Development of a standardized soybean cyst nematode screening assay in pennycress and identification of resistant germplasm

Authors: BASNET, PAWAN - University Of Missouri; MEINHARDT, CLINTON - University Of Missouri; DHITAL, BISHNU - University Of Missouri; NGUYEN, ALICE - University Of Missouri; Gillman, Jason; JOSHI, TRUPTI - University Of Missouri; MITCHUM, MELISSA - University Of Georgia; SCABOO, ANDREW - University Of Missouri

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2023
Publication Date: 2/10/2024
Citation: Basnet, P., Meinhardt, C.G., Dhital, B., Nguyen, A., Gillman, J.D., Joshi, T., Mitchum, M.G., Scaboo, A. 2024. Development of a standardized soybean cyst nematode screening assay in pennycress and identification of resistant germplasm. Plant Disease. 108(2):359-364. https://doi.org/10.1094/PDIS-05-23-0858-RE.
DOI: https://doi.org/10.1094/PDIS-05-23-0858-RE

Interpretive Summary: A corn/soybean annual crop rotation is commonly used in the United States to reduce the accumulation of corn and soybean specific pests and pathogens. While beneficial, this rotation still leaves the winter months with bare soil. One proposed solution has been the use of cover crops which has been shown to decrease soil erosion, mitigate the loss of fertilizer nutrients due to reduced leaching and improve soil health. Pennycress (Thlaspi arvense L.) is a promising winter annual oilseed cover crop which has strong potential to increase farm profitability if included as a cover crop in the soybean/corn rotation. However, pennycress is vulnerable to infestation by the major yield-costing pest Soybean Cyst Nematode (SCN). In order to identify pennycress accessions which have resistance to SCN, we developed a standardized screening procedure and utilized this new procedure to screen 95 pennycress accessions. We identified 12 accessions which were resistant to SCN infestation. These results will not only enable more accurate screening for SCN resistance as well as improving ongoing efforts to domesticate/breed improved pennycress varieties for use as cover crops.

Technical Abstract: The prospect of incorporating pennycress as an oilseed cover crop in the Midwest’s corn-soybean rotation system has drawn researcher and farmer attention. The inclusion of pennycress will be beneficial as it provides an excellent soil cover to reduce soil erosion and nutrient leaching while serving as an additional source for oilseed production and income. However, pennycress is an alternative host for soybean cyst nematode (SCN), which is a major biological threat to soybean that needs to be addressed for sustainable pennycress adoption into our current production systems. To develop a standardized SCN resistance screening strategy in pennycress, we tested and optimized five parameters: (i) germination stimulants, (ii) inoculation timing, (iii) inoculation rate, (iv) experimental incubation time, and (v) susceptible checks. The standardized SCN resistance screening protocol includes the following: (i) treating pennycress seeds with gibberellic acid for 24 h, (ii) transplanting seedlings 12 to 15 days after initiating germination and inoculating 10 to 12 days after transplantation, (iii) inoculating at a rate of 1,500 eggs/100 cc soil (1,500 eggs per plant), (iv) processing roots at 30 days after inoculation, and (v) using susceptible pennycress accession Ames 32869 to calculate the female index. The standardized protocol was used to quantify the response of a diverse set of pennycress accessions for response against SCN HG type 1.2.5.7 and HG type 7. While there were no highly resistant pennycress lines identified, 15 were rated as moderately resistant to HG type 1.2.5.7, and eight were rated moderately resistant to HG type 7. The resistant lines identified in this study could be utilized to develop SCN-resistant pennycress cultivars. The study also opens a new avenue for research to understand SCN-pennycress interactions through molecular and genomic studies. This knowledge could aid in the successful inclusion of pennycress as a beneficial cover/oilseed crop in the United States Midwest.