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ARS Home » Midwest Area » St. Paul, Minnesota » Plant Science Research » Research » Publications at this Location » Publication #311772
Title: Seed treatments: New tools for combating seedling diseases of alfalfa in organic and conventional production systems

Author
item Samac, Deborah - Debby
item BLOSBERG, JESSICA - Former ARS Employee
item SATHOFF, ANDREW - University Of Minnesota
item KINKEL, LINDA - University Of Minnesota

Submitted to: Forage Focus
Publication Type: Trade Journal
Publication Acceptance Date: 10/24/2015
Publication Date: 12/1/2014
Citation: Samac, D.A., Blosberg, J., Sathoff, A., Kinkel, L.L. 2014. Seed treatments: New tools for combating seedling diseases of alfalfa in organic and conventional production systems. Forage Focus. December 2014 Pages 8-9.

Interpretive Summary:

Technical Abstract: Alfalfa seeds and seedlings are vulnerable to pathogens in the soil that reduce stand density and damage root systems. For alfalfa, strong seedling establishment is particularly important to achieve the plant density needed to out-compete weeds and produce high biomass yields. The majority of alfalfa seed is treated commercially with the systemic fungicide mefenoxam, Apron XL. This provides protection against Pythium seed rot and damping-off and boosts resistance to Phytophthora root rot (PRR). However, Apron XL does not provide protection against Aphanomyces root rot (ARR). Although most modern alfalfa cultivars have resistance to race 1 of A. euteiches, fewer have been developed with resistance to both race 1 and race 2. Research in the ARS Plant Science Research Unit in St. Paul, MN has investigated several new seed treatments for protecting alfalfa seeds. A mineral seed coating using aluminosilicate (natural zeolite) on alfalfa seed was found to have strong activity against PRR, ARR and Pythium damping off. The coated seeds were also grown in soils from commercial alfalfa production fields with different levels of pathogens infecting alfalfa seeds and seedlings. The zeolite coating was as effective or more effective than the Apron XL treatment in the majority of soil samples. Recently, the fungicide Stamina was labeled for use on alfalfa seed. The active ingredient was tested in an agar plate assay to determine the amount needed to inhibit growth of Aphanomyces strains by 50% (EC50). Both race 1 and race 2 strains were very sensitive to the fungicide with an EC50 ranging from 5-49 ppm depending on the strain and overall average EC50 for the six strains tested of 22 ppm. Seed of a race 2-susceptible cultivar were treated with Stamina at the labeled rate, grown for 7 days in a growth chamber and then inoculated with race 2 strains of Aphanomyces. At 2 weeks after inoculation, the Stamina treatment resulted in 47% healthy seedlings while all of the control and Apron XL-treated seed were diseased. However, in tests with Pythium, the Stamina treatment resulted in an average of 15% healthy seedlings, the Apron treatment with 55% healthy seedlings, and the control with 0% healthy seedlings. Microbial seed treatments have received attention for promoting growth and reducing disease in other crops. However, few microbials have been tested for use with alfalfa. Streptomycete isolates were tested for their ability to control PRR in naturally infested field soil. Several strains significantly reduced disease symptoms and increased plant biomass in the absence of the pathogen. These result suggest that novel seed treatments can be useful in controlling seedling diseases of alfalfa in organic and conventional alfalfa production systems.