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United States Department of Agriculture

Agricultural Research Service

Title: Apomixis and Sexuality in Some Paspalum Species

Author
item Burson, Byron

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 3, 1997
Publication Date: N/A

Interpretive Summary: During the past several years a number of new grasses have been introduced into the USDA-ARS National Plant Germplasm System from other countries. Little is known about them and they need to be evaluated and characterized for various traits before they can be used in plant improvement programs. Fourteen grasses belonging to eight different species, all of which are related to both bahiagrass and dallisgrass, were investigated to determine their chromosome number and how they reproduce. These grasses have traits that could be used to improve existing forage grasses; therefore, any information regarding their cytology and reproductive behavior is essential in using these plants in a breeding program. Plants of four species were diploids with 20 chromosomes and they were sexual. Ten plants had 40 chromosomes and were facultative apomicts. A facultative apomict reproduces by both sexual and apomictic means. Apomixis is an asexual or vegetative form of reproduction where seed are produced without fertilization. One plant had 50 chromosomes and it reproduced only by apomixis. The chromosome numbers for 10 of the plants were new for those species and the method of reproduction had never been determined for 13 of the plants. These findings provide new fundamental information for these grasses and also information how the species can be correctly used in a breeding program to provide a substantial savings in labor and materials

Technical Abstract: Paspalum is a large genus of grasses of which several are important forage and turf grasses. Little or no information is available concerning the cytology and reproductive behavior of many of the species. The objectives of this study were to determine the method of reproduction, cytology and fertility of accessions of several different Paspalum species in the National Plant Germplasm Systems. Paspalum modestum, P. monostychyum, P. repens and one P. alcalinum accession were sexual diploids with 2n=2x=20 chromosomes. Meiosis was regular with primarily bivalent pairing. Even though P. Modestum was sexual, the female gametophyte deteriorated in 43% of the ovules. Two P. alcalinum, one P. falcatum, two P. paucifolium, three P. polyphyllum and P. unispicatum accessions were tetraploids with 2n=4x=40 chromosomes. During meiosis their chromosomes associated primarily as bivalents, quadrivalents, and univalents. Regardless of the species, all tetraploids were facultative aposporous apomicts. One P. alcalinum accession was a pentaploid with 50 chromosomes. Meiosis was irregular with the chromosomes associating as univalents, bivalents, trivalents and quadrivalents. This accession reproduced as an obligate aposporous apomict. Seed set in P. modestum and P. monostychyum was very low but was high enough in the other species that they could be propagated by seed. These findings demonstrate the reproductive and cytological diversity within this large complex genus

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