Skip to main content
ARS Home » Pacific West Area » Wenatchee, Washington » Physiology and Pathology of Tree Fruits Research » Research » Research Project #441696

Research Project: Assessing Barriers to and Benefits of AMF Colonization in Apple

Location: Physiology and Pathology of Tree Fruits Research

Project Number: 2094-21220-003-004-T
Project Type: Trust Fund Cooperative Agreement

Start Date: Apr 1, 2022
End Date: Mar 31, 2025

Objective 1: Assess the ability of commercially available Arbuscular Mycorrhizal Fungi (AMF) products and pre-existing AMF communities contained in nursery-derived apple roots to compete with native AMF orchard communities. Objective 2: Assess benefits of specific apple rootstock-AMF associations including protection against root pathogenic fungi and tolerance to water stress.

Objective 1: The composition of arbuscular mycorrhizal fungal (AMF) communities pre-established (at the nursery) in apple roots will be assessed prior to planting using AMF-specific and/or fungal-specific DNA sequencing assays (AML1/AML2 and/or ITS1F/4R). Taxonomic composition (at the species level) of 5 different commercial AMF products will be verified using the AML1/AML2 primer set. Spore viability of the same set of commercial AMF products will also be tested using the 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction assay. The ability of AMF contained in select commercial products and AMF pre-established in nursery-derived apple rootstocks to compete with native AMF in orchard soils will be tested by comparing AMF community composition in apple roots after cultivation in 1) “live” orchard soils (native AMF vs. pre-existing AMF), 2) “live” orchard soils inoculated with commercial AMF (native AMF vs. both commercial and pre-existing AMF) and 3) pasteurized orchard soil control (pre-existing AMF only). Rootstocks containing nursery-derived AMF will also be cultivated in pasteurized orchard replant soils containing commercially available AMF (commercial AMF vs. pre-existing AMF). After 8-12 weeks, plants will be harvested and DNA will be extracted from new root tissue. Sequencing will be conducted using the primer sets described above. Assessment of AMF community profiles and AMF diversity in each treatment will be evaluated using Explicet software. Total AMF colonization (% colonization) will be assessed via microscopy. Objective 2: Compatible apple rootstock/AMF combinations will be pre-determined based on research which is currently being conducted in our lab. Select apple rootstocks will be inoculated with a particular AMF species and mycorrhizal colonization will be confirmed via microscopic assessment after 6-8 weeks by sacrificing a subset of plants. Next, both mycorrhizal and non-mycorrhizal plants will be exposed to the fungal replant pathogen Rhizoctonia solani via transplantation into pasteurized potting soil containing R. solani. R. solani will be cultivated in the lab and inoculated into pasteurized potting soil via hand mixing. After 8-12 weeks all plants will be harvested and previously developed qPCR assays will be used to quantify the abundance of R. solani in root tissue. The role of these apple rootstock/AMF associations in increasing plant tolerance to water stress will be tested by applying soil water deficits to potted plants with and without AMF colonization in greenhouse experiments. A variety of plant growth characteristics (e.g. root biomass, shoot biomass, trunk diameter) and physiological responses (to be determined) will be measured. All experiments will be conducted under controlled environmental conditions in the greenhouse or in growth chambers.