Genetic architecture of tipburn resistance in lettuce

Authors: MACIAS GONZALEZ, M - Enza Zaden; TRUCO, M - University Of California; BERTIER, L - University Of California; JENNI, S - Agriculture And Agri-Food Canada; Simko, Ivan; Hayes, Ryan; MICHELMORE, R - University Of California

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2019
Publication Date: 7/15/2019
Citation: Macias Gonzalez, M., Truco, M.J., Bertier, L., Jenni, S., Simko, I., Hayes, R.J., Michelmore, R.W. 2019. Genetic architecture of tipburn resistance in lettuce. Theoretical and Applied Genetics. 132(8):2209–2222. https://doi.org/10.1007/s00122-019-03349-6.
DOI: https://doi.org/10.1007/s00122-019-03349-6

Interpretive Summary: Tipburn is a physiological disorder characterized by necrotic lesions on leaf margins, and is triggered by environmental factors that are not completely understood. In commercial lettuce, even low incidence of tipburn renders the heads unsalable. In addition, tipburn provides entry points for postharvest storage decay organisms that reduce shelf life and culinary quality. We conducted research to elucidate the genetic control of resistance to tipburn in lettuce using seven lettuce populations, derived from different combinations of parents that differed in their susceptibility to tipburn; testing them in multiple environments and years to identify quantitative trait loci (QTL) for tipburn. Core height, head firmness, head closure, leaf crinkliness, plant fresh weight, and leaf savoy were also analyzed to investigate whether QTL for these morphological traits collocated with QTL for tipburn, which would be indicative of pleiotropic effects. Twenty-three major, intermediate, and minor unique QTL for tipburn were identified in one or more populations scattered throughout the genome. Two major QTL for tipburn incidence were identified in linkage groups (LG) 1 and 5, which determined up to 45 and 66% of the phenotypic variance. The major QTL in LG 1 collocated with the head firmness QTL. The major QTL in LG 5 collocated with the QTL for core height, leaf crinkliness, and head firmness. Further research is needed to determine whether these associations are due to pleiotropic effects of the same gene or if the genes determining these traits are tightly linked. The beneficial alleles at the QTL in LG 1 and 5 are present in the widely grown cultivar Salinas, the genotype sequenced for the reference genome assembly. These QTL are good targets to identify genes controlling tipburn reaction as well as regions for marker-assisted selection to improve resistance to tipburn in lettuce.

Technical Abstract: Tipburn is a physiological disorder in lettuce that is thought to be caused by a localized deficiency of calcium in leaf tissues. To elucidate the genetic architecture of resistance to tipburn in lettuce, seven recombinant inbred line (RIL) populations were analyzed in multiple environments and years to identify quantitative trait loci (QTLs) for tipburn. Core height, head firmness, head closure, leaf crinkliness, plant fresh weight, and leaf savoy were also analyzed to investigate whether QTLs for these morphological traits collocated with QTLs for tipburn, which would be indicative of pleiotropic effects. Twenty-three major, intermediate, and minor unique QTLs for tipburn were identified in one or more populations scattered throughout the genome. Two major QTLs for tipburn incidence were identified in linkage groups (LGs) 1 and 5, which determined up to 45 and 66% of the phenotypic variance. The major QTL in LG 1 collocated with the head firmness QTL. The major QTL in LG 5 collocated with the QTL for core height, leaf crinkliness, and head firmness. Further research is needed to determine whether these associations are due to pleiotropic effects of the same gene or if the genes determining these traits are tightly linked. The beneficial alleles at the QTLs in LGs 1 and 5 are present in Lactuca sativa cv. Salinas, the genotype sequenced for the reference genome assembly. Therefore, these QTLs are good targets to identify genes causing tipburn as well as regions for marker-assisted selection to improve resistance to tipburn in lettuce.