300 Colchicine 



Aegilops other than A. squarrosa. Third, the combined genomes A 

 and D united with various species oi Agropyron would lead to ways 

 for introducing genes from the latter genes to the present B genome 

 of hexaploid wheat. Fourth, the synthesized B and D genomes added 

 to diploid Triticum would allow transfer of einkorn characters to the 

 hexaploid wheat. Such a program is exceedingly involved; however, 

 it merits serious attention, (cf. Chapter 11. Ref. No. 49) . 



72.2-5; Triticum aestwum L. X ^ecaJe cereale L — Triticale. In 

 1876 the first hybridization between wheat and rye was made. About 

 4 per cent of hybridizations between wheat and rye give some idea 

 of the success to be expected. Under unusual circumstances a fertile 

 56-chromosome Fo can be obtained. An unreduced gamete most 

 likely explains the mode of doubling. Since colchicine became avail- 

 able, new methodsii^ have been developed to increase the production 

 of Triticnles.^^- ^■'- "'' 



There are five well-known strains,2i (1) Rimpau 1891, (2) Meis- 

 ter 1928, (3) Lebedeff 1934, (4) Taylor 1935, and (5) Miintzing 

 1936. Since 1936 many more have been made. Actually no accurate 

 record can be given because of the number of unpublished cases. 



Biologically the 56-chromosome plant is of interest because the 

 constant number has been maintained in the Rimpau strain after 

 more than fifty generations. Backcrosses to wheat give some index 

 of the stability that Tritirales can maintain. The 56-chromosome 

 plants survive better, are taller, and maintain a stable genetic 

 mechanism in spite of some meiotic irregularities.21 At meiosis in the 

 Fi very little pairing has been observed, 0-3 pairs; and upon dou- 

 bling, mostly bivalents are seen with as high as 6 unpaired chromo- 

 somes in some strains. There is practically no homology between the 

 wheat and rye chromosomes. -^ 



Among backcross progenies a pair of rye chromsomes have been 

 substituted for one pair of wheat chromosomes (cf. Chapter 14, Ref. 

 No. 37) , so there would appear to be slight possibility for gene ex- 

 change under selection. In nature the Triticale could evolve as a new 

 species because there is some degree of difference between the strains 

 regarding fertility and segregations in the subsequent generations. 

 However, the Triticale would remain at the octoploid level, and con- 

 sequently, a group ol new species could evolve with 56 chromo- 

 somes^i (cf. Chapter 14, Ref. No. 37, 27, 46, 51) . 



Economically these species bring into one plant two of the world's 

 important bread-producing species, wheat and rye. Since doubling 

 the chromosomes can be done with colchicine, a serious attempt to 

 improve Triticale on a large scale should have possibilities. 



An all-out attack on this ])roblem was begun in 1939 in Holland; 

 it involved the processing of hundreds and even thousands of combi- 

 nations.ii^ A new method of clonal division and vegetative propa- 



