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Reproduction in Crested Wheatgrass Triploids¹

Triploid Agropyron cristatum (L.) Gaertn. crossed most readily with diploid A. cristatum, 2n = 14, but some crossing also occurred with tetraploid A. desertorum, 2n =r 28; hexaploid A. cristatum, 2n = 42; and an A. repens (L.) Gaertn. x A. cristatum induced-amphiploid hybrid, 2n = 56. Chromosome numbers of 183 progeny ranged from 2n = 14 to 38, with 80% of the progeny having 14, 15, or 16 chromosomes. At least 90% of the progeny of triploid A. cristatum came from reduced 7-, 8-, or 9-chromosome eggs. Triploid A. cristatum is an excellent source of primary trisomics, which can be recognized by aberrant morphology and reduced fertility.

Triploid (A. desertorum (Fisch. ex Link) Schult. crossed most frequently with tetraploid A. desertorum, but it also crossed occasionally with diploid and hexaploid A. cristatum. Chromosome numbers in 59 open-pollination progeny ranged from 2n = 23 to 42. Triploid A. desertorum produced no functional eggs with less than nine chromosomes, and at least half of its functional eggs were unreduced. Chromosome numbers in 57 open-pollination progeny of triploid A. cristatum x A. desertorum ranged from 2n = 24 to 56. More than 75% of the functional eggs of this triploid hybrid were unreduced.

The wide differences in proportion of functional unreduced eggs produced by the three types of triploids were probably due to differential abortion of reduced gametes rather than to basic differences in patterns of megasporogenesis. Each triploid is capable of serving as a genetic bridge between diploid and polyploid crested wheatgrasses; however, gene flow is mostly from diploid to polyploid.

Key Words: Agropyron cristatum • Agropyron desertorum • Polyploidy • Aneuploidy • Trisomics

² Research Geneticist, Plant Science Research Division, Agricultural Research Service, U. S. Department of Agriculture. Logan, Utah 84321.

Received for publication February 11, 1971.