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ARS Home » Pacific West Area » Salinas, California » Crop Improvement and Protection Research » Research » Research Project #437616

Research Project: Identifying the Basis of Lettuce Drop Resistance to Develop Cultivars with Superior Resistance

Location: Crop Improvement and Protection Research

Project Number: 2038-21530-002-27-R
Project Type: Reimbursable Cooperative Agreement

Start Date: Nov 1, 2019
End Date: Apr 30, 2022

Objective:
1: Elucidate the difference in cell wall composition between resistant and susceptible lettuce accessions in the greenhouse, as a prelude to developing new diagnostic techniques for detecting resistance to lettuce drop (Sclerotinia spp.) in lettuce. 2: Develop a new lettuce drop disease severity rating scale, aimed at using the scale for evaluating resistance to lettuce drop in lettuce in the field. Utilize historical data to address and validate the objective. 3: Establish the relationship between lettuce drop resistance and development. This will be aimed at developing a new diagnostic technique to indirectly determine resistance to lettuce drop in lettuce in the field by evaluating mechanical stem strength. 4: Genetically determine the relationship among resistance, development, and cell wall components, aimed at identifying carbohydrates associated with resistance/susceptibility to lettuce drop in lettuce in the field to use as a new diagnostic technique. Utilize historical data to address and validate the objective. 5: Identify specific cell wall polymers associated with resistance/susceptibility to enzymatic degradation by soft rot fungi that includes Sclerotinia spp. Data obtained from greenhouse and field experiments described for Objectives 1-4 will be used to achieve this objective. The project will incorporate historical data to address this objective. 6: Repurpose the enzymatic digestibility screening method to detect resistance to Sclerotinia spp. in California specialty crops.

Approach:
Select parents of a mapping population to use for other analyses after determining the difference between resistant and susceptible accessions. Eruption and/or PI251246 will be selected as the resistant parent(s). Batavia Reine Glaces (BRG) and/or Salinas will be chosen as the susceptible parent(s) of mapping population(s). Conduct experiment lettuce drop 1 (LD-1). Evaluate a mapping population derived from the two parents in the field. 160 recombinant inbred lines (RILs) will be planted in a field experiment at the Salinas research station as a replicated alpha design. The field will be artificially infested with S. minor, infected plants will be uprooted, and the variation in the extent of crown degradation of progenies of infected RILs will be examined. A scale will be developed and the lettuce drop severity will be categorized into classes. The scale will be used to evaluate all infected plants for disease severity. The data will be used to develop disease severity index (DSI). DSI will be used in genetic analysis to determine the feasibility of detecting lettuce drop resistance/susceptibility reliably using the newly developed disease severity rating scale. Conduct Cell wall 1 (CW-1) experiment. Analyze the crown tissue’s cell wall compositions (glycosyl composition, lignin content and monomer composition, and crystalline cellulose composition). This experiment will be carried out in conjunction with Objective 3 using the same methods and location as PD-1. About 3 to 5 cm of the crown tissue of plants used for stem strength measurement will be sampled and used to determine cell wall composition. Conduct Digestibility Assay 1 (DA-1) experiment. Subject the crown tissue of the mapping population to enzymatic digestibility assay. This protocol is developed to identify superior plant genotypes for enzymatic lignocellulose digestibility and specific genes affecting digestibility of biomass. This experiment will be carried out in conjunction with Objective 4 using the same methods and location as CW-1 except the samples will be used to determine cell wall digestibility.