CONICET | Buscador de Institutos y Recursos Humanos

Fertility is a measure of reproductive success, defined as the capacity of an individual to reproduce and generateoffspring, and has been identified as an important trait correlating to the invasive ability of a species.Hymenachne amplexicaulis (Rudge) Nees is a grass native to South America of high bromatological quality,making it a species with good forage potential. In the places where it was introduced it is now considered aninvasive weed due to its dominance over native vegetation. In this work, individuals of H. amplexicaulis wereanalyzed from a native population in its southernmost native range, situated on Yacyretá reservoir dam. Allindividuals show a diploid cytotype with two B chromosomes (2n=2x=20+2B). This is the first chromosomecount recording B chromosomes for the genus, and a new cytotype for the species. The karyotype was found tobe symmetrical and unimodal, composed by 20 metacentric chromosomes and two small B chromosomes. Pollenviability was tested at 90.6%, seed set production of population reaches 18.65%, and the viable seeds presenteda germination power of 41%. The reproductive performance is less than expected with respect to the meanamount of spikelets that a single inflorescence possesses and notwithstanding optimal conditions of supply andavailability of viable pollen for fecundation. Germination test indicate good seed quality and viability in nativerange. In H. amplexicaulis effective fertility is lower than its potential fertility, but it is not an indicator of absenceof invasive threat. Reproductive performance of B host plants indicates sufficient invasive potential.