Introgression libraries with wild relatives of crops

The narrowgenetic base of many crops raises concerns about the prospects for continued genetic gains necessary to meeting the increasing demand for agricultural output in an age of climate changes. The development and application of the introgression line (IL) breeding approach was proposed to more efficiently harness the genetic potential stored in exotic germplasm for the improvement of agricultural performance of elite germplasm, thereby expanding the genetic base of our crops. In tomato, the IL approach has been used for almost two decades, and the studies conducted on the Solanum pennellii LA0716 ILs (the founding "exotic library") using cutting-edge 'omics' platforms have clearly demonstrated the effectiveness of these congenic and permanent resources in fundamental biology, and for exploring and utilizing the hidden breeding potential of wild species for practical use in agriculture. Since the pioneer studies conducted in tomato, collections of ILs representing different fractions of the exotic parent genome have been developed for a wide range of crops. The results indicate that crop wild relatives are a rich reservoir of potentially valuable alleles, many of which would not have been predicted from the mere phenotypes of the wild plants. Therefore, exotic libraries, combined with the ever-growing body of genomics tools, are expected to further improve the efficiency with which the nature of quantitative trait variation will be unveiled and wild relatives of crops will contribute to face future breeding challenges.