Production, morphology, and cytology of induced polyploids of Elymus canadensis L

To examine germplasm potential for forage production, different ploidy levels of Elymus canadensis were induced and their genomic constitutions were modified. The chromosome numbers of hybrids derived from crosses between Elymus canadensis (SSHH) and Psathyrostachys juncea (NN) and Secale cereale (RR) were doubled to produce allopolyploids. Somatic tissue culture and subsequent interploidy hybridization were applied to produce autoallopolyploids of E. canadensis. As a result, triploids (SHN and SHR), tetraploids (SHRR), pentaploids (SSHHH or SSSHH), hexaploids (SSHHNN, SSHHRR, and SSSHHH), octoploids (SSSSHHHH), and aneuploids, including tetrasomics and trisomics were produced and examined morphologically and cytologically. Somaclones of E. canadensis in which chromosome numbers were not changed were also evaluated morphologically and cytologically in relation to forage improvement. The results are summarized as follows: (1) Sterile allotriploid hybrids with genomes from E. canadensis, P. juncea, and S. cereale were more productive than the parents, accounting for forage yield increases of 8% in SHN hybrids and 64% in SHR hybrids, respectively, compared to the higher-yielding parent, E. canadensis, grown under greenhouse conditions. (2) Allohexaploids with the genome constitutions SSHHNN and SSHHRR showed increased intragenomic bivalent formation and partial fertility. Allohexaploids indicated remote phylogenetic relationships among S, H, and N and among S, H, and R genomes. (3) Induced autoallooctoploids (SSSSHHHH) behaved cytologically like diploids and were fertile. An octoploid regenerant yielded 92% octoploid progeny in the first selfed generation. (4) Vigorous hexaploids with the genome constitutions SSSHHH were derived from intercrosses and backcrosses of octoploids with tetraploids. These hexaploids were found to be useful agronomically and yielded primary aneuploid stocks such as tetrasomics and trisomics for studies of genetics and genome relationships and an understanding of the nature of the genome. (5) Tissue culture was effective in elevating the ploidy level of E. canadensis and also contributed to small changes in chromosome structure. Callus cultures of hybrid embryos and subsequent plant regeneration was used as an alternative to embryo rescue and seemed to overcome hybrid necrosis in the SHR hybrid regenerant. (6) None of the intergeneric hybrids and somaclones of E. canadensis were suitable for direct use as forage germplasm because of poor plant vigor, low seed set, and cytological instability in advanced generations. Some of them would be useful for the production of alien chromosome addition or substitution lines and as aneuploid stocks for genetic studies.