Location: Crop Improvement and Protection Research
Project Number: 2038-21530-003-027-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Nov 1, 2025
End Date: Jun 30, 2028
Objective:
California’s Monterey County harvests 100,000 acres of lettuce (Lactuca sativa L.) annually at a value of $1.2 billion. In recent years, incidence of Impatiens Necrotic Spot Virus (INSV) has increased significantly causing devastating losses to lettuce production. Genetic resistance is the most economical and environmentally sound control method, but only partial resistance to INSV has been identified. Therefore, further characterization of this resistance and development of improved lettuce germplasm is imperative. With the goal of developing molecular tools to release improved germplasm, our objectives are to: 1) identify genomic regions linked to INSV resistance in Eruption and Anais and develop marker assisted selection assays, 2) dissect the role of thrips preference, lettuce secondary metabolites, and virus localization in INSV resistance, and 3) develop and release improved romaine germplasm. Success will be indicated by releasing new lettuce germplasm, developing marker assisted selection assays, publications, citations, and requests for seeds and information.
Approach:
Nov 2025 to Apr 2026: Germplasm from Populations A and B will be evaluated under INSV in controlled, greenhouse conditions. INSV symptoms in lettuce will be rated on a 0 to 5 scale. ELISA will be run to determine virus presence. Results will be statistically analyzed. The most resistant lines will be selected and advanced to further stages of development. Leaf tissue will be collected from each individual for DNA extraction and genotyping with a 3K DArTag panel.
May 2026 to Oct 2026: Germplasm from Populations A and B will be grown under field conditions following standard growing practices with natural INSV and thrips pressure. INSV incidence and severity will be measured along with horticultural traits such as leaf color and head type. Results will be statistically analyzed. INSV resistant lines with desirable horticultural traits will be selected and advanced to further stages of development.
Nov 2026 to Apr 2027: QTL analysis on genotype and phenotype data for Populations A and B will be run. Marker assisted selection assays will be developed for Eruption and Anais sources of resistance. Select lines from Populations A and B will be evaluated under INSV in controlled, greenhouse conditions. Plants will be sampled before and after inoculation to quantify polyphenol content and lettuce secondary metabolites associated with plant defense. Plants will be sampled after inoculation to quantify the number of adult and immature thrips as a measure of feeding and reproductive preferences, respectively. Tissue will be sampled from the root, crown, and leaves of plants to determine virus localization by ELISA and/or qPCR analysis.
May 2027 to Oct 2027: Marker assisted selection assays will be validated for Eruption and Anais sources of resistance. Select lines from Populations A and B will be grown under field conditions following standard growing practices with natural INSV and thrips pressure. INSV incidence and severity will be measured along with horticultural traits such as leaf color and head type. Plants will be sampled before and after infection to quantify polyphenol content and lettuce secondary metabolites associated with plant defense. Plants will be sampled after inoculation to quantify the number of adult and immature thrips as a measure of feeding and reproductive preferences, respectively. Tissue will be sampled from the root, crown, and leaves of plants to determine virus localization by ELISA and/or qPCR analysis.
Nov 2027 to Jun 2028: Write publication on characterization of resistance to INSV. Release data and seeds of selected breeding lines to the public and seed companies.