370 Colchicine 



as illustrated by amphiploids of the Brassica comparium.^^' '^' '^'^' ^^• 



50, 19, 36. 37, 124, 125 



Three basic genomes are represented by diploid species of Brassica; 

 B. campestris, n = 10, or a: B. tiigra, n = 8, or b; and B. nleracea, n = 

 9, or c. There is some evidence of homology between a and r, but no 

 bivalents are formed between b and either a or c. The tetraploid 

 species B. carinata would have genomes ac cc; B. juncea aa bb; and B. 

 carinata bb cc. Accordingly, the hexaploid B. cJunensis X B. carinata 

 would have aa bb cc as genomes, or 27 bivalents. "^o 



Economically these genera of the Cruciferac comprise one of the 

 most important groups with world-wide distrilnition. The number of 

 amphiploids made at the tetraploid level has increased with the use 

 of colchicine. ^''- •^«' ■"• ^^^ ^""' ^3- ^'^- n''- 1'". i^i 



Synthesized amphiploids, comparable to the natural tetraploid 

 species of Brassica, can be hybridized readily and show possibilities 

 for selection in the succeeding generations. A large ninnber of pro- 

 genies are under study by Gosta Olsson at Svalof, Sweden. 



12.6: Other Interspecific Hybrids and Amphiploids 



Four species of Galeopsis, two diploid and two tetraploid, became 

 sul)ject to colchicine methods as soon as the drug was announced for 

 its polyploidizing action. Since tlie first Linnean species Galeopsis 

 tetrahit L. was produced by hybridizations with the two diploid 

 species, following doubling by gametic non-reduction, one of the first 

 uses for colchicine was a repetition of Galeopsis tetrahit L. By first 

 inducing autotetraploid G. pubescens and G. speciosa, the amj:)hiploid 

 was produced with little difficulty. Within a short time nuich poly- 

 ploid material was at hand for this genus. "-^ 



Cross combinations between diploid and tetraploid Galeopsis 

 usually fail, but genomes of dijiloid species can be hybridized at the 

 tetraploid level, using induced autotetrajiloids with natural tetra- 

 ploids.""' These crosses succeeded. Quantitative conditions control 

 the hybridization. More crosses were made to confirm this point."'* 



The octoploid number, 64, exceeds the optimum number for these 

 genotypes, for octoploid G. tetrahit and G. bifida are much inferior 

 to the natural tetraploids of these species.'^'' Basic cytogenetical data 

 have been increased many fold with the use of colchicine. 



Cytogenetical data from certain interspecific hybrids among Sola- 

 num suggested that there may be small structural differentiations be- 

 tween chromosomes of diploid species.^*' Such changes may have 

 significance in the evolution of species within Sohvitim. At least, 

 considerable data for interspecific hybrids have been accunudated 

 already, and more can be expected. 



The case presented for GTOSsypiuin proposing "cryptic structural 

 differentiation" as a speciation mechanism was recalled as an inter- 



