Potential for dispersal of Fusarium oxysporum f. sp. erythroxyli by infested seed

Fusarium oxysporum f. sp. erythroxyli causes a vascular wilt of the narcoti c plant coca (Erythroxylum coca var. coca). To determine whether this patho gen can be transmitted by infested seed, fruit from symptomatic and asympto matic plants was collected from different coca-growing areas in Peru and fr om an experimental field site in Hawaii. A total of 202 fruit from Peru and 69 fruit from Hawaii were surface-disinfested and separated into five part s: pedicel, pericarp, seed coat, endosperm, and cotyledons. After the pedic el and pericarp were removed from the seed coat, the seed was surface disin fested again. Each fruit part was plated separately. Both F. oxysporum and F: moniliforme were recovered from fruit collected in Pem. Both species wer e isolated from all parts of some fruit. F. oxysporum was isolated from 33% of the fruit plated and most (35%) of these isolates were obtained from th e seed coat. Slightly greater numbers of isolates (57%) were recovered from asymptomatic plants than from symptomatic plants (43%). Only F. oxysporum was isolated from fruit collected in Hawaii. Most of these isolates (59%) w ere from the pedicels of fruit collected from symptomatic plants. Out of 91 isolates of F: oxysporum, 21 were pathogenic to coca seedlings in a bioass ay. Six of these pathogenic isolates were originally from the pedicel of th e fruit, eight from the pericarp, four from the seed coat, and three from t he endosperm. No isolates from the cotyledons were pathogenic. Most of the pathogenic isolates (76%) were from symptomatic plants. The pathogenic isol ates were characterized using random amplified polymorphic DNA analysis and vegetative compatibility groups. Based on these analyses, two different su bpopulations of the forma specialis erythroxyli were found in Peru, whereas only one was present in Hawaii. These data indicate that infested seed may contribute significantly to dissemination of this pathogen because seed is collected by growers and planted fresh or fermented briefly before plantin g.