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Reproduction and breeding in a dioecious bluegrass, Poa confinis Vasey Hanna, Michael Ross

Abstract

Dune bluegrass, Poa confinis Vasey, is a dioecious grass native to the Pacific Coast of North America. It has a very restricted habitat, being confined almost entirely to the semi-stabilized, porous sand areas of the coast. Herbarium studies, and first-hand observations of a number of P. confinis sites indicate that it is a very uniform species. Under cultivation on The University of British Columbia farm P. confinis grows vigorously and forms a thick sod. Its fine-leaved growth, rhizomatous root system and rapidly-spreading habit, together with the sandy nature of its native habitat, all suggest that it may find use as a turf species for sandy golf courses and similar areas along the coast. A survey of the literature on reproduction in the bluegrasses reveals that apomixis is widespread in Poa, and that apospory or diplospory followed by pseudo-gamous embryo development is the usual form of apomictic reproduction. Breeding procedures with apomictic blue-grasses muct be considerably modified, but the standard techniques of improvement are still theoretically available to the bluegrass breeder. A cytological study of embryo sac development in pistillate plants indicates that it follows the "normal scheme, and that reproduction is sexual. Each ovule contains a single EMC which undergoes a regular meiotic division, giving rise to a triad or tetrad of megaspores, one of which forms the haploid embryo sac. Somatic chromosome numbers of 2n = 42 are found in two EMCs in diakinesis. The presence of twin embryo sacs is observed in two ovules Very marked antipodal development, with an increase in size and number of cells, and in the number of nuclei per cell, is characteristic of the mature female gametophyte. Microsporogenesis in the staminate plants also appears "normal”. Studies of anthers in pistillate floret and ovules in staminate florets show that their development proceeds normally up to a certain point and then breaks down. Embryo and endosperm development can be seen in sections of ovules prepared after the pollination of P. confinis by P. pratensis. The embryos are believed to be the product of true hybridization. Seed forms after all the crossings among P. confinis, P. macrantha, P. pratensis and P. compressa using the first two species as female parents, but the seed invariably shrivels shortly before reaching maturity. The excision of hybrid embryos from seeds formed after some of the interspecific crosses, and the culture of these embryos on agar media have been successfully carried out. Tissues of putative macrantha x confinis hybrids are growing, and showing some differentiation. The results indicate that hybrids between P. confinis and other blue grasses can probably be obtained through embryo culture techniques.

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