Section 8 — Cytatoxonomy and Experimental Taxonomy 



extensive chromosomal differentiation from all 

 other diploid species. The nature of this differ- 

 entiation and its significance in the study of 

 species relationships in diploid, tetraploid and 

 hexaploid Avenae will be discussed. 



8.12. Some Experimental Data on the Range of the 

 Species Hordeum spontaneum C. Koch emend. 

 Bacht. F.Kh. BAKHTEYEv(Leningrad,U.S.S.R.). 



Until lately it was thought that Hordeum spon- 

 taneum includes only two-rowed forms. How- 

 ever, the discovery in 1958 in the Turkmenian 

 Soviet Republic territory of a six-rowed wild- 

 growing barley, conditionally called Hordeum 

 lagunculiforme Bacht., made it necessary to re- 

 consider this question, especially as somewhat 

 later similar six-rowed wild barleys were found 

 in the Azerbaijan and Tadjik Republics, as well 

 as in some other localities of the U.S.S.R. 



The author'sown large original materials ena- 

 bled the conclusion to be drawn that H. lagunculi- 

 forme is actually not an independent species, as 

 one could suppose up to the present time, but 

 represents another extreme link in the system 

 of the species Hordeum spontaneum C. Koch 

 emend. Bacht. The latter includes four strains: 

 (1) var. spontaneum (= H. spontaneum var. itha- 

 burense [Boiss.] Nabelek); (2) var. ischnatherum 

 (Cosson) Thell.; (3) var. proskowetzii Nabelek; 

 (4) var. lagunculiforme Bacht. Thus, we may 

 consider it proved that Hordeum spontaneum 

 C. Koch emend. Bacht. includes not only two- 

 rowed individuals, as was thought since the first 

 description of this species by C. Koch in 1848, 

 but that it involves also six-rowed forms. 



The above data should be regarded not only 

 as a new illustration to the splended theoretical 

 conception of N. I. Vavilov, "The Linnean 

 species as a system", but as a real basis for fur- 

 ther experimental investigations into the origin, 

 phylogeny, and evolution of cultivated barley. 



In principle one may probably agree with the 

 conception, that the initial six-rowed and two- 

 rowed cultivated barley forms originated from 

 the genetically nearly-related Hordeum sponta- 

 neum C. Koch emend. Bacht. 



Hordeum halophilum and H. muticum are two 

 diploid sympatric species distributed along the 

 mountains from Peru to Argentina. The mor- 

 phology, chromosomal meiotic behaviour and 

 karyotypes of these two species and of their 

 natural sterile hybrid have been studied. 



Meiosis in the parental strains is regular or 

 nearly so. H. halophilum had the following mean 

 chromosome associations: 6-99 II, 002 I, and 

 H. muticum 6*81 II, 0-38 I, while the hybrid had 

 002 IV, 001 III, 6-63 II, 0-62 I. The meiotic be- 

 haviour of the chromosomes in the hybrid as 

 well as the karyotypes indicate that the genomes 

 of both species are largely homologous. They 

 differ, however, in at least one reciprocal trans- 

 location and one paracentric inversion. 



The main isolating mechanisms between both 

 species seem to be the slightly different edaphic 

 requirements and the absolute sterility of the 

 hybrids that makes gene interchange impossible. 



At anaphase II 8.5 per cent of the cells had 1-3 

 "dineocentric" bridges. These originated from 

 activation of usually terminal or moie rarely 

 interstitial neocentromeres, each stretching the 

 laggard and causing the formation of a bridge, 

 with the centric region attenuated and stretched. 

 This phenomenon has already been observed in 

 other grass hybrids (Hunziker and Covas, Rev. 

 Investig. Agric. 9 (3), 155-175, 1955; Walters, 

 M. S., Univ. of Calif. Public, in Bot. 28 (6), 335- 

 447, 1957, etc.). 



8.13. Evolutionary Relationships between Two South 

 American Species of Hordeum. Juan H. Hun- 

 ziker and Leonor Maumus (Buenos Aires, 

 Argentina). 



8.14. Genome Construction Within the Triticinae. 



L. E. Evans (Winnipeg, Canada). 



The two synthetic amphiploids Triticum durum 

 var. Carleton — Aegilops squarrosa (AABBDD) 

 and Triticum durum var. Stewart — Agropyron 

 elongatum (AABBEE) when crossed produced a 

 partially fertile F- having an average meiotic 

 metaphase configuration of 14- + 14 11 . By means 

 of cytological selection in the F2 to F7 generations 

 32 moderately stable, fertile, hexaploid derivates 

 were obtained from this cross. These individuals 

 should possess the 14 pairs of T. durum chromo- 

 somes (AABB) plus a mixture of Aegilops (DD) 

 and Agropyron (EE) chromosomes in the third 

 genome. Several of these lines were backcrossed 

 to the original hexaploid parents and the back- 

 cross Fi plants were cytologically studied in 

 order to determine the number of Aegilops and 

 Agropyron chromosomes in the third genome. 

 The combinations that theoretically could be 

 produced range from 7D+0E to 7E+0D chro- 

 mosomes and the results indicate that the entire 

 range may be produced. The identity of the spe- 



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