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Facultative Apomixis in Buffelgrass¹

We studied embryo sac morphology, chromosome number, reproductive behavior, and phenotype of buffelgrass (Cenchrus ciliaris L.) line 18-35 to obtain further evidence regarding the occurrence of facultative apomixis in the species. Line 18-35 is an F₁ llne derived from a cross of obligately sexual TAM-CRD B-Is with an apomictic plant from Africa. Within line 18-35, pistils with single sexual embryo sacs of the Polygonum type occurred at a low frequency in the same inflorescences a~ pistils with aposporous apomictic embryo sacs of the Oenothera type. Some pistils contained a sexual sac and one or more aposporous sacs. A sample of 2,057 pistils from three field plantings and one greenhouse planting had 85.8% apomictic pistils, 5.8% sexual pistils, and 8.4% mixed pistils. Frequency of sexual pistils differed between sampling dates of one field, indicating that environment may have influenced embryo sac type.

In a spaced planting of 1,292 open-pollinated progeny of 18-35, 1,252 progeny resembled the maternal parent, and 40 progeny were offtype. Line 18-35 and 21 of the offtype progeny were tetraploid (2n = 36). Four of these offtype tetraplold progeny produced primarily or exclusively sexual pistils. The 21 offtype tetraplold progeny probably originated by fertilization of reduced eggs. Fifteen offtype progeny were hexaploid and were believed to originate by fertilization of unreduced eggs. We concluded that line 18-35 is facultatively apomictic.

Key Words: Sexual reproduction • Asexual reproduction • Apospory

² Research plant pathologist, U. S. Regional Pasture Research Laboratory, USDA-SEA and former research associate, The Pennsylvania State Univ. (now research geneticist, USDA-SEA, Grassland Soil and Water Research Laboratory, Temple, TX 76501) Univ. Park, PA 16802; and research geneticist USDA-SEA, Texas A&M Univ., College Station, TX 77843.

³ Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by USDA and does not imply its approval to the exclusion of other products that may also be suitable.

Received for publication October 15, 1979.

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