Comparison of a set of allelic QTL-NILs for chromosome 4 of tomato: Deductions about natural variation and implications for germplasm utilization

Quantitative Trait Locus (QTL) allelic variation was studied by analyzing n ear-isogenic lines (NILs) carrying homologous introgressions on chromosome 4 from three green-fruited wild tomato species. The NILs affect agronomic ( yield, brix, fruit weight) and fruit (fruit shape, color, epidermal reticul ation) traits in a similar manner. However, significant differences were de tected in the magnitudes of the effects, the dominance deviations and epist atic interactions, indicating that those species carry different alleles fo r the QTL. As the QTL did not show any interaction across environments, gen etic backgrounds or other QTLs, it can be used to introduce novel genetic v ariation into a broad range of cultivars. Analysis of new recombinant NILs showed that fruit traits are controlled by several linked genetic loci, whe reas multiple genetic loci control the agronomic traits within the original introgression. The hypothesis that QTLs may be composed of multiple linked genes can not be rejected prior to implement projects for QTL isolation an d cloning. Loci involved in color enhancement could not be related to any k nown gene involved in the carotenoid biosynthesis pathway, therefore it is hypothesized that the function of those loci must be related to the genetic regulation of the carotenoid biosynthetic pathway.