| Determination of species relationships in the genus
Agropyron by interspecific hybridization and genome analysis 1)
J. SCHULZ-SCHAEFFER and P. W. ALLDERDICE Department of Plant and Soil Science, and Genetics Institute Montana State University, Bozeman, Montana, U.S.A. Cytogenetic study of 6 interspecific Agropyron hybrids has provided further evidence for the world-wide distribution of genomes which seem to have common ancestry with the spicatum (S) genome. Modifications of the S genome were shown to be present in plants of 10 strains of 8 Agropyron species which are listed along with their accession numbers and seed sources in Table 1. Hybrids established and studied were: A. subsecundum x A. latiglume, A. caninum x A. latiglume, A. arizonicum x A. caninum, A. caninum x A. riparium, A. brachyphyllum x A. riparium and A. semicostatum x A. trachycaulum. Each of these hybrids were sterile with the exception of A. caninum x A. latiglume which was highly fertile. Parent and hybrid plants were analyzed morphologically and cytologically. The average chromosome associations for the six newly established interspecific hybrids are listed in Table 2. New genome formulas for A. arizonicum, A. brachyphyllum, A. caninum, A. latiglume, A. riparium, A. semicostatum (2n=28), A. semicostatum (2n=42), A. subsecundum and A. trachycaulum are proposed in Table 3 and compared with already published formulas. These formulas are based on evidence shown in Table 2, from evidence of earlier published hybridization results, and from earlier cytologicai and serological results obtained in the Montana laboratory. In 5 of the 6 hybrids, bivalent pairing ranged from 10.13 in A. arizonicum x A. caninum to 12.15 in A. subsecundum x A. latiglume. These data suggest close homologies of two basic genomes which were designated S and B (Table 3). Some authors have designated genome S with the letter A. But since a definite relationship has been established between this basic genome and the chromosomes of diploid A.spicatum, we prefer to call it S. The second basic genome B was assumed to be different from genome S in earlier studies because tetraploid species in this group do not form quadrivalents in meiosis (for instance BOYLE 1963). We are not completely satisfied with this argument since genetic control of meiosis can lead to meiotic diploidy in autotetraploids with complete bivalent pairing and lack of quadrivalents. Only the discovery of a diploid which carries the B genome would completely answer the question of its origin. Since this diploid ancestor may not exist anymore, other biosystematic methods may help to clarify the true nature of ploidy in these tetraploids. However, we provisionally accept the present concept of alloploidy. |
| 1) These investigations were supported by the National Science Foundation,
Grants NSF-G19363 and NSF-GB-2714. Contribution of the Montana Agricultural Experiment Station, Bozeman. Paper No.725, Journal Series, Montana Agricultural Experiment Station. Published with approval of director. |
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