Reproductive biology of Setaria magna Griseb. (Poaceae: Panicoideae: Paniceae)

The genus Setaria is economically important because many species are cultivated for grains or forage. Setaria magna is an American species, native to North America and introduced in South America. The morphological aspect of this species is similar to S. italica (foxtail millet), suggesting its potential value as a crop. The purpose of this work was to understand the breeding system (selfpollination vs. open pollination) of S. magna; additionally, the floral development was described. The results of the breeding system analysis indicated that S. magna is mainly autogamous and does not appear to have a self-incompatibility mechanism. The floral development observed was similar to that described for other Paniceae; in most of the spikelets only the upper anthecium developed fruit, but a small number of spikelets presented bisexual lower florets. These spikelets produced two caryopses per spikelet. Thus, S. magna can produced two types of dispersal units; a few whitish naked caryopses from the lower anthecium that fall without their lemma and palea at maturity; and a high number of brown caryopses protected by the lemma and palea from the upper anthecium. The presence of a normal embryo sac in the upper anthecium suggests that S. magna would present normal sexual reproduction, although we can not reject the formation of apomitic seeds in the lower anthecium.