Authors
J. A.
Gracia-Garza
,
D. R.
Fravel
, and
A. J.
Nelson
,
Biocontrol of Plant Diseases Laboratory
;
K. S.
Elias
,
Systematic Botany and Mycology Laboratory
; and
B. A.
Bailey
,
Biocontrol of Plant Diseases Laboratory, USDA-ARS, Beltsville, MD 20705
;
E. Arévalo
Gardini
,
Universidad Nacional Agraria de la Selva, Tingo María, Perú
; and
L. C.
Darlington
,
Weed Sciences Laboratory, USDA-ARS
ABSTRACT
Fusarium oxysporum f. sp. erythroxyli causes a vascular wilt of the narcotic plant coca (Erythroxylum coca var. coca). To determine whether this pathogen can be transmitted by infested seed, fruit from symptomatic and asymptomatic plants was collected from different coca-growing areas in Peru and from 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 parts: pedicel, pericarp, seed coat, endosperm, and cotyledons. After the pedicel and pericarp were removed from the seed coat, the seed was surface disinfested again. Each fruit part was plated separately. Both F. oxysporum and F. moniliforme were recovered from fruit collected in Peru. Both species were 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 the 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%) were from the pedicels of fruit collected from symptomatic plants. Out of 91 isolates of F. oxysporum, 21 were pathogenic to coca seedlings in a bioassay. Six of these pathogenic isolates were originally from the pedicel of the fruit, eight from the pericarp, four from the seed coat, and three from the endosperm. No isolates from the cotyledons were pathogenic. Most of the pathogenic isolates (76%) were from symptomatic plants. The pathogenic isolates were characterized using random amplified polymorphic DNA analysis and vegetative compatibility groups. Based on these analyses, two different subpopulations 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 planting.
