1a. Objectives (from AD-416):
1) Determine if there is value in adding arbuscular mycorrhizal (AM) fungi inoculum, particularly at planting. 2) Determine if pre-plant fumigation impacts the extent and nature of AM fungal populations in the soil and is this of consequence? 3) Characterize the AM fungi populations present on field grown nursery stock vs. potted plants at the time of planting and the resulting tree performance.
1b. Approach (from AD-416):
Nonpareil almond trees on Nemaguard rootstock will be planted in Spring 2008 at USDA Parlier. Plot strips will be fumigated in the fall of 2007 and non-fumigated plot strips will be used as comparison. An assessment of the extent and nature of AM fungi populations present in the soil/residual roots after fumigation but before planting. At time of planting and before any inoculation, there will be an assessment of the extent and nature of AM present on tree roots. Tree performance data to be collected will include: (1 Trunk circumference: initial and final yearly. (2 Annual pruning weights; Nutrient status-characterize nutritional deficiencies if and when symptoms arise. 3. At end of trial: Whole tree top weight, trunk diameter, etc. Annual assessments will be made of the extent and nature of AM fungal populations on tree roots.
3. Progress Report:
Soil borne arbuscular mycorrhizal (AM) fungus forms a symbiotic (mutuality) relationship with most plants. The fungus colonizes the root and grows out into the soil. The hyphae net work, the part of the fungus that is in the soil, acts as an extension of the root system. The AM symbiosis improves plant phosphorus, nitrogen and mineral nutrition. Evidence also suggests the symbiosis provides protection of the plant against pathogens and improves plant water relations. In addition to facilitating nutrient uptake, some mycorrhizae secrete a gluey substance called glomalin which helps develop soil structure and soil aggregation favorable for plant growth. The beneficial effect of AMF on plant water stress should be investigated in almond production. The status of AM fungal population in almond orchards is not well understood. The purpose of this study is to determine if specific agronomic practices, such as pre-plant fumigation and inoculation with AM fungus, have an impact on AM fungal populations and subsequent tree performance. Almond trees planted for this project are now in their fourth year of growth in fumigated and non-fumigated soils. Root and soil samples around the trees will be monitored for root colonization and soil phosphate. Fifty soil samples were collected from fumigated and non-fumigated almond trees. Roots were sorted out for DNA extraction using PowerSoil DNA isolation kit. Primers from AM fungal ribosomal genes were used for generating polymerase chain reaction (PCR) fragments. Fragments were cloned and subjected to DNA sequencing. Sequencing data were blasted to a National Center for Biotechnology Information (NCBI) database for facilitating AM fungal identification. Soil phosphate concentrations were determined. Phosphate was extracted from the soil using the Olsen extraction method. The average phosphate concentration was 33 ppm. It made little difference whether the samples where fumigated (32 ppm) or non fumigated (34 ppm). It didn’t matter if trees were potted or bare root. Any change due to inoculation was minimal. Almond plants inoculated with commercial AM inoculum showed much higher colonization by Glomus intraradices than green house grown. The ADODR monitored this project through site visits, emails, and phone calls. The goal of the specific cooperative agreement is to develop practical applications of AM fungi to almond orchards. AM fungal colonization of almond roots may improve the health and drought resistance of the plants, which indirectly affects aflatoxin contamination of edible nuts. The research contributes directly to Objective 4 of the in-house project, "Develop biological control/intervention technologies using competitive or antagonistic microorganisms such as yeasts or bacteria that can be mass-produced and effectively utilized in a variety of pre- or post-harvest environments”.