Location: Sustainable Biofuels and Co-products Research
2023 Annual Report
Objectives
Objective 1: Determine the impact of management practices on AMF community dynamics and AMF colonization efficiency of crops, and the resulting impact on crop yield and quality.
Sub-objective 1.A: Determine optimal AMF inoculum composition for production of sweet corn and winter squash under organic and conventional management practices.
Sub-objective 1.B: Identify the impact of soil microbial dynamics caused by farm management practices on outcomes of AMF inoculations.
Objective 2: Determine the physiological and transcriptional responses of AMF to phytochemical signals and environmental conditions promoting spore germination and growth.
Sub-objective 2.A: Evaluate whether abietic acid and dehydroabietic acid are signals that activate carbon uptake by AM fungi.
Sub-objective 2.B: Evaluate whether hypoxia is a physiologic condition that activates carbon uptake by AM fungi, either acting alone or in combination with signals derived from root exudates.
Approach
For Obj. 1A, a greenhouse trial will be conducted to evaluate the infectivity
potential of nine different AMF species on sweet corn and winter squash seedlings. Seedlings will be harvested at 10 and 30 days after germination for analysis of root colonization and biomass measurements. Colonization will be measured by root staining/microscopy and molecular methods. Biomass measurements and mineral nutrient content will be analyzed.
For Obj. 1B, the three top-performing AMF isolates from 1A will be selected for
field trials. Field trials will be conducted within the Rodale Institute’s Vegetable Systems Trial (VST). Tillage systems consist of two organic and two conventional systems, and within each pair one utilizes plastic mulch for weed suppression and the other utilizes a cover crop. Mycorrhizal yield response will be evaluated. The field trial will be repeated a second year, and the results will be used to design a larger field study.
For Obj. 2A, spores of R. irregularis will be used in immobilized cell cultre in
phytagel M medium with 13C labelled glucose, AA, DHA,and Myr-K media amendments.
Growth and sporulation will be monitored. Lipid uptake will be assessed by
fluorescence microscopy, and uptake of carbohydrates will be measured by NMR. Based on biomass yield and uptake/labeling of 13C, an RNA-Seq experiment will be designed to capture genes differentially expressed in response to the amendments.
For Obj. 2B, spore germination and hyphal growth responses of two AMF species,
Gigaspora gigantea and R. irregularis, will be evaluated in response to partially
purified root exudates and reduced oxygen conditions (hypoxia). Carbohydrate and
lipid uptake will be measured by NMR and fluorescence microscopy as in 2A.
Progress Report
For Objective 1.B, a second year replication of Arbuscular Mycorrhizal Fungi (AMF) inoculation sweet corn and butternut squash field trials were conducted within the Rodale Institute’s Vegetable Systems Trial. Funding to Rodale for this project was awarded through a Pennsylvania Department of Agriculture Specialty Crop Block Grant with ARS as a collaborator, “Impact of Management Practices on Soil Mycorrhizal Fungi and Nutrient Uptake in Vegetable Crops,” ARIS Log No. 66605. Analysis of vitamin B6 concentration in butternut squash from this trial showed an increase of approximately 15% in fruit of plants which were inoculated with Rhizophagus irregularis or Funneliformis mosseae, compared to controls. Additional nutritional analysis is pending and data is being compiled as it becomes available.
For Objective 2.A and Objective 2.B, experiments are ongoing and milestones are anticipated to be met within the 24-month period ending November, 2023. Spore germination methodology is being refined and nuclear magnetic resonance (NMR) and RNA-Seq experiments are being designed to identify fungal responses to particular chemical signals and the physiological condition of hypoxia.
Accomplishments
1. Enhanced nutritional quality of crops through fungal inoculation. ARS researchers in Wyndmoor, Pennsylvania, used controlled inoculation trials to identify favorable Arbuscular Mycorrhizal Fungi (AMF) biofertilizer compositions to improve crop yield and crop nutritional content. AMF are naturally occurring soil fungi which form symbiotic associations with plant roots and enhance plant mineral nutrient uptake, but their development as agricultural products has been limited by their complex genetics and technological challenges to their cultivation. In addition to enhancing mineral nutrient content, inoculation trials of potatoes, beans, asparagus, wheat, and oats confirmed a previously untested hypothesis that AMF are involved in plant bioaccumulation of the antioxidant ergothioneine, an amino acid synthesized only by fungi and certain bacteria which has recently gained significant attention as a vitamin which prevents neurodegenerative disorders and cardiovascular disease in humans. Supplemental inoculation of native soil with AMF spores doubled the ergothioneine content of wheat and oats, widely consumed cereal grains whose nutritional fortification has far-reaching public health benefits. Inoculation of another staple crop, potatoes, resulted in a nine-fold increase in tuber ergothioneine content and more than a two-fold increase in antioxidant activity overall. Collectively, this research aids the development of crop-specific formulations of AMF biofertilizers which will enhance agricultural sustainability and improve crop yield and food nutritional quality for all consumers.
Review Publications
Carrara, J.E., Heller, W. 2023. Impact of AMF inoculation on nutrient uptake and growth of sweet corn (Zea mays) and butternut squash (Cucurbita moschata) seedlings. Frontiers in Agronomy. 4:1040054. https://doi.org/10.3389/fagro.2022.1040054.
Carrara, J.E., Reddivar, L., Lehotay, S.J., Zanati, G., Heller, W. 2023. Arbuscular mycorrhizal inoculation increases yield and nutritional quality of yellow and purple fleshed potatoes (Solanum tuberosum). American Journal of Potato Research. 100:210-220. https://doi.org/10.1007/s12230-023-09910-w.
Carrara, J.E., Lehotay, S.J., Lightfield, A.R., Sun, D., Richie Jr., J.P., Smith, A.H., Heller, W. 2023. Linking soil health to human health: Arbuscular mycorrhizae play a key role in plant uptake of the antioxidant ergothioneine from soils. Plants, People, Planet. 5:449-458. https://doi.org/10.1002/ppp3.10365.
