COTYLEDON CELL NUMBER AND CELL-SIZE IN RELATION TO SEED SIZE AND SEEDYIELD OF SOYBEAN

The objective of this study was to determine nutrient-related changes in cotyledon cell size and cell number. These parameters are known to be related to genotypic differences in seed size and consequently fina l seed yield of soybean (Glycine max L. Merr). Greenhouse-grown soybea n plants received an initial fertilizer (N-P-K) application at plantin g. Later, two groups of plants received supplemental fertilizer either at early pod set only (Group I) or at both anthesis and pod set (Grou p II). Plants in Group I had the highest number of pods, seeds and tot al seed yield per plant relative to controls and Group III plants. Dry weight and size (volume) of individual seeds was also the highest in Group I plants. The number of cells per cotyledon as determined by bot h counting the cells under a microscope and by measurement of total se ed DNA indicated that application of supplemental fertilizer at either stage did not increase the number of cells within each seed. Cell siz e in Group I and Group II plants was however, 59% and 40% higher than that of controls, respectively. Enhanced seed yield in Group I plants appeared to have resulted from increased cell size (and consequently s eed size) and seeds per plant. Similar results were observed in field- grown soybeans planted in high density plots. While genotypic differen ces in soybean seed size may be, to a large extent, determined by cell number, within a single genotype, seed size may be influenced more by cotyledon cell size than cell number.