ADVANTAGES OF MARKER-ASSISTED SELECTION (MAS) AND GENOTYPING IN THE DEVELOPMENT OF DETERMINATE, OPEN-FIELD-ADAPTED TOMATO HYBRIDS: A REVIEW

Abstract

Open-field tomato (Solanum lycopersicum L.), and in particular the processing and machine-harvested fresh-market crop, is built on the determinate growth habit. Determinate (self-pruning) hybrids form compact bushes that flower and ripen synchronously, allowing a concentrated, once-over harvest that is increasingly mechanised. Breeding a competitive determinate hybrid therefore means combining, in a single F1, a defined plant architecture suited to machine harvest, resistance to the field pathogen spectrum — in which bacterial spot and bacterial speck are prominent alongside the fungal, viral and nematode diseases — tolerance of open-field abiotic stress, and the fruit-quality profile the processing and fresh markets demand, notably high soluble-solids content, firmness, uniform ripening and colour. Assembling these largely unlinked, differently inherited traits by phenotype alone is slow and imprecise. Marker-assisted selection (MAS) and modern genotyping allow breeders to track resistance, architecture and quality alleles directly at the DNA level, at the seedling stage and independent of season or pathogen pressure. This review synthesises the molecular-marker resources relevant to determinate open-field tomato: the diagnostic markers for bacterial spot (Rx-3, Rx-4/Xv3, QTL-11) and speck (Pto), for the fungal, nematode and viral diseases, and for the architecture and quality loci that underpin mechanised production — self-pruning (sp), jointless-2 (j-2), fruit shape 8.1 (fs8.1) and the Brix-raising Lin5/Brix9-2-5 locus. Marker-assisted backcrossing, the pyramiding of linked resistance cassettes,and the prospects for genomic selection of quantitative field traits are discussed, and priorities for their adoption in the tomato breeding programme of the Andijan Scientific-Experimental Station are proposed.