Genetic mapping of tolerance to bacterial stem blight caused by Pseudomonas syringae pv. syringae in alfalfa (Medicago sativa L.)

Authors: MOYA, YEIDYMAR - University Of Minnesota; MEDINA, CESAR - University Of Minnesota; HERRERA, BIANCA - University Of Minnesota; CHAMBA, FABIAN - University Of Minnesota; Yu, Long-Xi; Xu, Zhanyou; Samac, Deborah - Debby

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/25/2023
Publication Date: 12/29/2023
Citation: Moya, Y.S., Medina, C., Herrera, B., Chamba, F., Yu, L., Xu, Z., Samac, D.A. 2023. Genetic mapping of tolerance to bacterial stem blight caused by Pseudomonas syringae pv. syringae in alfalfa (Medicago sativa L.). Plants. 12(1). Article 110. https://doi.org/10.3390/plants13010110.
DOI: https://doi.org/10.3390/plants13010110

Interpretive Summary: Foliar diseases of alfalfa reduce yield and nutritional content of harvested forage. Bacterial stem blight of alfalfa can reduce the first forage harvest by 50%. This disease has recently been observed causing significant yield losses in the western United States. There are currently no methods for controlling this disease. Screening of diverse alfalfa germplasm identified disease resistant plants in the cultivar ZG9830 and a population was developed for mapping the genes for resistance to bacterial stem blight. After inoculation with the bacterium, the plants without disease symptoms had bacterial populations like plants with severe disease symptoms indicating tolerance to the disease. Potential genes involved in tolerance were identified. These genes and DNA markers within the genes can be used by plant breeders to develop cultivars with tolerance to bacterial stem blight and increase forage yields in areas where the disease occurs.

Technical Abstract: Bacterial stem blight of alfalfa (Medicago sativa L.), first reported in the United States in 1904, has emerged recently as a serious disease problem in the western states. The causal agent, Pseudomo-nas syringae pv. syringae, promotes frost damage and disease that can reduce first harvest yields by 50%. Resistant cultivars and an understanding of host-pathogen interactions are lacking in this pathosystem. With the goal of identifying DNA markers associated with disease resistance, we developed biparental F1 mapping populations using plants from the cultivar ZG9830. Leaflets of plants in the mapping populations were inoculated with a bacterial suspension using a needle-less syringe and scored for disease symptoms. Bacterial populations were measured by culture plating and using a quantitative PCR assay. Surprisingly, leaflets with few to no symptoms had bacterial loads similar to leaflets with severe disease symptoms, indicating that plants without symptoms were tolerant of the bacterium. Genotyping-by-sequencing was used to identify 11 sig-nificant SNP markers associated with the tolerance phenotype. This is the first study to identify DNA markers associated with tolerance to P. syringae. These results provide insight into host re-sponses and the development of cultivars to manage bacterial stem blight of alfalfa.