ABSTRACT
Chromosome engineering had its inception in the pioneering contribution of Sears, who utilized irradiation as a means to translocate a gene for leaf rust resistance from Aegilops squarrosus to wheat. The establishment of aneuploid lines permitted manipulation of individual chromosomes and genetic analysis of wheat and its relatives. There are certain limitations in securing a full set of addition lines of one alien genome. The principal problems are—genetic sterility associated with certain chromosomes, genocidal effects under certain combinations, and even poor pollen transmission in certain genotypes. Substitution lines are those in which a chromosome or a complete genome of an alien species has been substituted in the target recipient. Such chromosome substitution with foreign gene can also be obtained as a special strategy without using addition lines. In order to secure translocations of alien gene, substitution or addition lines, as used in wheat, are intermediate steps. Several strategies have so far been adopted for securing translocations.
