Development of a Standardized Soybean Cyst Nematode Screening Assay in Pennycress and Identification of Resistant Germplasm

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: (1) germination stimulants, (2) inoculation timing, (3) inoculation rate, (4) experimental incubation time, and (5) susceptible checks. The standardized SCN resistance screening protocol includes: (1) treating pennycress seeds with gibberellic acid for 24 hours, (2) transplanting seedlings 12-15 days after initiating germination and inoculating 10-12 days after transplantation, (3) inoculating at a rate of 1500 eggs/100cc soil (1500 eggs per plant), (4) processing roots at 30 days after inoculation and (5) 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, fifteen 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 US Midwest.

Pennycress domestication and improvement efforts

“…Saini et al (1987) reported increased germination of pennycress seeds using GA and potassium nitrate. Recently, Basnet, Meinhardt, et al (2023) also showed that GA could promote seed germination in wild pennycress at room temperature. As mentioned earlier, mutants with low glucosinolate tend to exhibit low germination, potentially due to lowered napin levels, a protein type correlated with increased germination (Schatzki et al, 2014).…”

“…Basnet, Meinhardt, et al. (2023), through a large germplasm screening assay, identified line Ames 32896 as consistently susceptible across two SCN Heterodera glycines type 7 and 1.2.5.7, which will be crucial to calculate FI in pennycress SCN experiments. This study further developed a pennycress SCN screening method and identified several moderately resistant pennycress lines.…”

“…More recently, in the last two decades, pennycress has been extensively studied for its potential inclusion in the corn–soybean cropping system (Hartnell et al., 2022). However, limited publicly available germplasm, with only ∼80 accessions in USDA GRIN, hinders genetic trait characterization and downstream crop breeding and improvement strategies (Basnet, Meinhardt, et al., 2023). Thus, it is crucial to collect, preserve, and increase geographically distributed genetically diverse pennycress germplasm to disseminate pennycress seed for prompting pennycress improvement and domestication efforts through the pennycress germplasm repository.…”

“…Hence, identifying a susceptible cultivar consistent across different SCN races is significant in SCN phenotyping and resistance breeding (Basnet et al, 2020). Basnet, Meinhardt, et al (2023), through a large germplasm screening assay,…”