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Inbreeding Depression in Diploid and Induced-Autotetraploid Crested Wheatgrass¹

Forage and seed yields of diploid crested wheatgrass, Agropyron cristatum (L.) Gaertu., were reduced sharply by selling. Some progenies were much more sensitive to selfing than others. Vigor and fertility reductions averaged 44.9 and 43.4%, respectively, in 15 S₁ progenies. Inbreeding depression of induced-autotetraploid crested wheatgrass was much less than that of comparable diploids. Forage yields of seven induced-tetraploid S₁ progenies declined 17.3%, compared with a 54.9% reduction for their exact diploid counterparts.

Possible causes of rapid loss of vigor in natural autotetraploids are discussed. Newly synthesized autotetraploids—includiug crested wheatgrass; corn, Zea mays L.; Italian ryegrass, Lolium multillorum Lam.; and alsike clover, Trifolium hybridnm L.—show a much lower degree of inbreeding depression than old natural autotetraploids such as alfalfa, Medicago sativa L.; orchardgrass, Dactylis glomerata L.; and crested wheatgrass, Agropyron desertorum (Fisch. ex. Link) Schult. An accumulation of chromosome aberrations and unfavorable gene combinations in species buffered by autoploidy is offered as a major cause of excessive inbreeding depression in natural autotctraploids. The degree of inbreeding depression in natural autotetraploid species may give an indication of their relative ages.

Key Words: Agropyron cristatum • Agropyron desertorum • Polyploidy • Autopolyploidy • Selling

² Research Geneticist. Crops Research Division, ARS, USDA.

Received for publication March 3, 1969.

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