Phomopsis Seed Infection and Nutrient Accumulation in Pods of Soybean with Reduced Fruit Loads

Abstract

AbstractActive infection of soybean [Glycine max (L.) Merr.] fruits by Phomopsis longicolla Hobbs is associated with physiological changes occurring during senescence. The purpose of this research was to determine the relationship of carbohydrate and mineral nutrient composition of pod tissue to seed infection by P. longicolla. Varying carbohydrate and mineral nutrient levels in pod tissue were created by different fruit removal and debranching treatments. Reducing fruit load in plants from three to four pods per node to one per node increased seed infection by P. longicolla 42% and decreased seed germination 35%. Total nonstructural carbohydrates, N, and P concentrations in pod walls at physiological maturity were increased 56, 40, and 77%, respectively, by pod reduction. Seed total nonstructural carbohydrates were reduced 13% and seed N increased 15% by reduced fruit loads. Fruit removal delayed plant maturation up to 2 to 3 wk. A lower incidence of P. longicolla and moldy seed from upper nodes (vs. lower nodes) of plants was associated with lower K and greater Ca and total nonstructural carbohydrates in pod walls. Decreasing seed infection by P. longicolla might be achieved by maximizing fruit loads and shortening the time interval between physiological maturity and harvest maturity.