Yield analysis of winter oilseed rape (Brassica napus L.): a review

This paper reviews the most important biological processes that determine the yield of winter oilseed rape (Brassica napus L.). Biological yield is the product of growth rate and duration of the growing period, both of which indicate the potential for improvement in yield. Likewise, a greater harvest index leads to a higher seed yield. A brief survey of five recently published rapeseed crop models is given. Most of these models are poor predictors of biomass and yield; there is a lack of information about key physiological processes involved in establishment of the stand, the production of biomass and formation of yield, cessation of growth in winter, flowering and post-anthesis growth. During flowering and pod set, the relation between source and sink regulates the availability of assimilates necessary for seed filling. The most source-limiting process is related to small photosynthetically active area, caused by a drastic decline in the leaf area index from the start of flowering despite a slow increase in the assimilating pod area. To analyse yield, it is necessary to understand the structure of the yield and the primary and secondary components, which determine seed yield. Plant density governs the components of yield and, thus, the yield of individual plants. A uniform distribution of plants per unit area is a prerequisite for yield stability. The number of pods per plant is decisive for seed yield; this trait is ultimately determined by the survival of branches, buds, flowers and young pods rather than by the potential number of flowers and pods. Seed number per pod is correlated with pod length. It is, therefore, concluded that pod length is a suitable trait for indirect selection in plant breeding.