptible cultivars, and often losses of up to 30% occur without showing noticeable aboveground symptoms. In South-Central Illinois, soybeans are commonly planted in fields following winter wheat harvest in mid-to-late June in a double-cropping system. A series of field trials were conducted to investigate the effect of wheat on SCN populations in double-cropping soybean. Wheat was planted in strips alternating with strips-maintained weed-free and under fallow over winter and early spring. Soybean was planted in all strips after the wheat harvest. SCN egg densities were acquired at four-time points: wheat establishment, post-wheat/pre-soybean, mid-soybean (R1 stage), and post-soybean harvest.  A reduction in SCN egg densities was observed in wheat strips compared to fallow strips at the R1 stage (−31.8%) and after soybean harvest (−32.7%). Field locations with noted SCN suppression were selected for a metagenomics study. The composition of fungal communities differed significantly between double-cropped and fallow plots at soybean planting and after harvest (P<0.001). A gas chromatography-mass spectrometry (GC-MS) pipeline was later implemented to investigate the profile of chemicals in the same soil samples used for the metagenomics study. Over 50 compounds were detected, including multiple fatty acids with higher concentrations in double-cropping samples compared to fallow. This multi-approach study provides a better understanding of the mechanisms in the suppression of SCN by wheat. Rather than a single mechanism, the suppression of SCN in soybean fields double-cropped with winter wheat is potentially linked to enriched microbial communities, increased populations of beneficial organisms, and higher concentrations of chemicals with nematicidal activity.