Location: Crop Improvement and Protection Research
Project Number: 2038-21530-003-028-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Nov 1, 2025
End Date: Jun 30, 2028
Objective:
Fusarium wilt, caused by the soil borne fungal pathogen Fusarium oxsporum f. sp. lactucae (FOL), is one of the most limiting factors for lettuce production worldwide, including the United States. Out of the four recognized races, only race 1 is known to exist in the United States. However, concerns have recently increased among lettuce growers in the Salinas Valley of California due to changes in pattern of Fusarium wilt disease. In order to characterize pathogen, we collected samples, recovered the fungus, and conducted the pathogenicity test. Our test confirmed the presence of a more aggressive novel race that pose a serious risk for lettuce production. Genetic resistance is the most sustainable strategy to minimize the risk. Our objectives are to 1) Identify QTL and develop molecular markers closely linked to the resistance gene; 2) Elucidate differential expression of genes in resistant and susceptible genotypes; and 3) Develop lettuce germplasm with broad spectrum resistance against multiple races.
Approach:
Nov 2025 – Oct 2026: B x E biparental mapping population comprising 162 recombinant inbred lines (RILs) will be evaluated for resistance against race 1 and novel aggressive isolates of FOL in controlled conditions. Foliar and root symptoms will be rated using a 1 – 4 rating scale. Phenotype data will be statistically analyzed for selecting the most resistant RILs.
Nov 2025 – Apr 2026: DNA extraction of 164 samples (162 RILS + 2 parents) will be completed and sent to Breeding Insight (Cornell University, NY) for genotyping the mapping population with DArTag markers panel. A high-density genetic linkage map will be constructed using polymorphic markers.
May 2026 – Oct 2026: We will collect tissue samples (2 parents + 5 most resistant RILs + 5 most susceptible RILs) for RNA-seq analysis at three timepoints (the first sampling at Pre-inoculation, and the second and third sampling at 10 and 20 days post-inoculation, respectively). Samples will be flash frozen in liquid nitrogen and preserved in freezer at -80 °C until further processing.
Nov 2026 – Apr 2027: QTL analysis will be performed using phenotypic data and a high-density linkage map. Resistant Allele specific functional marker will be developed for marker-assisted selection.
Nov 2026– Apr 2027: RNA extraction of 12 samples (2 parents + 5 most resistant RILs + 5 most susceptible RILs) will be completed and differential gene expression analysis will be performed to identify candidate gene. A qPCR assay will be designed for candidate gene expression involved in Fusarium wilt resistance.
May 2027 – Oct 2027: Validation of molecular markers and qPCR assay will be performed using an independent population (Romabella × Patriot) to ensure utility of molecular tools for screening germplasms for Fusarium wilt resistance.
Nov 2027 – June 2028: Publish research outcomes on characterization of resistance to Fusarium wilt and newly developed molecular tools. Release data and seeds of selected Fusarium wilt resistant breeding lines to the public and seed companies.