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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Molecular Plant Pathology Laboratory » Research » Research Project #424531

Research Project: Regulation of Gene Expression in Alfalfa Development and Stress Tolerance

Location: Molecular Plant Pathology Laboratory

2017 Annual Report


Objectives
1. Improve the efficiency of developing alfalfa with greater tolerance to biotic and abiotic stresses by characterizing gene-stress responses and pathways. Biotic and abiotic stresses cause significant yield losses in alfalfa and greatly reduce the crop’s productivity. Understanding the molecular mechanisms of stress tolerance and the ways by which stress-responsive genes are regulated is essential for improvement of alfalfa adaptability and breeding programs. 2. Aid plant breeders in improving alfalfa productivity and adaptability by implementing genetic and genomic approaches to improve traits related to biotic and abiotic stress tolerance, including, but not limited to, root-knot nematodes and salinity tolerance. Data on stress-responsive genes obtained in this study and other information on alfalfa genomics will be used to identify molecular markers associated with resistance and adaptation to abiotic and biotic stresses in alfalfa.


Approach
The research project will identify stress-responsive gene-candidates in alfalfa and assign them to cognate functional groups related to specific stress responses. It will quantify and confirm roles of the selected genes in adaptation to abiotic and biotic stresses and in regulation of stress responses. Sequence polymorphism in genes underlying stress tolerance will be delineated and molecular markers associated with resistance and adaptation of alfalfa to biotic and abiotic stresses developed. Markers will be validated through cooperative research collaborations.


Progress Report
A large-scale genome-wide association study (GWAS) is in progress to develop molecular markers associated with salinity tolerance in alfalfa. Transcriptome analysis of alfalfa plants resistant and susceptible to bacterial stem blight is in the final stages. Characterization of a novel marafivirus infecting alfalfa in France has been initiated.


Accomplishments
1. Identification and characterization of a new plant virus species infecting alfalfa. In collaboration with ARS scientists from National Germplasm Recourses Laboratory, Beltsville Maryland, we have discovered a new virus species infecting alfalfa. The virus was provisionally named alfalfa virus S (AVS). AVS was found in alfalfa samples originating from Sudan, Northern Africa. We determined a complete nucleotide sequence and genome structure of the virus and developed sensitive methods for accurate diagnostics of AVS. These methods can be used for identification and control of the virus in single infection or in complex multiviral epidemics of alfalfa.

2. Identification and characterization of a new strain of plant virus infecting alfalfa. Recently, a new virus associated with a major alfalfa dwarfism disease that threatens alfalfa production has been discovered in Argentina. In collaboration with ARS scientists from National Germplasm Recourses Laboratory, Beltsville Maryland, we identified a new strain of this virus in alfalfa samples originating from Sudan. The virus was tentatively named alfalfa enamovirus 2 (AEV-2). We determined a complete nucleotide sequence and genome structure of the virus and developed sensitive molecular tools for accurate diagnostics of AEV-2. The first incidence of the virus in a different location (Sudan) suggests that it might be widespread and possibly occurs in other alfalfa cultivation regions worldwide, including the U.S. Genome sequence and molecular diagnostics methods developed in this research can be used for identification and control of this emerging pathogen.

3. Uncovering molecular mechanisms involved in alfalfa resistance to bacterial stem blight. Bacterial stem blight of alfalfa caused by Pseudomonas syringae pv. syringae is common in the central and western U.S. and the disease occasionally occurs in eastern states. There are no cultivars selected for resistance to this disease and no known chemical control; also, little is known about host-pathogen interactions; the means of bacterial pathogenicity in alfalfa, determinants of virulence, host defense mechanisms, and sources of resistance are absent in the literature. Therefore, there is an urgent need to address these issues and respond to the threat represented by this emerging pathogen in order to lessen the impact on alfalfa producers and farm incomes. In collaboration with ARS scientists in Saint Paul, Minnesota, we addressed these gaps by identifying molecular mechanisms of alfalfa resistance to bacterial stem blight. Key genes and processes involved in bacterial pathogenicity and host resistance were determined. These data will be in valuable for developing cultivars with high levels of resistance to the disease.


Review Publications
Nemchinov, L.G., Grinstead, S.C., Mollov, D.S. 2017. Alfalfa virus S, a new species in the family Alhapflexiviridae. PLoS One. 12(5):e0178222.
Nemchinov, L.G. 2017. Development and characterization of the first infectious clone of alfalfa latent virus, a strain of Pea streak virus. European Journal of Plant Pathology. doi:10.1007/s10658-017-1237-2.
Nemchinov, L.G., Grinstead, S.C., Mollov, D.S. 2017. A first report and complete genome sequence of alfalfa enamovirus from Sudan. Genome Announcements. e00531-17. doi: 10.1128/genomeA.00531-17.