Location: Physiology and Pathology of Tree Fruits Research
Project Number: 2094-21220-003-008-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Jan 17, 2023
End Date: Jan 31, 2025
Objective:
1. Characterize the capacity 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.
2. Identify benefits of specific apple rootstock-AMF associations including protection against root pathogenic fungi and tolerance to water stress.
Approach:
Objective 1: Arbuscular mycorrhizal fungi (AMF) are root-colonizing endophytes present in most terrestrial ecosystems, including agricultural soils. This research will evaluate the ability of a variety of commercially available AMF products designed for soil application to successfully compete with native orchard AMF communities as well as pre-established AMF communities contained in nursery-derived apple rootstocks. Highly infective (at least 30-40% mycorrhizal establishment in apple seedlings) AMF inocula will be selected for use in experiments designed to assess the ability of commercially available AMF to compete with native AMF and other indigenous fungi in “live” orchard soil. Taxonomic composition of the endophytic fungal communities in rootstocks cultivated in “live” orchard soil will be compared with those in “live” orchard soil + commercial inoculum. The influence of nursery-derived AMF (pre-existing in root tissue) on AMF community structure will also be explored by comparing these results with AMF communities in root samples collected prior to planting. Identifying whether native AMF and/or pre-established AMF communities limit effective colonization by mycorrhizal inoculants will be an integral step towards developing strategies for more effective use of these products and/or for manipulating native AMF composition and diversity in the field.
Objective 2: AMF have been shown to provide a spectrum of benefits to their plant hosts including improved tolerance to water stress, improved access to nutrients and disease resistance. However, these functional benefits may be fungus- and plant-species dependent. This research will assess the ability of specific apple rootstock/AMF associations to control soil-borne fungal pathogens involved in apple replant disease. Compatible rootstock/AMF combinations will be selected based on data from research previously conducted in the ARS lab. The ability of the specific rootstock/AMF associations to enhance plant defense against subsequent pathogen infection will be tested by challenging mycorrhizal and non-mycorrhizal tissue-cultured plantlets with the fungal replant pathogen Rhizoctonia solani AG-5. Upon harvest, the amount of R. solani DNA per gram of root tissue will be quantified using a previously developed real-time quantitative polymerase chain reaction (qPCR) assay. It has also been shown that water transport by mycorrhizal fungi may improve plant access to available soil water under drying conditions. The effects of a commercially prepared R. irregularis AMF inoculum on rootstock tolerance to short-term water stress in “live” orchard replant soil will also be explored. Under water-stressed conditions, plants cultivated in “live” orchard soil + R. irregularis are expected to be less affected than those grown in “live” orchard soil only. These experiments are expected to provide clear evidence of AMF species directly functioning in beneficial roles with commercially available apple rootstock genotypes, and will provide insight into specific AMF-rootstock relationships which could be harnessed to improve disease control, drought tolerance and sustainability.
