YIELD FORMATION AND YIELD STRUCTURE OF WINTER OILSEED RAPE (BRASSICA-NAPUS L) .1. GENOTYPIC VARIABILITY

In a field experiment, 10 varieties/lines of winter rapeseed (Brassica napus L.) were grown in northern Germany (Schleswig-Holstein) during three years of testing. The study was conducted to analyse genotypic variability in yield formation and yield components. Start of flowering, duration of silique maturation and total vegetative period varied within 8 days. Maximum growth rates amounted to 2.10 up to 2.83 dt . ha-1 . d-1 and, on the average were reached 10-13 days after start of flowering. However, three varieties were characterized by delayed maximum growth rates occurring at 15-17 days after start of flowering. The relative proportions of generative and vegetative dry matter changed with time. Genotypic differentiation was observed for silique index which was defined as share of siliques in above ground biomass. The corresponding values ranged from 64 % to 56 % whereas harvest index referring to percentage of seeds in shoot dry matter amounted to 31 % up to 38 %. To characterize the assimilatory surface, leaf area index (LAI) and silique area index (SAI) were investigated. During late autumn, LAI had increased up to 3. Due to losses of leaves during the winter season, LAI declined to 1 on the average while for two varieties LAI even decreased to 0.5. During spring, LAI re-increased and maximum values of 3.7 were measured. Thereafter, the leaf area was reduced again. Huge genotypic variation in leaf area development was observed. Some varieties/lines revealed highest LAI values before flowering whereas, others reached maximum LAI only at start of flowering. After the flowering period, silique area contributed considerably to stand assimilation. Maximum SFI climbed up to 4 thus, exceeding maximum LAI. Genotypic variation in SFI was proved in relation to branching capacity of individual plants. LAI of the juvenile stages but also maximum LAI were closely related to acreage yield as indicated by high genotypic coefficients of correlation. Yield composition of varieties/lines varied independently of yield level. E.g., high yields could be reached at different combinations of three yield components, number of siliques, seeds per silique and individual seed weight. As to indirect selection, dry matter before flowering, maximum leaf area index, harvest index and dry matter at maturity have to be aimed at. Furthermore, a defined yield structure should improve the choice of parental lines in breeding programmes including hybrid structures. As to rapeseed cropping, agrotechnical measures should be directed specificly to varieties.