Impaired nodule function in Medicago polymorpha L. infected with alfalfa mosaic virus

Area of Science:

• Plant Pathology
• Agricultural Science
• Virology

Background:

• Annual burr medic (Medicago polymorpha) is a vital legume for agriculture.
• Alfalfa mosaic virus (AMV) is a significant plant pathogen affecting various crops.

Purpose of the Study:

• To investigate the impact of AMV on the growth, nodulation, and nodule function of Medicago polymorpha.
• To determine if AMV affects nitrogen fixation efficiency in annual burr medic.

Main Methods:

• Glasshouse pot experiments were conducted using AMV-infected and healthy Medicago polymorpha cv. Circle Valley.
• Plant growth parameters, nodule formation, nodule mass, and nitrogen fixation were measured at 53 and 75 days post-germination.
• ELISAs were used to detect AMV antigen in nodules.

Main Results:

• AMV-infected plants exhibited reduced shoot dry weight (21-22%) and fixed nitrogen accumulation (15-24%) compared to healthy plants.
• Nodule function was impaired, with decreased nitrogenase specific activity (25%) and soluble amino acids (20%) at 53 days.
• While nodule number was unaffected, nodule mass decreased by 23% at 53 days but recovered by 75 days. Nodules were active sites of AMV multiplication.

Conclusions:

• AMV infection negatively impacts Medicago polymorpha growth primarily through impaired nodule function and nitrogen fixation, not nodulation itself.
• Virus multiplication within nodules suggests a direct detrimental effect on symbiotic nitrogen fixation.
• Plants may exhibit some compensatory mechanisms, as indicated by increased nodule mass relative to plant weight later in development.