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Inbreeding Depression in Diploid, Tetraploid, and Hexaploid Crested Wheatgrass¹

The effects of inbreeding on vegetative vigor and fertility were evaluated on 2 diploid, 164 tetraploid, and 30 hexaploid S₁'s progenies of crested wheatgrass represented by 252, 13,770, and 1,543 plants, respectively. Forage yields of S₁ progenies averaged 64.1, 49.6, and 32.6% of comparable O.P. progeny yields in the diploid, tetraploid, and hexaploid populations, respectively. Open-fertility of diploid, tetraploid, and hexaploid S₁ progenies averaged 47.8, 57.9, and 31.0%, respectively, of that of their O.P. counterparts. Mean self-fertility of S₁ diploids and tetraploids was not reduced by one generation of selling; however, self-fertility of hexaploid S₁s was 23.1% of that of the O.P. plants. The effect of inbreeding on forage yield and self- and open-fertility was highly variable from progeny to progeny within each population. The tetraploid and hexaploid populations suffered much greater inbreeding depression than was expected on the basis of the theoretical approach to homozygosity associated with selling in autoploids. The severe inbreeding depression of the tetraploid and hexaploid populations was attributed to chromosome abberations that accumulate in species buffered by autoploidy. Relatively self-fertile progenies were found at each ploidy level. The most self-fertile diploid, tetraploid, and hexaploid progenies averaged 5.0, 22.3, and 29.6 self seeds per spike, respectively. Self-fertile populations of diploid, tetraploid, and hexaploid crested wheatgrass can apparently be obtained by simple selection procedures.

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

Received for publication September 4, 1965.