APS Abstracts of Presentations

Fungal colonization in phloem/xylem tissues of taproots in relation to foliar symptoms expression of soybean sudden death syndrome. X. B. YANG and S. S. Navi. Iowa State University, Dept. of Plant Pathology, Ames, IA 50011. Phytopathology 93:S92. Publication no. P-2003-0680-AMA.

Current resistance screening methods for soybean sudden death syndrome caused by Fusarium solani f. sp. glycines (FSG) are inconsistent in foliar symptom expression. Studies were conducted to determine the cause of inconsistence. Germinated soybean seeds with 1-cm radicle were dip-inoculated in spore suspension before transplanted. Three weeks later plants were assessed and grouped by presence of foliar symptoms. Discoloration in phloem or xylem tissues of tap roots were assessed and isolations were made to confirm FSG colonization in each tissue. All inoculated plants had discolored phloem tissue in taproot. However, discoloration was limited to phloem cylinders in plants without foliar symptoms. Discoloration occurs in both phloem and xylem tissues in plants with foliar symptoms and isolations confirmed colonization of FSG in xylem tissue. Our data suggest that 1) fungal colonization in xylem is critical to foliar symptom expression; 2) radicle infection increases likelihood of fungal colonization in xylem.