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United States Department of Agriculture

Agricultural Research Service

Related Topics

Research Project: Function of Arbuscular Mycorrhizal Fungi in Organic and Conventional Agriculture

Location: Molecular Characterization of Foodborne Pathogens

2013 Annual Report


1a.Objectives (from AD-416):
1. Overcome yield reductions due to the negative impacts on indigenous arbuscular mycorrhizal [AM] fungi of repetitive tillage and cultivation to control weeds in organic farming through inoculation with AM fungi produced via the on-farm system. 2. Optimize utilization of arbuscular mycorrhizal symbiosis to enhance crop growth and yield. 2.1) Develop greenhouse media and nutrient regimes for the production of AM fungus colonized seedlings in organic management. 2.2) Develop methods for the production of AM fungus colonized sweet corn seedlings in the greenhouse and quantify growth and yield response after outplanting. 2.3) Examine the functioning of AM fungi in high P soil in the field by determining the response to inoculation with AM fungi in field plots with greatly reduced AM fungus populations due to long term bare fallow. 3. Increase the acquisition of nitrogen by crop plants via mycorrhizal symbiosis by manipulating the regulatory processes of N uptake by arbuscular mycorrhizal fungus hyphae.


1b.Approach (from AD-416):
Arbuscular mycorrhizal [AM] fungi form a mutualistic symbiosis with the roots of the majority of crop plants. Among the benefits the plant receives are enhanced mineral nutrient uptake, drought resistance, and disease resistance. These benefits make optimal utilization of the symbiosis important to ensure the economic and environmental sustainability of US agriculture. One way to utilize the symbiosis is to inoculate vegetable seedlings with AM fungi in the greenhouse, prior to out planting in the field. This allows plants to benefit from the symbiosis immediately. We will develop inoculation strategies and greenhouse culture regimes for organic farmers to produce well colonized seedlings. Further, we will examine two farming practices that should benefit from inoculation: growth of sweet corn seedlings in the greenhouse for early transplant to the field and transplant of vegetable seedlings into soil repetitively cultivated to produce a stale weed seedbed to control weeds. Throughout, we will utilize AM fungi produced via our system for the on-farm production of inoculum. In addition, we will study the functioning of AM fungi. We will study how the nitrogen uptake and transfer to the host plant is regulated by the photosynthetic capacity of the plant. Phosphorus (P) availability is the most important regulator of development and efficacy of the symbiosis. We will conduct field experiments at the Rodale Institute to determine if plant response to the symbiosis in high P soil is affected more by the vigor of the native population of AM fungi or by intrinsic properties of the host plant which determine responsiveness. These studies will yield targeted strategies for utilization of AM fungus inoculum.


3.Progress Report:
Arbuscular mycorrhizal (AM) fungi are soil fungi which form a symbiosis with most crop plants, assisting roots in nutrient uptake and disease resistance. Better utilization of this symbiosis in agriculture through the contributions of this project should result in increased profits and sustainability, as per the Focus Area of the National Program Component. A number of field experiments were initiated for the 2013 growing season. These include examination of the impact of greenhouse nutrient regimes upon colonization of seedlings by AM fungi; continuation of our work utilizing AM fungus inoculum in tomato, pepper, and sweet potato production; and inoculation of plants grown in soils with greatly reduced AM fungus populations. In addition, an experiment was initiated to examine the impact of compost microbiological quality upon the on-farm production of AM fungus inoculum in compost and vermiculite mixtures. Metabolic studies over the past year, with collaborators at South Dakota State Univ., continue to focus on physiology and regulation of carbon and nitrogen metabolism in the symbiosis to address Objective 3: increase the acquisition of nitrogen by crop plants via the mycorrhizal symbiosis. Collaborations with other researchers at the Eastern Regional Research Center (ERRC) include studies of the impact of AM fungus colonization of roots upon the internal infection of vegetable plants by human pathogenic bacteria, the utilization of biochars to inactivate pathogenic bacteria in soil, and the use of pelleted biochar as a carrier material for AM fungus inoculum. A new project involving molecular approaches to identify AM fungus species in soil and roots was initiated. This work will facilitate studies on the functioning of AM fungus communities in organic and conventional farming systems. For example, identifying specific AM fungus species that have beneficial effects upon crop growth would allow one to target inoculum production for that crop. Experimental work has started with the extraction and analyses of DNA from single spores of AM fungi so individual species in a complex ecosystem can be identified. So far, we have identified two different AM species from DNA extracted from single spores. We have also amplified mycorrhizal fungus DNA from the bulk of plant root DNA, but to identify individual species from a mixture of fungi within a single root requires labor intensive procedures requiring additional personnel. Therefore, we seek to develop collaborations with Texas A&M University and the citrus center in Weslaco TX to engage graduate students in the project. In addition, we are trying to expand our studies to include fruit crops such as citrus and olives. Potential collaborators in the Texas olive and industries have been identified, and soil samples from organic and conventional citrus farms have been received.


