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Title:   Author  item
                                            Samac, Deborah

                                                         - *Debby*item
                                            KINKEL, LINDA - UNIVERSITY OF MINNESOTA
  Submitted to: Plant and Soil
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 6/8/2001
                                    Publication  Date: 8/1/2001
                                    Citation: Samac, D.A., Kinkel, L.L. 2001. Suppression of the root-lesion nematode (Pratylenchus penetrans) in alfalfa (Medicago sativa) by Streptomyces spp. Plant and Soil. 235:35-44.Interpretive Summary: Streptomycetes are filamentous bacteria that secrete a wide array of antibiotics and hydrolytic enzymes. A number of species have been shown to produce compounds that inhibit the growth of plant-pathogenic fungi and bacteria. Many Streptomycetes grow on plant roots and protect roots from pathogens making them attractive biological control agents against soil-  borne plant pathogens. As nematicides are removed from the market, there i an increasing need for methods to control damage to plants from feeding by nematodes. We tested antibiotic-producing strains of Streptomyces for their ability to reduce population densities of the root-lesion nematode (RLN) in alfalfa roots. Inoculation of soil with Streptomyces at planting significantly reduced RLN population densities in roots of both susceptible and resistant varieties grown in either pasteurized or unpasteurized soil. Reductions in RLN population densities were observed 6 weeks after nematode einoculation. Shoot dry matter was not affected by any treatment. However, root dry weight was reduced in Streptomyces plus nematode treatments compared to the nematode inoculation alone in some experiments. Root weights were not affected by Streptomyces when RLN was absent. Mutant strains that do not produce antibiotics in culture also reduced RLN population densities in alfalfa roots. All strains maintained high population densities in pasteurized soil and on alfalfa roots. Although their persistence and effectiveness in field soil need to be tested, these strains may be useful in managing a range of diseases in multiple crops. Development of such biological controls will give growers more choices for controlling diseases economically.
                                Technical Abstract: Strains of Streptomyces were tested for their ability to reduce population densities of the root lesion nematode (RLN), Pratylenchus penetrans, in roots of alfalfa (Medicago sativa) in growth chamber assays. Previously, these strains were shown to suppress potato scab disease caused by Streptomyces scabies in field experiments and to inhibit in vitro growth of fa wide range of plant-pathogenic fungi and bacteria. Inoculation with Streptomyces at planting significantly reduced RLN population densities in roots of both susceptible and resistant varieties grown in either pasteurized or unpasteurized soil. Reductions in RLN population densities were observed 6 weeks after nematode inoculation. Shoot dry matter was not affected by any treatment; root dry weight was reduced in Streptomyces plus nematode treatments compared to the nematode inoculation alone in some experiments but not affected by Streptomyces when RLN was absent. Mutant  strains not producing antibiotics in vitro also reduced RLN population densities in alfalfa roots, and all strains maintained high population densities in pasteurized soil and on alfalfa roots. These strains may be useful in multi-crop, multi-pathogen management programs to augment genetic resistance of plant diseases.


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