Submitted to: International Grasslands Congress
Publication Type: Proceedings
Publication Acceptance Date: 6/8/1997
Publication Date: N/A
Interpretive Summary: Common dallisgrass is an important forage grass in the southern US because of its excellent forage quality. However, the grass is susceptible to the disease that causes ergot which reduces seed yields and if grazed at the wrong time, can cause ergot poisoning in cattle. The logical way to eliminate this problem is to breed for resistance to the fungus that causes sthe disease. However, the grass reproduces by apomixis, an asexual method of reproduction and essentially all of the common dallisgrass is genetically the same which means all of it is susceptible to ergot. In order to breed for resistance to this disease, sexually reproducing types are needed. Common dallisgrass is a natural hybrid and if the original parents were identified, they could be crossed to produce new forms which could be resistant to ergot. This reports the progress made in identifying the parents of common dallisgrass.
Technical Abstract: Common dallisgrass, Paspalum dilatatum Poir., an important warm-season forage grass, is an obligate apomict with 50 chromosomes which associate as 20 bivalents and 10 univalents during meiosis. Because efforts to improve the grass have not been successful, a phylogenetic investigation was initiated to identify the progenitors of common dallisgrass in an effort to ocircumvent the apomictic barrier to improvement. The genomic composition has been determined for four dallisgrass biotypes: yellow-anthered (2n=4x=40) IIJJ; common (2n=5x=50) IIJJX; Uruguayan (2n=6x=60) IIJJXX; and Uruguaiana (2n=6x=60) IIJJXX1. While the source of the X genome is unknown, the genes controlling apomixis are on at least one of the X chromosomes because biotypes with 10 or more X chromosomes are apomictic. However, when four or five of the X chromosomes are missing, apomixis is not expressed. This suggests that apomixis is controlled by more than one gene and at least one of the X chromosomes must be present for apomixis to be expressed.