First Report of Dieback Caused by Verticillium dahliae on Blighia sapida in the United States.

Mature akee trees, Blighia sapida K. Koenig, in a local south Florida commercial orchard had wilt and dieback symptoms during spring 1999. A fungus isolated from the gray xylem root tissue on V8 agar was identified as Verticillium dahliae Klebahn at the Division of Plant Industry of the Florida Department of Agriculture and Consumer Services. Twenty akee seedlings were transplanted into 3.85-liter plastic pots and grown in a greenhouse at a daytime temperature of 28°C and nighttime temperature of 23°C. When plants were approximately 25 cm high, a 15-cm knife was used to sever roots in the four quadrants of each pot. Inoculum was made from a 2-week-old culture of V. dahliae on V8 agar and blended with 160 ml of sterile water, and 15 ml of this slurry was poured into the disturbed soil of each of 10 treated plants. A plate of uninoculated V8 agar was applied, as above, to 10 control plants. Plants were kept in the greenhouse. After 6 weeks, inoculated plants showed symptoms of leaf wilt, dieback and plant death. No symptoms were seen on control plants. V. dahliae was isolated directly from the gray vascular tissue of inoculated plants. The inoculation experiment was repeated three times, fulfilling Koch's postulates. To our knowledge, this is the first report of Verticillium dieback on B. sapida in the United States.