Associations of Plant Symptoms and Pod Position with Phomopsis sojae Seed Infection and Damage in Soybean1

Abstract

The frequency and severity of infections of Phomopsis sojae (Leh.), pod and stem blight fungus, were inversely related to pod height on soybean [Glycine max (L.) Merr.] plants for the cultivars ‘Chippewa 64’ ‘Hark’, and ‘Wells’. Phomopsis sojae seed damage was primarily found in the bottom third of plants and distribution of damaged seed was heavily skewed to the lowest bearing node. Overall USDA soybean grades were lowered for Chippewa 64 and Wells due to seed damage caused by P sojae. Disease ratings based on stem, pod, and seed symptoms were tested for their association with seed infection rates. Visible symptoms rating for seed was highly associated with rates of seed infection for all cultivars. Pod and stem symptom ratings were highly associated with seed infection rates in Chippewa 64 and Wells but not for Hark. Selective harvest of upper plant portions improved seed quality.