Morphology and cytology of the reciprocal hybrids between Elymus trachycaulus and Elymus canadensis

Abstract

Reciprocal hybrids between Elymus trachycaulus (2n = 4x = 28) and Elymus canadensis (2n = 4x = 28) were generated through emasculation and hand-pollination. All the F1 hybrid plants were tetraploids (2n = 28). The F1 hybrids were readily produced (9 plants from 150 pollinated florets; 6% success) in crosses where E. canadensis was used as the pistillate parent and the hybrid plants were produced directly from the apparently normal hybrid seeds. The percentage of hybrid plants produced was lower (7 plants from 400 pollinated florets; 1.7% success) in crosses where E. trachycaulus was used as the pistillate parent, and embryo culture procedures were necessary to recover plants from the shriveled seeds produced. Distinct morphological as well as cytological differences between the reciprocal hybrids were observed. All the F1 plants from each reciprocal cross more closely resembled their pistillate parent, indicating a strong maternal influence. Chromosome pairing at metaphase I showed a very high frequency of cells with a hexavalent configuration (69–81%) and a low frequency of cells with univalents (15–23%) in hybrids produced from crosses with E. canadensis as the pistillate parent. In all hybrids produced from crosses with E. trachycaulus as the pistillate parent, chromosome pairing showed a relatively low frequency of cells with a hexavalent (12–22%), while the frequency of cells with univalents was high (78–81%). Cytology of these hybrids indicates substantial control by cytoplasmic genes on chromosome pairing behavior. Reciprocal hybridization betwen octaploid E. trachycaulus (8x) and tetraploid E. canadensis (4x) plants yielded three 2n = 42, one 2n = 41, and one 2n = 39 hybrid plants. All plants were weak and sterile and more closely resembled the octaploid parent, although some intermediate characters were apparent.Key words: Elymus, reciprocal hybrids, maternal influence, cytoplasmic genes, chromosome pairing.