Screening field pea (Pisum sativum L.) for tolerance to high salinity conditions
Tracy, Jacob D.
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Field pea (Pisum sativum L.) is an important salt-sensitive crop utilized in rotation with cereals in semi-arid cropping systems in the Northern Great Plains (NGP). Saline soils (EC > 4 dS m -1) negatively impact over 10.8 million acres in Montana, the second largest producer of field pea in the US. Despite its global importance, few studies have explored field pea response to high salinity conditions outside of germination testing and even fewer have looked at tolerance to sodium sulfate (Na 2SO 4), the dominant salt affecting plant growth in the NGP. In this study, 311 accessions comprising the genetically diverse USDA Pisum single plant (PSP) core collection were screened under high Na 2SO 4 conditions in germination and seedling experiments. Germination screening was conducted in petri dishes within a dark growth chamber. Accessions received H 2O (control) or 16 dS m -1 Na 2SO 4 (highly saline) solution for 8 days. The mean percent germination compared to the control was used as the indicator for tolerance. A preliminary greenhouse concentration series experiment using 7 levels of Na 2SO 4 (0, 3, 6, 9, 12, 15, and 18 dS m -1), supported screening seedlings at 9 dS m -1 Na 2SO 4. Greenhouse screening was conducted in plastic pots of coarse sand media. Accessions received a nutrient solution (control) or 9 dS m -1 Na 2SO 4 and nutrient solution daily. Salinity symptom scores were assessed on days 21, 28, 35, and 38 post-sowing using a visual growth response scale of 1-9 (healthy-dead). Phenotypic measurements and the Area Under the Injury Curve (AUIC) were used as indicators for tolerance. A Genome Wide Association Study (GWAS) was conducted using the phenotypic data collected and a large dataset of 68,222 Single Nucleotide Polymorphisms developed from the USDA PSP plus core collection. Potential candidate breeding germplasm conferring high salinity tolerance at the germination and seedling growth stages was identified. Significant marker-trait associations were discovered for all traits measured, providing potential Marker-Assisted Selection (MAS) opportunities.