Effects of the 'Stay Green' Genotype GGd1d1d2d2 on Leaf Gas Exchange, Dry Matter Accumulation and Seed Yield in Soybean (Glycine max L. Merr.)

The homozygous combination of the recessive mutations d1 andd2, i.e.d1d1d2d2 , causes retention of chlorophyll, chlorophyll-bindingproteins and Rubisco in senescing leaves of soybean (Glycinemax L. Merr.). Together with G(a gene that preserves only chlorophyllin the mature seed coat), d1d1d2d2 prolonged photosyntheticactivity and increased seed yield in growth chamber experiments.The objective of this work was to test the effects of GGd1d1d2d2(abbreviatedto Gd1d2) on leaf gas exchange, growth and seed yield in soybeanplants cultured outdoors during the normal growing season. Despitepreservation of the photosynthetic machinery in Gd1d2, photosynthesisduring the seed filling period was similar in Gd1d2 and itsnear-isogenic wild type line ‘Clark’. The main factorlimiting photosynthesis in the mutant appeared to be stomatalconductance, which was substantially lower in Gd1d2 than in‘Clark’. In Gd1d2 the rate of dry matter accumulationduring the seed filling period was similar or lower than inthe wild type. At maturity, Gd1d2 had fewer nodes, fruitingnodes, fruits and seeds per plant, and therefore its seed yieldwas reduced by 10–20% compared to ‘Clark’.Thus, pleiotropic effects of G, d1 and/or d2 affecting stomatalconductance and seed number appear to be major limitations tothe yield potential of Gd1d2. These pleiotropic effects suggestthatG , d1 and/or d2 have regulatory functions in addition tothe control of chloroplast disassembly during senescence. Copyright2001 Annals of Botany Company Glycine max L. Merr., photosynthesis, seed yield, senescence, soybean, stay green, stomatal conductance