Apomixis importance for tropical forage grass selection and breeding. Review

Apomixis is a reproductive system resulting in seed production without gametes fusion, and produces, through generations. offspring that is a genetic copy from the maternal progenitor. Apomixis importance is widespread among tropical grasses: Bothriochloa, Bouteloua, Brachiaria, Cablipedium, Cenchrus, Dichanthium, Eragrostis, Hyparrhema, Melinis, Panicum, Paspalum, Pennisetum, Setaria, Tripsacum. Urochloa, among the most important. Apomictic species contain diploid as well as polyploid individuals conforming "agamic complexes" and reproductive barriers limited both by apomixis as well as ploidy level which has a great impact on apomictic species utilization. Diploid individuals maintain active the sexuality and these are rare out of the center of specie's genetic origin center. Polyploid individuals in nature are apomictic, and sexual individuals may be induced to polyploidy in the laboratory, allowing hybrid descendants production. Genetic richness originated within the specie's center of diversity is the basis to overcome productive challenges and ecological stability: dry season productivity, nitrogen fixation, forage quality, pest and disease resistance, etc.; as it has been shown by successful breeding programs for Brachiaria and Panicum, between the most recognized for Latin America, and Cenchrus in USA. Apomixis research advancements has elucidated the biology for this reproductive process as well as the techniques for its manipulation; however, the impact of this advancements on forage research in Mexico has promoted a critical review on forage genetic resources utilization, resulting in an increased interest on hybrid material production to face the requirements for extensive grazing production systems in Mexico.