Foliar symptoms expression and early infection of soybean sudden death syndrome
M. L. ZACCARON (1), X. Yang (1), S. S. Navi (1)
(1) Iowa State University, Ames, IA, U.S.A.
Phytopathology 100:S144

Soybean sudden death syndrome (SDS), caused by Fusarium virguliforme, is an important root disease that can express foliar symptoms leading to defoliation and yield reduction. Our earlier report showed that root cap is one of the penetration sites of infection for F. virguliforme, which will be followed by foliar symptoms in soybean. There is not much information about infection process of SDS and how environmental conditions influence the process and subsequent foliar symptoms development. The objective of this study was to investigate infection sites on soybean roots leading to foliar symptoms expression. Seeds were germinated using paper towel method at room temperatures; radicles of 72-h were inoculated with 20 µl of conidial suspension F. virguliforme using inoculation loop and micropipette methods under sterile conditions. Three sites of infection on different locations were examined. After inoculation germinating seeds were transplanted to cones filled with sterile potting mixture. Rhizosphere temperature was controlled with water bath at (20°C). Plants were evaluated three weeks after transplanting. Our preliminary results indicate that plants inoculated at root tip had higher incidence than plants inoculated at other sites. The incidence was even higher when the inoculation loop was used, suggesting mechanical wounding early at soybean planting may be critical to foliar symptom expression.