A Genetic Method for Detecting Induced Intergeneric Translocations.

M A N Y characters which would-be desirable in cultivated crops are known to exist in related species and genera. The most striking examples of such characters are the resistances to various diseases. Where hybridization can be achieved between the pertinent genera, attempts have been made to transfer genes for these desired characters into the genome of the cultivated species. Partially for this reason Triticum aestiuum L. has been hybridized with species of the other four genera of the sub-tribe Triticinae-uiz., Aegilops, Agropyron, Secale and Haynaldia. However, completion of such incorporation usually has not been achicl-ed owing to a lack of synapsis and crossing-over between the introduced chromosomes and the host chromosomes. The end result in a number of these cases has been an addition line in which the added foreign chromosome is present as an intact or telocentric chromosome or as an isochromosome. The added chromosome may be present as a monosome or as an homologous pair. Such addition lines containing foreign chromatin in addition to the normal complement are U-ually unsuitable because of undesirable genes present on the added chromosome and/or partial desynapsis of the added pair. Irradiation of addition lines has been employed in order to transfer the desired alien chromatin to a wheat chromosome. SEARS (1956) incorporated into the wheat genome a segment of Aegilops umbellulata Zhuk. chromatin, which confers resistance to wheat leaf rust (Puccinia recondita Rob. ex Desm.) . This was accomplished by irradiating plants which possessed the normal 42 wheat chromosomes plus an added Aegilops isochromosome consisting of the reduplicated chromosome arm which carried the gene or genes for wheat leaf-rust resistance. Pollen from X-irradiated plants was used in crosses with the wheat variety Chinese Spring, and resistant F, plants were examined cytologically. One line was isolated which possessed an intercalary translocation in which a piece of Aegilops chromatin, carrying the factor for resistance, had been inserted into a wheat chromosome. The newly synthesized chromosome exhibited normal male transmission.