Time of pod set and seed production on the plant contribute to variation in quality of seeds within soybean seed lots

Time to pod set and seed position on the plant were studied as possible within-plant components contributing to variation in quality of seeds within seed lots of soyabean (Glycine max) cultivar IAS-5. Plants were grown at 28/22°C (NT=normal temperatures) or 33/27°C from the beginning of pod set onwards (HT=high after normal temperatures). The heaviest seeds were produced on positions in the canopy where also the earliest pods were formed: main stems versus branches and upper versus lower main stem sections. The variation in weight between seeds within a seed lot was mainly determined by position in the canopy, contributing 23 and 30% under NT- and HT-conditions, respectively. Days to pod set contributed 2 and 27% respectively. Position fully accounted for variation resulting from days to pod set under NT- but not under HT-conditions. Seeds from earlier pods had a lower viability. For explaining differences in viability between seeds within a seed lot, days to pod set of individual seeds was more important than seed position. Components of variation between plants were largely additional to within-plant components and at least of equal importance.