SHADE INDUCED CHANGES IN FLOWER AND POD NUMBER AND FLOWER AND FRUIT ABSCISSION IN SOYBEAN

Seed number per unit area is important in determining yield in soybean [Glycine mar (L.) Merr.]. Field and greenhouse experiments were conducted to evaluate the role of flowers per plant and flower and fruit abscission in determining pod and seed numbers. Two greenhouse experiments were conducted with the McCall cultivar [Maturity Group (MG) 001 and four cultivars [McCall, Hardin (MG I), Harper (MG III), Essex (MG V)] were used in field experiments in 1989 and 1990. The field experiments used either 0.38-m (McCall and Hardin) or 0.76-m rows (Harper and Essex) with a constant seeding rate of 26 seeds per meter. Shade cloth (63% in the greenhouse and 30 and 63% in the field) was placed over plants from R1 to maturity. Additional treatments in the greenhouse included shade from R1 to R4, R4 to R5, R5 to R6, and R4 to R8. Plants were harvested at maturity and flower and pod abscission was determined by counting both the scars marking the point of attachment of flowers and pods, and mature pods. Shade reduced pod numbers and the reductions were due to both increased flower and pod abscission and fewer flowers per plant. Both the number of nodes on the main stem and flowers per node were affected by the shade. Shade during any part of the R1 to R6 period reduced pod numbers in the greenhouse. These data indicate that environmentally induced variation in pod numbers in soybean is a result of both changes in flower and fruit abscission and the number of flowers produced.