Influence of microbial species and functional diversity in soils on pathogen dispersal and ecosystem processes in organic and conventional agroecosystems

Project Overview

Project Type: Research and Education
Funds awarded in 2001: $167,842.00
Projected End Date: 12/31/2003
Region: Southern
State: North Carolina
Principal Investigator:
Jean Ristaino
North Carolina State University

Annual Reports


  • Agronomic: rye
  • Fruits: berries (strawberries)
  • Vegetables: sweet potatoes, cucurbits, greens (leafy), peppers, tomatoes
  • Additional Plants: herbs


  • Crop Production: conservation tillage
  • Education and Training: demonstration, extension, on-farm/ranch research, participatory research
  • Farm Business Management: budgets/cost and returns
  • Natural Resources/Environment: biodiversity, habitat enhancement, soil stabilization
  • Pest Management: biological control, biorational pesticides, botanical pesticides, cultural control, field monitoring/scouting, integrated pest management, mulches - killed, soil solarization
  • Production Systems: agroecosystems, holistic management
  • Soil Management: green manures, organic matter, soil analysis, composting, soil quality/health
  • Sustainable Communities: partnerships, sustainability measures


    The objectives of our research were to examine the influence of microbial species and functional diversity and composition on the invasion of soils from conventional and organic agroecosystems by the Basidiomycete plant pathogen Sclerotium rolfsii, causal agent of Southern blight. Specifically, we contrasted conventional soil fertility amendments including synthetic fertilizers, and organic soil fertility amendments, including either composted plant materials, animal manures, or incorporated green manures on the spread of S. rolfsii and the community dynamics of selected microflora in field plots. We evaluated the resistance of conventional, sustainable and organic agrecosystem soils to species invasion and colonization by S. rolfsii. Soils amended with organic amendments such as cotton gin trash were more suppressive to southern blight than soils from plots amended with synthetic fertilizers. These soils were colonized less rapidly over time by the pathogen and disease incidence was reduced and yield was higher at harvest. Soils with organic amendments had higher populations of thermophilic organisms. Grower field soils from conventional, organic and sustainable farms were sampled and assayed for disease suppressiveness in greenhouse assays. Soils from organic farms were more suppressive to disease than soils from sustainable or conventional farms in each season. These soils contained bacterial communities that were more diverse than soils from conventional farms. Soils from organic farms had higher levels of extractable C and N, higher microbial biomass carbon and nitrogen, and net mineralizable N. In addition, soil microbial respiration was higher in soils from organic than sustainable or conventional farms, indicating that microbial activity was greater in these soils. We are currently examining the functional and species components of soil microbial communities associated with disease suppressiveness.

    Project objectives:

    In this research we addressed the following objectives:

    Objective 1. Are soils from organic agroecosystems more resistant than soils from conventional agroecosystems to invasion by the soilborne plant pathogen S. rolfsii? How do the spatial patterns of disease symptom expression relate to pathogen propagules of S. rolfsii in soils in field plots from conventional and organic agroecosystems?

    Objective 2. Are grower field soils from organic farms amended with organic fertility amendments more suppressive to disease caused by S. rolfsii than soils from conventional farms amended with synthetic fertility amendments? Is species diversity, functional diversity or the composition of the soil microflora most closely related to disease suppressiveness?

    Objective 3. Continue education and outreach plans by teaching graduate level courses relevant to sustainable agriculture research, conducting on-farm research and education, and presenting data at conferences with a focus on ecology in agriculture.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.