Several aspects related to the reproductive biology of the valuable Argentinian native forage grass Bromus athletics were studied in three populations to identify its reproductive system and the factors that limit its reproductive success. In vitro pollen, fertility and germinability were measured, and the behavior of pollen tubes under self-pollination was compared with that of cross-pollen. Fruit set under different pollination conditions was also determined. Pollen amount and pollen fertility do not per se limit fruit set, and pollen fertility was not impaired by bagging; however, in vitro pollen germination was low (22.5%) which may limit reproduction. The differential behavior of pollen tubes under selfing and crossing, as well as the high pollen: ovule ratio, indicate allogamy. Substantial fruit set (38.3%) occurred only when stigmas received non-self pollen in adequate amounts. Treatments providing only self-or no pollination drastically reduced or suppressed fruit set, which suggests lack of apomixis and, at the same time, the operation of a self-incompatibility mechanism. The limited reproductive success of a natural population of this species may be the consequence of self-incompatibility coupled with reduced genetic variation for incompatibility alleles.
