Development and Characterization of Genomic Resources for Prickly Lettuce

Prickly lettuce (Lactuca serriola L.) is a problematic weed of Pacific Northwest (PNW) and recently developed resistance to the auxinic herbicide 2,4-D. It is a troublesome and difficult to control weed in all crops in the PNW. There was no publically available simple sequence repeat (SSR) markers for L. serriola at the initiation of this project. Therefore, we developed SSR markers from expressed sequence tags (ESTs) for a variety of applications. A total of 15,970 SSRs were identified among 57,126 EST assemblies. SSR containing ESTs (SSR-ESTs) ranged from 6.23% to 7.87%, and SSR densities ranged from 1.28 to 2.51 kb^-1. Trinucleotide repeats were the most abundant SSRs detected. As a representative sample, 40 ESTs carrying class I SSRs (≥20 nucleotides) were selected for designing primers and were also searched against the dbEST entries for L. sativa and Helianthus annuus L. (≤10^-50; score ≥100). In silico analysis of the 40 SSR-ESTs indicated 82% conservation across species and 68% conservation across genera. Primer pairs synthesized for the 40 EST-SSRs were used to study genetic diversity among a collection of 22 L. serriola biotypes from the PNW. The developed markers are being applied to early generational mapping populations to understand complex traits like latex and rubber production and 2,4-D resistance.