Research Project: Genetics and Breeding of Lettuce, Spinach, Melon, and Related Species to Improve Production and Consumer-related Traits

Location: Crop Improvement and Protection Research

Project Number: 2038-21530-002-000-D
Project Type: In-House Appropriated

Start Date: Apr 11, 2018
End Date: Apr 10, 2023

Objective:
The focus of this research program is on quality traits, resistances to diseases, insects and abiotic stresses of lettuce, spinach and melon considered by the respective industries and the scientific community to be the most critical to production. We will develop elite germplasm and cultivars with improved quality and productivity, and new knowledge of the genetics and breeding of lettuce, spinach, and melon. Specifically, during the next five years we will focus on the following objectives. Objective 1: Discover and understand novel sources of resistance in lettuce to priority diseases and insects, tolerance to unfavorable abiotic factors (including physiological defects), and improved phytonutrient content; discover trait-linked molecular markers, and use these resources to develop and release improved lettuce germplasm and/or finished varieties. • Subobjective 1A: Corky Root • Subobjective 1B: Downy Mildew • Subobjective 1C: Fusarium Wilt • Subobjective 1D: Leafminer • Subobjective 1E: Lettuce Drop • Subobjective 1F: Phytonutrients • Subobjective 1G: Postharvest Quality • Subobjective 1H: Tipburn • Subobjective 1I: Impatiens necrotic spot virus • Subobjective 1J: Verticillium Wilt Objective 2: Discover and understand novel sources of resistance in spinach to new and emerging diseases (especially downy mildew) and insects (including leaf miner), and develop and release improved spinach germplasm and/or finished varieties. • Subobjective 2A: Spinach Downy Mildew • Subobjective 2B: Leafminer • Subobjective 2C: Linuron Herbicide Tolerance Objective 3: Discover and understand novel sources of resistance in melon to priority diseases and insect pests, and develop and release improved cantaloupe and honeydew germplasm and/or finished varieties with durable resistance. • Subobjective 3A: Resistance to Powdery Mildew • Subobjective 3B1: Resistance to Sweetpotato Whitefly • Subobjective 3B2: Determine inheritance of antixenosis • Subobjective 3B3: Introgression of Antixenosis

Approach:
1A: Corky Root. Approach: Combine resistances to corky root, leafminer, downy mildew, lettuce mosaic virus, & tipburn, & nutritional traits; pedigree selection & backcross for type. 1B: Downy Mildew. Approach: Map QTL in 2 F6 RIL populations & develop breeding lines with improved level of resistance. Cross resistant RIL & accessions; pedigree selection & backcross for type. 1C: Fusarium Wilt. Approach: Develop Fusarium wilt-resistance for the Salinas Valley by crossing advanced resistant desert selections with ‘Salinas’; backcross resistant F2 selection to ‘Salinas’, repeat to BC4F4. 1D: Leafminer Approach: Introgress leafminer resistance to different lettuce types by intercrossing resistance sources, then crossing them with breeding lines for combined resistances. Pedigree selection to F6. 1E: Lettuce Drop. Approach: Map QTL for resistance in a F6 RIL population; develop romaine lettuce with improved resistance using most resistant RIL & other accessions. Pedigree selection & backcross for type. 1F: Phytonutrients. Approach: Improve phytonutrient content of lettuce by crossing high carotenoid, anthocyanin, and antioxidant content sources with elite cultivars. Pedigree selection & backcross for type. 1G: Postharvest Quality. Approach: Develop tools to improve lettuce shelf life by combining automatic phenotyping, mapping & molecular markers for MAS; release breeding lines with extended shelf life. 1H: Tipburn. Approach: Develop romaine breeding lines with reduced incidence of tipburn using pedigree selection and backcrossing of advanced lines; select in desert and coastal environments. 1I: Impatiens necrotic spot virus. Approach: Identify resistance sources in Salinas & Pullman accessions in greenhouse tests; mechanical and thrips inoculations. Cross most resistant with elite cultivars. 1J: Verticillium Wilt. Approach: Identify higher levels of resistance to V. dahliae race 2 in Salinas & Pullman lettuce collection. Cross most resistant accessions with elite cultivars. 2A: Spinach Downy Mildew. Approach: Open-pollinated (OP) seed from resistant hybrid spinach cultivars will be OP with susceptible ‘Viroflay’; recurrent selection to combine resistances in OP lines. 2B: Leafminer. Approach: Breed for leafminer resistance against both stings and mines using recurrent selection starting with highest sources of resistance. 2C: Linuron Herbicide Tolerance. Approach: Recurrent selection to increase tolerance to Linuron in field tests. 3A: Resistance to Powdery Mildew. Approach: Introgress resistance in PI 313970 to races 1, 2, 3.5, 5, and S using F2 and F2:3 selections in greenhouse & field tests. Pedigree selection & backcross for type. 3B1: Resistance to Sweetpotato Whitefly. Approach: Compare antixenosis in 4 accessions using individual & group responses, odor-based assays, electrical penetration graphs, & candidate compounds. 3B2: Determine inheritance of antixenosis. Approach: Determine whether antixenosis in PI 122847 is simply inherited or quantitative using Y-tube assays of F2. 3B3: Introgression of Antixenosis. Approach: Introgress antixenosis in PI 122847 to elite western shipping type melon using backcrossing and inbreeding.