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ARS Home » Midwest Area » St. Paul, Minnesota » Plant Science Research » Research » Publications at this Location » Publication #69205


item Samac, Deborah - Debby

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 7/14/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Successful control of Phytophthora root rot (Phytophthora medicaginis) on alfalfa (Medicago sativa) by a disease suppressive Streptomyces isolate has been previously demonstrated in greenhouse experiments, although tests in field settings have proven less successful. Information regarding the molecular and biochemical mechanisms of disease suppression in this system have not been investigated. We have set out to investigate the effect of the biological control agent on a number of isolates of P. megasperma and on gene expression in resistant and susceptible cultivars of alfalfa (by analyzing mRNA levels of known defense response genes). We also have begun to investigate the potential of the biological control agent to suppress a serious foliar pathogen of alfalfa, Phoma medicaginis. Sensitivity of several Phytophthora and Phoma isolates to antibiotics produced by Streptomyces isolate 93, a previously identified candidate for biocontrol, was tested by overlaying a suspension of each fungus over colonies of Streptomyces. Phoma isolates were not inhibited in any trials with Streptomyces isolate 93 over a 7-day period. This indicates that foliar application of isolate 93 may not control Phoma. Variability in inhibition was exhibited by nine Phytophthora isolates in a range from 19.5 to 23.1 mm diameter from Streptomyces colonies. These isolates will be tested in greenhouse assays with alfalfa seedlings to determine if strains more sensitive to antibiosis show better disease control by Streptomyces. A number of plant growth promoting rhizobacteria have been shown to induce systemic disease resistance in plants. We are testing the systemic effect of Streptomyces application to alfalfa plats by analyzing mRNA levels of known defense response genes.