The effect of autopolyploidy on biomass production in homozygous lines of Brassica rapa and Brassica oleracea

In Brassica species contradictory results on the effect of polyploidization on vegetative biomass production have been reported. This might result from the fact that the level of heterozygosity in diploid and tetraploid lines as a major factor of plant performance in Brassicas is often disregarded. Therefore in this study autotetraploid lines were developed from seven completely homozygous lines of B. rapa and B. oleracea in order to analyse the unconfounded effect of polyploidy on vegetative biomass production of young plants. The tetraploid lines yielded 2-64% less than the corresponding diploid lines and there was no significant effect of the ploidy level on the dry matter content. These results indicate that the direct effect of polyploidization in B. rapa and B. oleracea is negative while in some other studies this negative effect could be compensated by a higher level of heterosis in tetraploid populations compared to their diploid reference populations.