Location: Crops Pathology and Genetics Research
Project Number: 2032-22000-017-022-R
Project Type: Reimbursable Cooperative Agreement
Start Date: May 1, 2021
End Date: Mar 31, 2023
1) Characterize the presence of Phytophthora species that may infect commercial orchard trees in waters conveyed by the Stockton East Water District (SEWD), California. 2) Assess potential agricultural risks posed by Phytophthora species present in water conveyed by SEWD.
Objective 1. Hypothesis: Species of Phytophthora known to be pathogens of fruit or nut tree orchards are present in waters conveyed by the Stockton East Water District (SEWD). Experimental approaches, specific research procedures: We will sample SEWD water and assay it for the presence and identity of Phytophthora species at monthly and biannual intervals from May 2021 to October 2022. Using filtrates and total DNA extracts of the SEWD water samples, we will conduct PCR-based amplification and PacBio-based high-throughput sequencing of the ITS 1 and 2 of the rRNA gene from Phytophthora. The sequences will be used to determine the presence and species-level composition of Phytophthora populations in the water. Also, we will use green pear fruits to bait and isolate species of Phytophthora species from SEWD waters. The isolates will be identified to species by ITS sequencing. Objective 2. Hypothesis: SEWD water can transmit viable inoculum of Phytophthora species to soil in commercial orchards, potentially impacting resident soil populations of the pathogens. Experimental approaches and specific research procedures: We will sample SEWD water after it has passed through on-farm irrigation systems (i.e., including the pump, filters, and irrigation emitters) but before it has contacted the orchard soil; the water will be intercepted by covered, modified 5-gal. buckets in which pear fruits will be used as bait for Phytophthora. Also, pear baiting and PCR-based assays will be used to determine whether composition of Phytophthora populations differs between soils irrigated with SEWD water vs. soils irrigated with well water. ITS sequencing will be used to assess the identity of Phytophthora spp. detected.