Variation in quality of individual seeds within a seed lot of soybean (Glycine max (L.) Merrill)

The research described in this thesis aimed at increasing insight into the sources of variation in quality attributes of individual seeds within a soybean seed lot, into the relations between physical attributes and performance of seeds in seed tests and in controlled seed production conditions, and into the importance of the seed lot quality for crop performance including quality of seeds produced. Cv. IAS-5 (determinate growth habit) was used in all studies. Differences in characteristics within and between plants proved to be important sources of variation in size, weight, shape, viability, and performance of individual seeds in the seed lot produced. Seeds from earlier pods were larger, heavier, more spherical but less viable than from later pods. Seeds from main stems or from the top of the plants were larger and heavier than seeds from the branches or from the bottom of the plants. At these positions also pod set was earlier. Shorter times to emergence and longer periods from first pod set to harvest were associated with larger sizes of seeds produced per plant. Longer periods between first flower and first pod, and shorter periods between first pod and harvest were related to a higher viability of seeds produced per plant, but only under high air temperatures during pod growth and maturation. Within the seed lot studied, different physical seed attributes were associated. Etching and cracking were more frequent in larger and heavier seeds, yellow seeds were larger than greenish seeds. Taking into account these associations was essential to correctly assess the actual contribution of individual attributes to seed performance. Distinct tests assessed different attributes as being important. The tetrazolium test detected etched, cracked, greenish and wrinkled seeds. Conductivity per seed was affected by seed size, weight, cracking and wrinkling. Conductivity on a seed area projection basis (μA/mm 2) was shown to minimize size and weight effects. In this case, also higher conductivity values for greenish seeds were detected. Some individual physical seed attributes affected distinct stages of seedling growth differently. Therefore, conclusions on the importance of physical attributes for seed performance in seedling growth tests may depend on the stage of seedling growth at the time of analysis. Size, weight, shape, etching and wrinkling of seeds planted in soil were not related to emergence under favourable conditions, but fewer seedlings emerged from cracked and from greenish seeds. Within a crop, yield components per plant (number of pods or seeds, total weight of seeds) decreased with increasing size, weight and cracking of the seeds planted. In none of the crops physical attributes of individual seeds planted were associated with quality attributes of the seeds produced by them. Effects of seed lot grading for physical attributes on crop uniformity, and on quality, uniformity and yield of the seeds produced could not be shown. <br/

Uniformity, performance and seed quality of soybean (Glycine max (L.) Merrill) seed crops grown from sub-samples of one seed lot obtained after selection for physical seed attributes

In a glasshouse experiment it was examined whether narrow grading and selection from a commercial soybean seed lot cultivar ‘IAS-5’, could improve the uniformity of the seed crop grown from it and thereby enhance yield, quality and uniformity of seeds produced. The classes created were: Control (original seed lot); Size-graded seeds (projected area measured by image analysis 37–46 mm2); Non-cracked seeds; Yellow seeds; Size-graded sound seeds (size-graded, non-cracked, yellow, non-wrinkled, non-etched). Compared to the control, percentage of emergence, survival and number of yielding plants were enhanced in crops from non-cracked, yellow or size-graded sound seeds. Differences in plant numbers did not result in differences in crop yield. The different seed lots also did not differ in crop uniformity: time interval between stages of plant development, plant height 20 days after sowing, yield components, physical or physiological quality attributes of seeds produced, and respective coefficients of variation were similar. Fewer plants survived in crops showing a larger variation in plant height 20 days after sowing, thus reducing differences in initial plant-to-plant variation. Creating more uniform crops by additional grading or selection of commercial seed lots may therefore not be promising

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