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Effects of Geographic Origin and Seed Production Environments on Apomixis in Kentucky Bluegrass¹

The objectives were to determine whether the frequency of atypical aberrant plants of Kentucky bluegrass (Poa pratensis L.) was affected by geographic origin of genotypes and by seed production environments. An increase in frequency of aberrants may adversely affect seed certification of production fields established outside the area of geographic origin of apomictic cultivars. Seed was produced in seven states for open-pollinated progeny tests of highly apomictic and diverse clones. Progenies were grown at Beltsville, Md., and near State College, Pa. Plants of each progeny were classified as typical apomictic, aberrant, or weak. The frequency of aberrant plus weak plants (13.6%) was higher at locations (Alabama and Kentucky) with wide overall anthesis range (at least 4 weeks) and short photoperiod than the frequency (7.2%) at locations (Maryland, New Hampshire, and Vermont) with narrow anthesis range (6 to 9 days) and long photoperiod (> 14.5 hours). The frequency of aberrant and weak plants was considerably higher for four clones (13.6%) than for the remaining five (5.0%). Clones with high frequency of aberrants traced to widely diverse origin. The results indicate that the frequency of aberrant progeny of Kentucky bluegrass is not adversely affected when seed is produced outside the area of geographic origin of a cultivar.

Seed produced on 40 plants scored as weak was used to ascertain whether weak plants were typical or aberrant. Only two plants produced typical progeny; the remaining 38 produced segregating apomictic or sexual progenies. Although most weak plants were aberrant and would probably not become established under competitive conditions with typical apomictic progeny, aberrant and weak plants should be rogued from space-planted fields that are used for the production of breeder seed.

Cytological examination of megasporogenesis was inconclusive in regards to the hypothesis that environments influence the initiation of aposporous nucellar cells. Examination of embryo development failed to distinguish possible effects of either genotype or environment on relative frequency of apomictic and sexual reproduction of ovules.

Key Words: Apospory • Facultative apomixis • Seed certification • Poa pratensis L.

² Former research agronomist, USDA-ARS (presently professor, Dep. of Agronomy and Plant Genetics, Univ. of Minnesota, St. Paul, MN 55108); research geneticist, USDA-ARS, U.S. Regional Pasture Research Lab., University Park, PA 16802; research geneticist, USDA-ARS, Texas A&M Univ., College Station, TX 77843; research agronomist, USDA-ARS, Univ. of Kentucky, Lexington, KY 40506; research geneticist, USDA-ARS, Utah State Univ., Logan, UT 84322; professor, Univ. of New Hampshire, Durham, NH 03824; professor, Auburn Univ. Auburn, AL 36830; research agronomist, USDA-ARS, Irrigated Agriculture Research & Extension Center, Prosser, WA 99350; associate professor, Univ. of Vermont, Burlington, VT 05401.

Received for publication February 7, 1976.