STATE OF THE ART OF GENETICS AND BREEDING OF PROCESSING TOMATO: A COMPARISON OF SELECTION BASED ON MOLECULAR MARKERS, BIOCHEMICAL PATHWAY, AND PHENOTYPE FOR THE IMPROVEMENT OF FRUIT COLOR AND JUICE VISCOSITY

The objective of the research described in this paper was to compare the efficiency of selection based on indirect methods to selection based on trait performance. We estimated the effect of indirect selection for the improvement of tomato fruit color and juice viscosity. For fruit color, we compared marker-assisted selection to methods based on objective measurements of color. For juice viscosity we compared selection based on pectin methyl esterase (PME) activity to selection based on laboratory viscosity measurements on samples from replicated trials. Indirect selection was found to be 20% as effective for viscosity, 43% as effective for L and 38% as effective for Hue when selection was based on the mean from replicated trials. In early generations when selection was based on a single plant, markers linked to quantitative trait loci (QTL) for color provide a gain in efficiency that exceeds indirect selection by two fold for both L and Hue. Selection for viscosity based on PME activity was 40% as efficient and does not offer an advantage even in early generations. The activity of PME was significantly influenced by a locus on Chromosome 7, but this locus represents a minor QTL for juice viscosity explaining 11% of the phenotypic variance. We conclude that indirect selection has a role in early generation selection. In none of the cases examined does indirect selection replace selection based on trait performance in later generations. Selection based on phenotype in replicated trials of families, breeding lines, and varieties remains an essential strategy for improving fruit quality.