Harry Pink, Adam Talbot, Abi Graceson, Juliane Graham, Gill Higgins, Andrew Taylor, Alison C. Jackson, Maria Truco, Richard Michelmore, Chenyi Yao, Frances Gawthrop, David Pink, Paul Hand, John P. Clarkson & Katherine Denby

Theoretical and Applied Genetics July 2022; vol. 135: 2481–2500

Key message

We demonstrate genetic variation for quantitative resistance against important fungal pathogens in lettuce and its wild relatives, map loci conferring resistance and predict key molecular mechanisms using transcriptome profiling.

Abstract

Lactuca sativa L. (lettuce) is an important leafy vegetable crop grown and consumed globally. Chemicals are routinely used to control major pathogens, including the causal agents of grey mould (Botrytis cinerea) and lettuce drop (Sclerotinia sclerotiorum). With increasing prevalence of pathogen resistance to fungicides and environmental concerns, there is an urgent need to identify sources of genetic resistance to B. cinerea and S. sclerotiorum in lettuce. We demonstrated genetic variation for quantitative resistance to B. cinerea and S. sclerotiorum in a set of 97 diverse lettuce and wild relative accessions, and between the parents of lettuce mapping populations. Transcriptome profiling across multiple lettuce accessions enabled us to identify genes with expression correlated with resistance, predicting the importance of post-transcriptional gene regulation in the lettuce defence response. We identified five genetic loci influencing quantitative resistance in a F₆ mapping population derived from a Lactuca serriola (wild relative) × lettuce cross, which each explained 5–10% of the variation. Differential gene expression analysis between the parent lines, and integration of data on correlation of gene expression and resistance in the diversity set, highlighted potential causal genes underlying the quantitative trait loci.

See https://link.springer.com/article/10.1007/s00122-022-04129-5

Figure 7: Quantitative trait loci associated with reduced lesion size of B. cinerea or S. sclerotiorum. LOD scores from ‘stepwiseqtl’ multi-QTL selection models using the Haley–Knott algorithm, genotyping-by-sequencing markers and predicted mean lesion size from the detached leaf assay data for each pathogen are shown. Data relating to B. cinerea inoculation are shown in red, whereas those from S. sclerotiorum inoculation are shown in blue. Five significant QTL (qSs5,qSs8, qSs9, qBc7 & qBc9) were maintained in the final model after backwards elimination of insignificant loci. Boxes represent the 1.5LOD confidence intervals around the peak LOD of each QTL. The nine lettuce chromosomes are shown along the x-axis