Self-compatibility in modern hybrids of sunflower (Helianthus annuus L.) fruit set in open and self-pollinated (bag isolated) plants grown in two different locations

The increase in sunflower yield due to the active participation of honey bees (Apis melifera L.) in crop pollination has been demonstrated in previous studies. However, this fact is more evident in earlier commercial hybrids. There are reports that suggest that bees are not required in modern commercial hybrids where a high level of self-compatibility occurs. The purpose of this study was to define formation capacity of fully developed fruits (FDF) and incompletely developed fruits (IDF) in two modern sunflower hybrids exposed to open and closed pollination.Two hybrids, one of half cycle and the other of short cycle, labelled HA and HB respectively, were submitted to two pollination regimes: auto-pollination (bagged treatment) where the heads were covered with mesh bags from the first anthesis (FA) to the last anthesis (LA), avoiding the action of pollinators and open pollination (open treatment). The study was conducted during three consecutive years in two different locations. In the first year, the experimental plots were located at the Chacra experimental Barrow (Tres Arroyos; 38 degees 20 min S; 60 degrees 13 min W) and in the second and third year at the experimental field of Universidad Nacional del Sur, (Bahía Blanca; 38 degrees 45 min S; 62 degrees 11 min W), reaching an average plant density of 60.000 plants/ha. During the second year treatments were conducted only on the HA and during the third year only on the HB. The number of FDF and IDF, in the three experiments on both sites did not show significant differences among treatments. Nevertheless, a non-significant different response in the number of FDF and IDF was observed during two years, probably as a result of changes in environmental conditions during the anthesis period. We conclude that, due to the effect of a high level of self-compatibility, no differences in the generation of fully developed fruits can be observed when plants of modern commercial sunflower hybrids are excluded from pollinators.