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Facultative Apomixis in Eragrostis curvula¹

Previous reports indicate that weeping lovegrass, [Eragrostis curvula (Schrad.) Nees], reproduces either sexually or by obligate apomixis (diplospory). Recent studies have shown that certain plants of this species are facultative apomicts. Our research objective was to determine the cytological basis for facultative apomixis in weeping lovegrass and to relate reproductive cytology to performance of progeny from lovegrass parents and hybrids. We observed enlarged or late megaspore mother cells (MMC), as determined by integument size, in apomictic strains. Development from these MMCs occurred in either of two ways: 1) direct formation of the embryo sac (diplospory), or 2) delayed meiosis resulting in the formation of a linear tetrad. Progeny tests of plants with both types of reproductive cytology suggests that these patterns indicate facultative apomixis. We did not observe late, greatly enlarged megaspore mother cells or delayed meiosis in sexual plants. Hybrids between sexual plants and highly apomictic common weeping lovegrass were observed to reproduce either sexually or by facultative apomixis. Sexual plants, when self-pollinated, produced no apomictic offspring. Therefore, we concluded that the sexual plants studied probably lack all the necessary genes for expression of apomixis. The uniformity observed in most experimental lines, the low level of sexuality in some apomictic hybrids, and the reduced vigor of many of the aberrant plants suggest that varietal development and maintenance in E. curvula should not be hindered too greatly by facultative apomixis.

Key Words: Diplospory • Megasporogenesis • Embryo sac development • Inheritance of apomixis

² Research geneticists, ARS-USDA, Grassland-Forage Res. Center, Temple, TX 76501, and Dep. of Soil and Crop Sci., Texas A&M Univ., College Station, TX 77843.

Received for publication April 1, 1976.