Location: Plant Science ResearchTitle: Microbial communities in the cysts of soybean cyst nematode affected by tillage and biocide in a suppressive soil Author
|Samac, Deborah - Debby|
Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2017
Publication Date: 7/31/2017
Citation: Hu, W., Samac, D.A., Liu, X., Chen, S. 2017. Microbial communities in the cysts of soybean cyst nematode affected by tillage and biocide in a suppressive soil. Applied Soil Ecology. 119(2017):396-406. Interpretive Summary: The soybean cyst nematode (SCN) is one of the most important pests of soybean worldwide. Limited sources of genetic resistance in soybean, rapid changes in virulence in SCN populations, and restrictions in chemical control methods make management of this pest difficult. When soybean is grown continuously for long periods of time, the soil becomes suppressive to the nematode, significantly reducing nematode populations. This study investigated the bacterial and fungal populations associated with cysts in suppressive soil and soil treated with a biocide to reduce suppressiveness. We found that suppressiveness was stable in soils under conventional tillage and no-tillage treatments. The biocide reduced suppressiveness and altered the microbial populations. Several fungi and bacterial species were associated with cysts in control treatments and were reduced by the biocide. These studies indicate that both bacteria and fungi play important roles in colonizing cysts and suppressing SCN populations. Identifying these microbes is an important step for understanding the mechanisms of nematode-suppressive soil and developing effective biocontrol agents or management strategies to reduce SCN populations. Effective control of SCN will provide significant economic returns for soybean producers and reduce reliance on chemical controls that are harmful to the environment.
Technical Abstract: Suppressive soil harbors biological agents with potential for controlling plant diseases. However, given the rich and complex composition of suppressive factors, the bacteria and fungi involved in disease suppression have been difficult to identify. We conducted amplicon-based metagenomic analysis of microbial communities in the cysts of soybean cyst nematode (SCN, Heterodera glycines) from an SCN-suppressive field to study bacteria and fungi involved in the SCN suppression. The experiment was a split-plot design with conventional tillage and no-till as main treatments, and formaldehyde as a biocide and no-formaldehyde (control) as sub-treatments. All plots were planted to SCN-susceptible soybean during the study from 2009-2013. Tillage had little effect on SCN, while formaldehyde increased SCN population density, suggesting biological factors involved in SCN suppression. SCN cysts were collected at planting and midseason in 2013 for bacterial 16S rRNA and fungal ITS1 sequencing. Tillage did not affect bacterial and fungal diversity, composition, or relative abundance of taxa. However, formaldehyde lowered bacterial community diversity, and changed the bacterial and fungal community composition when compared to the control. Formaldehyde reduced the bacteria Lysobacter and Actinocorallia, which are frequently isolated from cysts, but increased relative abundance of Pseudomonas in the cysts. Streptomyces was more dominant at planting than midseason. The fungi important in regulating SCN population such as Pochonia, Exophiala, and Clonostachys had lower relative abundance, whereas Trichoderma and Phoma had higher relative abundance under formaldehyde treatment than control. Our study suggests that both bacteria and fungi played important roles in suppression of SCN.