Hybrids and Induced Amphiploids of Agropyron dasystachyum x Agropyron caninum

Abstract

North American Agropyron dasystachyum (Hook.) Scribn., 2n = 28, and Eurasian A. caninum (L.) Beauv., 2n = 28, hybridized readily and gave rise to vigorous F1 hybrids morphologically intermediate between the parent species. The hybrids formed 14 bivalents in 89 of 225 metaphase-I cells and averaged 1.61I, 13.10II, 0.03III, and 0.03IV per cell. Although A. dasystachyum and A. caninum are morphologically, ecologically, and geographically separated, they contain the same basic genomes, SSXX. Fifty-seven F1's produced 5%-25% stainable pollen and yielded two to more than 600 seeds when open-pollinated. Most progeny were self-fertile, and fertility and meiotic regularity increased in advanced generations. Geographic separation appears to be the only major barrier to extensive introgression between the two species. Chromosome complements of four F1 hybrids were doubled with colchicine, and amphiploid sectors were isolated by repeated vegetative separations of mixoploid clones. The induced amphiploids, 2n=56, averaged 2.74I, 16.88II, 1 31III, and 3.89IV in 45 metaphase I cells. Some irregularity occurred in at least half of the cells at all meiotic stages, and the amphiploids were approximately 50% fertile. Considerable meiotic irregularity and reduced fertility persisted in the subsequent amphiploid generations, although some plants were highly fertile. The plant breeding potential of A. dasystachyum x A. caninum hybrid derivatives is enhanced by their vigor and resistance to the Banks grass mite, Oligonychus pratensis Banks. A multiple breeding approach consisting of: (a) transfer of selected traits from one species to the other; (b) synthesis of tetraploid "microspecies"; and (c) selection among induced amphiploids is suggested to grass breeders.