Defining breeding techniques based on reproductive modes: the cases of Acroceras macrum and Paspalum simplex

CARLOS A. ACUÑA

Buenos Aires

Simposio; 5th International Symposium of Forage Breeding; 2015

Warm-season grasses are highly diverse in terms of modes of reproduction. Most cultivated forage grasses have been well characterized for their reproductive modes, and breeding has been successful for many of them. However, there are many cultivated and non-cultivated species with potential as forages that have been only partially characterized and their genetic improvement are limited. Acroceras macrum Stapf is a clonally-propagated species native from Africa, which is cultivated in areas with waterlogged soils around the world. Little was known about the species mode of reproduction. Renewed interest on this species has driven a genetic characterization between 2010 and 2014. The species is an allopolyploid, and the predominant ploidy levels are the tetraploid and hexaploid with a base chromosome number of x=9. A. macrum reproduces sexually and behaves as cross-pollinated due to self-incompatibility. Pollen viability, and seed set are medium to low in comparison with other cultivated polyploid grasses. Breeding techniques developed for allogamous species are expected to be adequate for A. macrum. Paspalum simplex Morong is a non-cultivated species native from South America, which has been identified by beef cattle producer as one of the more productive components of local rangelands. An intensive genetic characterization of this species has been accomplished during the last 15 years. The species has a base chromosome number of x=10, and diploid, triploid, tetraploid and hexaploid types were identified. However, the tetraploid populations predominate. The diploid reproduces sexually and behaves as cross-pollinated while the polyploids are aposporous-apomictic. A recent population study indicated that the maximum diversity is present within diploid populations and among tetraploid ones. Apomixis segregates as a dominant Mendelian trait with a distortion against the apomictic hybrids. Phenotypic recurrent selection is expected to be adequate for the diploid type. Ecotype selection and fixation of superior hybrids by apomixis are recommended for the tetraploid type.