Genomic mapping of a major effect recessive allele controlling high levels of metribuzin tolerance on tomato chromosome 1

Metribuzin is a large-spectrum herbicide extensively employed in the tomato crop. Even at recommended doses and suitable application times, many cultivars might display varying degrees of metribuzin toxicity. Hence, the deployment of cultivars with genetic tolerance could facilitate weed management. The inbred line ‘CNPH–0498’ (derived from ‘UGA-1113-MT’) displayed high levels of metribuzin tolerance. Inheritance studies were carried out using populations derived from the cross ‘Viradoro’ (a metribuzin-sensitive cultivar) × ‘CNPH–0498’. The segregation patterns strongly indicated that tolerance is under control of a major effect recessive allele, tentatively named as mtz . Bulked segregant analysis was used to identify a scorable PCR marker (OP-Z11-950) linked in repulsion phase to mtz . Cloning and sequencing allocated OP-Z11-950 amplicon on chromosome 1. Denser genome-wide linkage mapping was carried out with 1056 co-dominant solCAP SNP markers genotyped with the EMBRAPA Multispecies 65K chip. The two closest SNP markers were positioned at 3.78 and 21.4 cM distance, flanking the tolerant locus at the bottom arm of chromosome 1. Multiple-round genomic scans confirmed mtz as the only locus segregating with the metribuzin tolerance in a mapping population of 501 F ₂ individuals. Haplotype analysis revealed a success rate of 91.9% in marker assisted selection for high levels of tolerance. The genetic mapping of mtz is the first step to understand the physiological bases of the tolerance and to move towards the large-scale manipulation of this trait in breeding programs.