Natural hybrids of Elymus elymoides x Leymus salinus subsp. salmonis (Poaceae: Triticeae)

Several putative hybrids between Elymus elymoides (Rafin.) Sweezey and Leymus salinus (M.E. Jones) A. Love subsp. salmonis (C. Hitchc.) Atkins were found growing on the west side of the Great Salt Lake, near Lakeside, UT in 1995. Naturally occurring hybrids between these two species have not been documented previously. Cytological, morphological, and chloroplast DNA analysis of the hybrids and parents confirmed the hypothesis that these plants were hybrids of the two species. Elymus elymoides and L. salinus subsp. salmonis were the only Triticeae species growing in the area that could have contributed to the intermediate morphological features expressed in the hybrids. Leymus salinus subsp. salmonis (NsNsXmXm; 2n = 4x = 28) and E. elymoides (StStHH; 2n = 4x = 28) are allotetraploids that regularly formed 14 bivalents at metaphase I (MI). The hybrids between the two species are also tetraploids and averaged 22.1 univalents and 2.86 bivalent associations per cell at MI. Chromosome pairing in the hybrids suggests essentially no homology between the chromosomes from the two parents; thus the genomic formula for the hybrid can be written as StHNsXm. The hybrids were morphologically intermediate between the suspected parent species, but they resembled L. salinus subsp. salmonis more closely than E. elymoides. Analysis of chloroplast DNA in the hybrid and its putative parents, demonstrates cytoplasmic DNA identical to E. elymoides, suggesting that E. elymoides was the maternal parent. Complete sterility and reduction in chromosome pairing in the natural hybrids between E. elymoides and L. salinus subsp. salmonis suggest that the potential for genetic exchange between the two species is limited or lacking. Due to hybrid sterility, the natural hybrid will have little impact on the native vegetation of the western deserts of Utah and, without restored fertility, has no potential as a restoration grass on semiarid range sites.