Location: Crop Improvement and Protection Research
Project Number: 2038-22000-019-082-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Sep 27, 2026
End Date: Sep 26, 2028
Objective:
Objective 1: Characterize the variation in cavity spot incidence and severity as well as the composition of the cavity spot pathogen population in response to soil nitrogen concentration.
Objective 2. Characterize the soil microbial communities in response to soil nitrogen with special attention to beneficial arbuscular mycorrhizal fungi.
2a. Develop methods to quantify abundance of beneficial arbuscular mycorrhizal fungi in soil and carrots.
2b. Characterize the soil microbial community in response to soil nitrogen concentration.
Approach:
Objective 1. Paired carrot and soil samples will be collected at mid-season and crop maturity from a conventional research plot in the Bakersfield region. The oomycete pathogens will be isolated from carrot samples using semi-selective media and identified using PCR and Sanger sequencing. Soil nitrogen content will be measured using standard protocols at a third-party laboratory. Variation in pathogen abundance and composition, disease incidence and severity, and nitrogen concentration will be tested using analysis of variance or a non-parametric alternative. In addition, the relationship between pathogen abundance and soil nitrogen concentration will be tested using linear regression.
Objective 2a. Sequence data from target AMF species will be used to design qPCR primers and probes. Specificity and sensitivity of the qPCR assays will be evaluated using standard molecular biology protocols. Finalized assays will be used to measure variation of AMF species in soil from conventional and organic carrot farms collected from prior research. Differences in the abundance of AMF species between conventional and organic farms will be tested using T-tests or a non-parametric alternative.
Objective 2b. The microbial composition of carrot rhizosphere soil samples taken before and after various nitrogen treatments will be determined using amplicon sequencing. Data will be used to understand the impact of nitrogen on the carrot microbiome and soil health. Methods developed under Objective 2a will be used to evaluate the effect of the nitrogen treatments on the abundance of AMF known to interact with and carrot health and productivity.