Comparative Mapping of Growth Habit, Plant Height, and Flowering QTLs in Two Interspecific Families of Leymus

Leymus cinereus (Scribn. & Merr.) A´ .L ove and L. triticoides (Buckley) Pilg. are tall caespitose and short rhizomatous perennial Triticeae grasses, respectively. Circumference of rhizome spreading, proportion of bolting culms, anthesis date, and plant height were eval- uated in two mapping families derived from two interspecific hybrids of L. cinereus Acc:636 and L. triticoides Acc:641 accessions, backcrossed to one L. triticoides tester. Two circumference, two bolting, and two height QTLs were homologous between families. Two circumference, seven bolting, all five anthesis date, and five height QTLs were family specific. Thus, substantial QTL variation was apparent within and be- tween natural source populations of these species. Two of the four circumference QTLs were detected in homoeologous regions of linkage groups 3a and 3b in both families, indicating that one gene may control much of the dramatic difference in growth habit between these species. A major height QTL detected in both families may correspond with dwarfing mutations on barley 2H and wheat 2A. The L. cinereus parent contributed negative alleles for all four circumference QTLs, five of nine bolting QTLs, two of five anthesis date QTLs, and one of seven height QTLs. Coupling of synergistic QTL allele effects within parental species was consistent with the divergent growth habit and plant height of L. cinereus and L. triticoides. Conversely, antagonistic QTL alleles evidently caused transgressive segregation in reproductive bolting and flowering time. L EYMUS wildryes are long-lived Triticeae grasses, closely related to wheat (Triticum spp.) and barley (Hordeum vulgare L.). The genus Leymus includes about 30 species distributed throughout temperate re- gions of Europe, Asia, and the Americas (Dewey, 1984). More than half of all Leymus species are allotetraploids (2n 5 4x 5 28), but octoploid (2n 5 8x 5 56) and do- decaploid (2n 5 12x 5 84) variants may arise from inter- specific hybrids (Anamthawat-Jonsson and Bodvarsdottir, 2001) or autoduplication within species. These cool- season grasses display remarkable variation in growth habit and stature with unusual adaptation to harsh polar, desert, saline, and erosion-prone environments. Leymus triticoides (creeping or beardless wildrye) and L. cinereus (basin wildrye) are closely related but mor- phologically divergent North American range grasses. Aggressive rhizomes and adaptation to poorly drained alkaline sites, primarily within the western USA, charac- terize sod-forming L. triticoides (0.3-0.7 m). Conversely, L. cinereus is a tall (up to 2 m) conspicuous bunchgrass adapted to deep well-drained soils from Saskatchewan to British Columbia, south to California, northern Arizona, and New Mexico, and east to South Dakota and Minne- sota. Mostpopulationsof L. cinereus andL. triticoidesare allotetraploids; however, octoploid forms of L. cinereus are typical in the Pacific Northwest. Basin wildrye, and octoploid giant wildrye (L. condensatus (J. Presl) A ´ . Love), are the largest cool-season bunch grasses native to western North America. Artificial hybrids of L. cinereus, L. triticoides,and otherNorthAmericanLeymus wildryes