Relation of sand content, pH, and potassium and phosphorus nutrition to the development of sudden death syndrome in soybean

Development of sudden death syndrome (SDS) of soybean (Glycine man L. Merr. ), caused by Fusarium solani (Mart.) Sacc. f. sp. glycines (Fsg), was studi ed in relation to sand content, pH, and potassium and phosphorus nutrition under controlled environments. Incidence and severity of SDS increased by a pproximately two- and four-fold, respectively, as the sand content in soil increased from 53 to 100%. Disease severity increased by an average of 21% at soil pH = 7.7 compared to pH = 5.5. Amending the soil with potassium chl oride resulted into an average decrease of 36% in SDS severity compared to the control; conversely, disease severity was increased by an average of 21 % with calcium phosphate, 32% with potassium phosphate, 43% with potassium sulfate and sodium phosphate, and 45% with potassium nitrate compared to th e controls. In vitro conidial germination of Fsg was not significantly affe cted by potassium and phosphorus amendments. However, mycelial linear growt h was enhanced by an average of 15, 22, and 25% with potassium nitrate, pot assium phosphate, and sodium phosphate, respectively but not with potassium chloride, potassium sulfate, or calcium phosphate. Colony area increased w ith increasing pH and was approximately 2.5-fold greater at pH = 8.2 than a t pH = 5.7. Collectively, these results indicate that the physical and chem ical environments of soil exert a significant effect on SDS in soybean and on Fsg.