Collar Rot and Wilt of Yellow Passion Fruit in Venezuela.

Surveys were conducted to determine the occurrence of diseases of yellow passion fruit (Passiflora edulis f. flavicarpa) in plantations located in the central states of Aragua, Carabobo, Guarico, Miranda, and Yaracuy, Venezuela, from 1991 to 1998. Plants in both commercial plantations and passion fruit nurseries were symptomatic for wilt and reddish-brown collar rot. Symptomatic tissues were surface-disinfected and plated on PARPH medium (1). Phytophthora parasitica was frequently isolated from diseased tissues, and pathogenicity tests were conducted with the fungus under greenhouse conditions. Passion fruit seedlings were grown in pots containing a 1:1 (vol/vol) steamed soil/sand mixture, one plant per pot. Five-millimeter-diameter plugs of P. parasitica isolates were grown on clarified V8 agar. Three-month-old seedlings were wounded with a sterile scalpel in the collar region. Wounded and unwounded plants were inoculated with 10 ml of zoospore suspension (10⁵ spores per ml) or sterile water (control). Fifty plants were evaluated per treatment, and the experiment was repeated. Wounded and unwounded seedlings inoculated with zoospores developed chlorosis and collar necrosis after 15 days. Seedling mortality reached 50% 1 month after inoculation, and the fungus was reisolated from symptomatic tissues. This is the first report of P. parasitica causing collar rot and wilt of yellow passion fruit in Venezuela. Reference: (1) S. N. Jeffers and S. B. Martin. Plant Dis 70:1038, 1986.