# Integrative path modeling and QTL mapping identify maturity, stem strength, and cell wall composition driving lettuce resistance to Sclerotinia minor

## TL;DR

Researchers identified genetic factors in lettuce that improve resistance to a disease while reducing early bolting, a key step for breeding healthier crops.

## Contribution

The study reveals novel genetic loci and mechanisms linking lettuce maturity, stem strength, and disease resistance.

## Key findings

- Resistance to Sclerotinia minor is associated with earlier bolting, stronger stems, and higher pentose content.
- Three QTLs on linkage groups 2, 6, and 7 are consistently linked to resistance, bolting, and stem mechanical strength.
- A callose synthase gene on LG7 is a key candidate for resistance, independent of maturity-related genes.

## Abstract

Lettuce (Lactuca sativa) is highly vulnerable to Sclerotinia minor, the pathogen causing lettuce drop. Breeding for resistance is the most effective control strategy; however, full resistance has not been achieved, and current partial resistance sources are often linked with undesirable traits, such as early bolting. This study aimed to unravel the genetic basis of partial resistance to S. minor and its relationship with plant maturity (bolting), stem mechanical strength (SMS), and cell wall composition (CWC) using a recombinant inbred line (RIL) population derived from a cross between the susceptible iceberg cv. ‘Salinas’ and the resistant oil-seed accession PI 251246. Field evaluations indicated that resistance was linked to earlier bolting, stronger stems, and higher pentose content. Path analysis demonstrated that earlier-maturing plants exhibited increased resistance through enhanced SMS and modified CWC, particularly with higher xylose and lower arabinose levels. Further analysis indicated a significant relationship between syringyl lignin content and resistance, especially in plants with varying bolting responses. Three key quantitative trait loci (QTLs) on linkage groups (LG) 2, 6, and 7 were consistently associated with resistance, bolting, and SMS. Importantly, residual QTL analysis revealed that the resistance locus on LG7 acted independently of maturity, suggesting a distinct resistance mechanism. Callose synthase emerged as a key candidate gene within the LG7 resistance QTL, located near - but distinct from - genes associated with plant maturity and flowering. These findings provide valuable insights into decoupling resistance from early bolting, suggesting a pathway for breeding lettuce cultivars with improved disease resistance and delayed bolting.

The online version contains supplementary material available at 10.1038/s41598-025-03775-1.