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Cytological Studies of Four Diploid Dactylis Subspecies, Their Hybrids and Induced Tetraploid Hybrids¹

To assess subspecies relationships within Dactylis glomerata L., chiasma frequencies and chromosome pairing of four diploids and their diploid and tetraploid hybrids were studied. Subspecies himalayensis, ibizensis, juncinella, and Smithii were chosen because of their extreme morphological, geographical, and ecological discontinuities. Pairing in parents and hybrids was generally normal and coincided with expected or published frequencies. Ssp. Smithii had more univalents and fewer chiasma than other parents. Chiasma frequencies of the diploid hybrids himalayensis x juncinella, juncinella x Smithii, and himalayensis x Smithii were lower than those of the corresponding tetraploid hybrids. Chromosome structural differences, although minor, are most pronounced between ssp. juncinella and ssp. Smithii, and slightly less between ssp. Smithii and ssp. himalayensis. Ssp. ibizensis is the least structurally differentiated from the others and is probably the relict of a larger gene pool through which genetic exchange had previously occurred with the other subspecies or their ancestral forms.

Key Words: Chiasma frequencies • Chromosome pairing • Subspecies relationships

² Research Assistant and Professor, Department of Crop Science, North Carolina State University.

Received for publication July 3, 1970.