CYTOGENETICS OF AGROPYRON FERGANENSE AND ITS HYBRIDS WITH SIX SPECIES OF AGROPYRON, ELYMUS, AND SITANION

Meiosis and mode of reproduction are described in Agropyronferganense Drob., a perennial forage grass from Central Asia. This species is diploid (2n = 14); it exhibits normal meiosis and reproduces by cross-pollination. Hybrids were produced between A. ferganense and six species with known genome formulas: 1) North American A. spicatum (Pursh) Scribn. & Smith, an SS diploid (2n = 14), 2) Middle Eastern A. libanoticum Hack., an SS diploid (2n = 14), 3) North American A. dasystachyum (Hook.) Scribn., an SSHH tetraploid (2n = 28), 4) Eurasian A. caninum (L.) Beauv., an SSHH tetraploid (2n = 28), 5) North American Sitation hystrix (Nutt.) J. G. Smith, an SSHH tetraploid (2n = 28), and 6) South American Elymus patagonicus Speg., an SSHHHH hexaploid (2n = 42). Almost complete chromosome pairing in the A. ferganense x A. spicatum and A. libanoticum hybrids demonstrated that A. fergenanse is an SS diploid, but it is genetically isolated from the other SS diploids because of high sterility in the F1 hybrids. S-genome diploids form a network of species that extend from the Middle East through Central Asia to western North America. Frequent occurrence of seven univalents and seven bivalents at metaphase I in the triploid hybrids of A. ferganense x A. dasystachyum, A. caninum and S. hystrix was consistent with the proposed genome formulas of SS for A. ferganense, SSHH for the three tetraploid species, and SSH for the hybrids. Chromosome pairing was highly variable in the A. ferganense x E. patagonicus hybrids; however, some cells had almost complete bivalent pairing, an expected observation in an SSHH hybrid from a cross between an SS diploid (A. ferganense) and an SSHHHH hexaploid (E. patagonicus). Various options were considered concerning the appropriate generic classification of the S-genome diploids, which are now commonly placed in Agropyron. The inclusion of these species in the genus Elytrigia, as advocated by some Soviet taxonomists, appears to be a reasonable decision. AGROPYRON FERGANENSE Drob. is a perennial, caespitose forage grass that grows on stony slopes in the Pamir and Alai mountain ranges of Central Asia (Nevski, 1934). The cytogenetic and reproductive characteristics of this grass have not been described. Previous absence of interspecific and intergeneric hybrids involving A. ferganense has precluded the study of genomic and phylogenetic relationships with other species. Seed of A. ferganense first came into my possession in 1973. Since then, A. ferganense has been hybridized with several other perennial Triticeae species including Agropyron spicatum (Pursh) Scribn. & Smith, A. libanoticum Hack., A. dasystachyum (Hook.) Scribn., A. caninum (L.) Beauv., Sitanion hystrix (Nutt.) J. G. Smith, and Elymus patagonicus I Received for publication 17 January 1980; revision accepted 27 February 1980. Cooperative investigations of the USDA-SEA-AR and the Utah Agricultural Experiment Station, Logan, Utah. Approved as Journal Paper No. 2514. I am indebted to Mrs. C. T. Hsiao who made most of the cytological analyses. Speg. The six species with which A. ferganense was hybridized have known genomic constitutions; consequently, they can be used as "tester" stocks to determine the genomic constitution of A. ferganense. Agropyron spicatum and A. libanoticum are diploids (2n = 14) from North America and the Middle East, respectively. Both diploids carry the basic S genome (Stebbins and Snyder, 1956; Dewey, 1969). Eurasian A. caninum, North American A. dasystachyum, and North American S. hystrix are allotetraploids (2n = 28) with the same basic genome formula, SSHH (Dewey, 1971). Elymus patagonicus, a South American species, is a segmental autoallohexaploid (2n = 42) that has been represented genomically as SSH1 H, H2H2 (Dewey, 1972). The purposes of this study were to describe the reproductive and cytogenetic characteristics of A. ferganense and to determine its genomic relationships with other species of the Triticeae tribe. This study is part of a longterm and continuing effort to define the biological and phylogenetic relationships among