Case History in Germplasm Introgression: Tomato Genetics and Breeding Using Nearly Isogenic Introgression Lines Derived from Wild Species

This chapter demonstrates that nearly isogenic lines (NILs) representing the entire genome provide a more comprehensive view of the inheritance of traits showing continuous variation than conventional segregating populations. NILs for quantitative trait loci (QTL) constructed in elite genetic backgrounds enhance the rate of variety development through the union of QTL identification and plant breeding. Fruit mass and fruit total soluble solids, measured in degrees Brix, have been analyzed in many interspecific tomato crosses. Gene action of the QTL detected using the introgression line (IL) population was determined by comparing the homozygous ILs to their hybrids with the recurrent parent. Mendelian factors underlying quantitative traits in an interspecific tomato cross were compared in F2 and F3 generations of the same population. Similar map positions of major QTL among different crosses, species and even taxa have led to the postulation that many QTL are conserved.