POLLEN SIZE AND PLOIDY LEVEL IN THE GENUS ROSA

Pollen size is generally influenced by internal and external factors (genetical and environmental). Often, many species show a positive correlation between pollen size and the number of chromosome or the ploidy level, which are stable factors for homozygote genotypes (A. Katsiotis et al., 1995). In genus Rosa, 2x, 3x, 4x, 5x, 6x and 8x exist more or less naturally and the floral biology of these species has been little studied up till now. Morphology of Rosa pollen was studied with scanning electron microscopy (Y. Ueda et al., 1989), but no relation was made with ploidy level. Interest to find a correlation between these parameters is justified by :

1. The interfertility of different species, belonging to different botanical sections and having different ploidy levels.
2. The low knowledge level of behaviour of Rosa species in a breeding program, particularly in terms of consequence of presence of unreduced pollen related to the success of crosses.