Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/25/2015
Publication Date: 6/25/2015
Citation: Hayes, R.J. 2015. USDA lettuce breeding and genetics. University of California SeedCentral Forum, June 25, 2015, Salinas, California.
Technical Abstract: The lettuce industry of California requires continued development of improved, adapted cultivars to meet new disease and insect problems, changes in the market, and changes in growing procedures. The USDA lettuce breeding and genetics project aims to incorporate valuable traits into crisphead, mixed lettuce, and spring mix cultivars and breeding lines that are adapted to coastal California and low desert production conditions. For each project we seek to develop germplasm, information, and tools. Germplasm is released as selected populations, breeding lines, or cultivars possessing a new economically important trait or combination of traits. Our germplasm is publically released with no intellectual property protection, and given to seed companies at no cost so as to maximize the final number of new cultivars available to the lettuce industry. Within the last 10 years, this project has released numerous iceberg, romaine, and leaf type breeding lines with resistances to corky root, dieback, lettuce mosaic, Verticillium wilt, bacterial leaf spot, leafminer, and improved shelf-life. Information and tools are developed in parallel with breeding, and include knowledge of the inheritance and genetic diversity of economically important traits, new breeding or testing procedures, knowledge of lettuce biology or host-pathogen interactions, and molecular markers for marker assisted selection. These resources are distributed to other public and private scientists through peer-reviewed journal publications, with the goal of making the use of our released germplasm easier and more efficient. Ultimately, this increases the use of our germplasm by other breeding programs for development of new cultivars. Verticillium wilt, caused by the soil-borne fungus Verticillium dahliae, is a destructive disease of lettuce in California. The USDA has been conducting research to develop germplasm, tools, and information in order to develop resistant cultivars. Our research identified Verticillium resistance 1 (Vr1), which confers resistance to race 1 isolates but is defeated by race 2 isolates. Iceberg cultivars were released that carry Vr1. Race 2 isolates are predicted to increase in prevalence, and developing resistance to these isolates is a top priority. Screening over 800 accessions for resistance to race 2 has identified three accessions with partial resistance. To date, complete resistance is not known. Partially resistant accessions were intercrossed with each other and a susceptible cultivar in order to study the inheritance of resistance to race 2. In populations of F3 families derived from these crosses, resistance is quantitatively distributed and appears to be conditioned by multiple genes. The segregation and high resistance found in some crosses is useful for identifying QTLs and breeding resistant cultivars.