text: Furthermore, breeders of modern tomato cultivars typically strive to produce tomato plants exhibiting improved yield, shelf life, size, and tolerance/resistance to various environmental pressures, including disease. However, these breeding efforts have yielded unintended negative consequences on various tomato fruit attributes. For instance, linkage drag is a phenomenon that has been responsible for alterations in the metabolism of the tomato fruit. Linkage drag describes the introduction of an undesired trait or allele into a plant during backcrossing. This trait/allele is physically linked (or is very close) to the desired allele along the chromosome. In introducing the beneficial allele, there exists a high likelihood that the poor allele is also incorporated into the plant. Thus, breeding efforts attempting to enhance certain traits (for example: larger fruit size) have unintentionally altered production of chemicals associated with, for instance, nutritional value and flavor.
  Breeders have turned to using wild tomato species as a source of alleles for the introduction of beneficial traits into modern tomato varieties. For example, wild tomato relatives may possess higher amounts of fruit solids (which are associated with greater sugar content) or resistance to diseases caused by microbes, such as resistance towards the early blight pathogen Alternaria solani. However, this tactic has limitations, for the incorporation of certain traits, such as pathogen resistance, can negatively impact other favorable phenotypes, such as fruit production.