Effects of weather conditions during different growth phases on yield formation of winter oilseed rape

•WOSR yield is determined during onset of pods and seeds and seed development.•Weather conditions determine duration and rate of assimilate production.•WOSR has a compensatory effect between number of seeds per m2 and 1000-seed weight.•WOSR yield is mainly source-limited, especially during the late reproductive phase.

Winter oilseed rape (WOSR) is an important oil and protein crop in Europe, used in biofuel production and as protein source in livestock farming. In contrast to cereals, WOSR seed yields are still increasing in most countries but yield stability was not improved during the last decades.In our study, we analyzed the effects of weather conditions during different growth stages on maximum seed yield, maximum oil yield, number of seeds per m2 and 1000-seed weight to get further information on yield formation processes.Field trials performed at 34 environments (site × year combinations) representing different soil characteristics and climate regions in Germany were used for the analysis. About 40% of seed yield variability could be explained by weather conditions during specific growth phases. The most important phenological phases thereby were: onset of pods and seeds (BBCH 50–65) and seed development (BBCH 71–79). During onset of pods and seeds, yield was significantly influenced by temperature, radiation and drought stress. Assimilate availability during this phase determines the number of seeds per m2 (sink size). After flowering, only temperature significantly affected WOSR yield. Temperature is the major parameter determining the duration of growth stages. Lower temperature elongates the time of assimilate production and translocation to the seeds. During this growth stage, seed weight is determined. In our data sets, low sink size was not yield limiting due to compensatory effects between the yield components number of seeds per m2 and 1000-seed weight. Yield response pattern suggests that WOSR yield is predominantly source-limited, especially during the late reproductive phase.