REPRODUCTIVE DEVELOPMENT OF AN INDETERMINATE SOYBEAN AS AFFECTED BY MORPHOLOGICAL POSITION

The indeterminate growth habit of some soybean [Glycine max (L.) Merr. ] cultivars results in sequential grain setting; thus, knowledge of th e reproductive development of soybean is important for understanding y ield variability. The objective of this study was to investigate the i nfluence of the timing of flowering and the morphological position of reproductive organs on individual seed development and growth. 'Maple Arrow' plants, Maturity Group 00, were grown under field conditions in Guadeloupe (French West Indies, ferralic Fluvisol) for 2 yr and at Di jon (France, clayey Eutric Cambisol) for 1 yr, with various treatments including different sowing densities, a depodding treatment, and N su pply during seed filling. Regardless of their morphological position, reproductive organs that flowered simultaneously also reached the begi nning and termination of seed filling simultaneously. Thus, the lag-ph ase duration and the duration between flowering and physiological matu rity were Linearly related to timing of flowering. Slopes for both rel ationships were significant for all treatments and locations. Converse ly, timing of physiological maturity was variable among treatments. Th e onset of physiological maturity seemed to be determined by the time when N reserves of vegetative parts were exhausted. However, individua l seed size seemed to determine physiological maturity when sources we re greater than sinks. On the other hand, morphological position had a great effect on growth of individual seed, whereas timing of flowerin g was the main determinant of further seed development. Organization o f reproductive development of the whole plant depends strongly on the timing of flowering of each reproductive organ. Conversely, the occure nce of physiological maturity of the whole plant and individual seed g rowth probably depends on the amount of available assimilates during s eed filling.