Morphological traits and genetic diversity of differently overwintered oilseed rape (Brassica napus L.) cultivars

Winter oilseed rape is an important crop grown in many countries for its valuable oil and protein. One of the main problems of cultivating rapeseed in northern countries is winter survival. The objective of this study was to assess morphological traits and genetic diversity of eleven cultivars of winter oilseed rape (Brassica napus L.) grown in experimental fields and to determine the correlation between phenotypic variation, deoxyribonucleic acid (DNA) polymorphism and overwintering characteristics. Oilseed rape stand density, height of growth point from the soil surface, thickness of root neck as well as the number of developed leaves per plant were observed for morphological traits analysis. The number of owerwintered plants was evaluated. The genetic variability of 11 oilseed rape cultivars was evaluated by random amplified polymorphic DNA (RAPD) screening 14 primers, 9 of them being polymorphic and used for further analysis. A total of 84 reproducible RAPD bands were identified among 134 individuals, 73 of the detected DNA bands were polymorphic. Among cultivars Nei's gene diversity ranged in the interval 0.1344-0.0313, Shannon's information index was 0.2022-0.0449. An analysis of molecular variance (AMOVA) showed a significant genetic diversity among populations (Phi(PT)=0.684,p<0.01). Unweighted pair group with arithmetic mean (UPGMA) cluster analysis dendrogram generated on the basis of 73 polymorphic RAPD bands showed a clear separation of all analysed cultivars to different clusters. Dendrogram constructed using five morphological traits divided 11 oilseed rape cultivars into two clusters with one stand-alone cultivar 'DK Secure'. No significant correlation of genetic diversity with morphological traits was obtained. A strong and significant correlation between the oilseed rape overwintering capability and the number of polymorphic loci was obtained only in 2008-2009 season (r = 0.81,p = 0.03).