Apomixis for Cultivar Development in Tropical Forage Grasses

Abstract

Apomixis—asexual reproduction through seed—provides a convenient means to faithfully propagate even heterozygous genotypes and hence exploit heterosis, in several naturally apomictic, warm‐season forage grasses. Inheritance of apomixis has been shown to be monogenic dominant in at least four economically important panacoid grasses. Previously proposed breeding schemes for apomicts do not provide a means to accumulate genes contributing to nonadditive, heterotic effects over cycles of selection and recombination. Following the development of successful brachiariagrass [Brachiaria (Trin.) Griseb] cultivars by ecotype selection, artificial hybridization of brachiariagrasses began in the late 1980s with the development of a sexual tetraploidized biotype of the natural diploid, sexual ruzigrass (Brachiaria ruziziensis Germain and Evrard). A breeding scheme—recurrent selection for specific combining ability—designed to accumulate nonadditive effects, originally proposed for sexual maize (Zea mays L.), is suggested as an appropriate scheme for improvement of apomictic tropical grasses. Recurrent selection on specific combining ability or interpopulation selection schemes such as reciprocal recurrent selection should be appropriate for other asexually propagated crops.

Independence of Resistance in Brachiaria spp. to Nymphs or to Adult Spittlebugs (Hemiptera: Cercopidae): Implications for Breeding for Resistance

“…In 2005, 2,250 brachiariagrass hybrids were formed by pollinating 223 tetraploid sexual clones with a common pollen parent (Miles 2007). The sexual maternal clones were taken from a synthetic sexual tetraploid brachiariagrass breeding population that had undergone Þve cycles of recurrent intrapopulation selection, with major selection pressure on antibiotic resistance to spittlebug nymphs (Miles et al 2006).…”

Estimate of genetic parameters in Brachiaria decumbens hybrids

“…In RS, a sexually reproducing breeding population can be selected based on the performance of the hybrid progenies formed by crosses of each of a series of sexual clones with a single apomictic tester genotype (Miles 2007). A population of 1,415 intraspecific hybrids of B. decumbens was obtained at Embrapa Beef Cattle Center by crossing 75 sexual hybrids from the base population of B. decumbens with cv.…”

Diversity in Apomictic Populations of Paspalum simplex Morong

“…Among them, Brachiaria decumbens, B. brizanta, Cenchrus ciliaris, Panicum maximum, Paspalum dilatatum, and P. notatum are extensively cultivated around the world (Skerman and Riveros, 1994). Although different breeding techniques have been developed for the genetic improvement of apomictic species (Hanna, 1995;Vogel and Burson, 2004;Miles, 2007), most commercially available cultivars have been the result of direct selection of natural variants collected at different locations (Vogel and Burson, 2004;Blount and Acuña, 2009). These ecotypes are evaluated in the target environment and the superior ones are released as cultivars.…”