296 Colchicine 



against natural T. spelta.^""- '" On the contrary, a close homology was 

 suggested. There was more difference between synthetic T. spelta 

 and natural T. spelta when amphiploids were obtained after gametic 

 doubling''"* than those irom somatic doubling."" 



Crossing with Aegilops squarrosa so improved the plant and the 

 grain that one might expect a naturally occurring fertile plant like 

 the resulting hybrid to be recognized as a new variant."" The geo- 

 graphic range of A. squarrosa should show in general where the 

 original hybridization took place.''"' This species grows today in the 

 northwestern Himalayas, the Caucasian region, and over an area 

 where hexaploid wheats could have originated as a result of the con- 

 tact of A. squarrosa with tetraploid species of Triticuui. Diploid 

 Aegilops, known as goat weed, is a very unpromising agricultural 

 plant;!"^ yet its contribution to connnercial wheat by a species like 

 A. squarrosa must be very specific and is apparently necessary. The 

 genome is called the D genome."'" 1 herefore, hexaploid wheats are 

 now identified by genomes A, B, and D, each representing a genus and 

 each sharing one-third of the 42-chromosomes.i""- ''^- '^^ An isolating 

 mechanism has been discovered in Triticuin associated with the D 

 genome. ""* 



Between the dawn of agriculture and some time not too long ago, 

 the hexaploid wheat evolved. Exactly when and how many times the 

 hexaploid species appeared remain luisolved problems. Let us say 

 at some time between 2000 and 10,000 years ago. Or perhajjs the 

 cross between diploid Aegilops squarrosa and tetraploid wheat is 

 happening today. Ihe amjjhijjloid Triticum jyersicum X Aes,ilo}ys 

 squarrosa, which is very similar to hexaploid Triticuyn, is a species 

 obtained from Russia.^^ If more hexaploid cases could be found in 

 the areas where Aegilops squarrosa grows, sucli additions to our 

 knowledge would be of great interest. •'''' 



We know there are parts to the story that must be sketched with 

 certain reasonable assumj)tions. It was remarkable that two research 

 teams,-"'**' '^" working entirely inde))cndent of each other, came so close 

 to each other in an agreement that Aegilops squarrosa is suspected 

 as one of the diploid species. 



Evidence that some other diploid species of Aegilops contributed 

 to wheat now becomes a burden of ])roof by using a cross involving 

 other species, or else by other methods to demonstrate how the hexa- 

 ploid wheats came into existence when they did. For the present at 

 least, the independent contributions of Japanese and American geneti- 

 cists that Aegilops squarrosa contributed genome 1) still stands. 



An important character of Triticuin aestivum is the free-threshing 

 feature. Ihe synthetic T. spelta, like natural T. spelta, was an in- 

 vested type. How the free-threshing types such as T. aestii'uni L. 



