WHITE FLOWER COLOR IN RAPE (BRASSICA NAPUS) ASSOCIATED WITH A RADISH (RAPHANUS SATIVUS) CHROMOSOME

The inheritance of flower color was investigated in progeny from crosses between a normal, yellow flowering rape strain (Brassica napus L.) and a white flowering strain developed at the University of Manitoba by backcrossing the white flower color from Raphanobrassica into B. napus. The chromosome number of all yellow flowering plants examined was normal (2n = 38), whereas all white flowering plants examined contained a single or a pair of small radish (Raphanus sativus L.) chromosomes each carrying a dominant gene(s) for white flower color. The homozygous white flowering rape strain was in fact an alien addition line (2n = 40) disomic for a pair of radish chromosomes. The transmission and meiotic behavior of this alien chromosome as a univalent was investigated in the progeny of crosses involving the white flowering F1 hybrid. Cytological observations of meiotic metaphase 1 indicated that the univalent should be transmitted with 24.6% of the gametes. This was in agreement with the observed transmission of 24.3% through the female gametes. Transmission through the pollen ranged from 22.1% to 0.7%, the variation in certation depending on the genetic constitution of the pistil and on the time of pollination. The vigor, fertility and true breeding nature of the white flowering strain suggested that the white flower color factor from the radish had been introgressed into the rape genome. Cytological observations were necessary to demonstrate that introgression had not taken place and to aid in the interpretation of the genetic ratios observed.