4.Accomplishments
1. Fish-based organic fertilizer benefits AM fungus colonization of plant roots. Farmers may spend a significant amount of money to buy a commercially-available arbuscular mycorrhizal [AM] fungus inoculum, or effort to produce AM fungus inoculum on-farm, and mix it into potting media. This is done with the goal of producing vegetable plants colonized by AM fungi during the greenhouse growth phase. These plants would then be able to take advantage of the beneficial symbiosis (increased nutrient uptake, drought resistance, and disease resistance) immediately upon transplanting to the field. However, farmers may continue to utilize their previous greenhouse nutrient regime which can inhibit colonization of roots of the plants by the AM fungi. In particular, addition of previously-routine levels of phosphorus in fertilizer solutions will inhibit colonization of roots by AM fungi. Phosphorus is the primary nutrient supplied to the plant by the AM fungi, and if the plant can take up all the phosphorus it needs without the aid of the fungi, it does a variety of things to restrict the growth of the AM fungi. Organic farmers are particularly challenged in this respect because the ability to tailor nutrient regimes to provide all other nutrients but lower phosphorus application is limited. ARS researchers at Wyndmoor, PA, in cooperation with staff of the Rodale Institute, found that the application of a fish-based fertilizer was superior to blood meal as a nitrogen supplement with low levels of phosphorus. This result will help to ensure organic farmers produce vegetable seedlings colonized by AM fungi, ready to take advantage of the symbiosis immediately upon being transplanted to the field.

2. Setting up molecular laboratory facilities for mycorrhizae related studies. A modern well equipped facility for conducting molecular studies related to mycorrhizal fungi has been established from scratch. In addition, ARS researchers at Wyndmoor, Pennsylvania, accomplished identification of three species of AM fungi: Glomus mosseae, Glomus intraradices, and Gigaspora sp. from single spores. This will aid future studies on the impact of agricultural practices upon populations and functioning of these important fungi in organic and conventionally farmed soils.


Review Publications
Malik, N.S., Perez, J.L., Kunta, M. 2012. The effect of leaf presence on the rooting of stem cutting of bitter melon and on changes in polyamine levels. Agricultural Sciences. 3(7):936-940.

Gurtler, J., Douds, D.D., Dirks, B.A., Quinlan, J.J., Nicholson, A., Phillips, J.G., Niemira, B.A. 2013. Survival of Salmonella and E.coli O157:H7 in soil and translocation into leek (allium porrum) as influenced by mycorrhizal fungi. Applied and Environmental Microbiology. 79:1813-1820.

Malik, N.S., Perez, J.L., Kunta, M. 2013. Changes in free amino acid levels in sour orange leaves in response to cold stress and during recovery from cold stress. Journal of Food, Agriculture & Environment. 11(1):1086-1088.

Last Modified: 9/2/2014
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