|Arevalo Gardini, Enrique|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/8/1999
Publication Date: N/A
Citation: Interpretive Summary: The soil-inhabiting fungus Fusarium oxysporum f. sp. erythroxyli is currently causing a natural wilt epidemic on the narcotic plant coca in Peru. This work was undertaken to determine if this pathogen can be disseminated by infected seed. A total of 202 fruits from Peru and 69 from Hawaii (HI) were collected from plants with and without disease symptoms. The fruits were surface sterilized, dissected into 5 parts (layers), and plated onto agar medium. Both F. oxysporum and F. moniliforme were recovered from Peru, while only F. oxysporum was found in HI. These isolates were tested for their ability to cause disease on coca in the greenhouse. Out of 91 isolates of F. oxysporum, 21 were pathogenic to coca seedlings. Six of these were originally from the pedicel, 8 from the pericarp, 4 from the seed coat, and 3 from the endosperm. Most of the pathogenic isolates (76%) had been collected from plants with disease symptoms. The isolates were further characterized using RAPD and vegetative compatibility groups. These analyses indicated that there are two genetic populations of the pathogen in Peru and only 1 in HI. The 1 in HI is the same as one of the Peruvian populations. Thus, it is likely that the pathogen was brought from Peru to HI. These data indicate that infected seed may contribute to the dissemination of this pathogen. This information will be used by scientists studying the potential of F. oxysporum f. sp. erythroxyli as a potential mycoherbicide for control of coca.
Technical Abstract: Fusarium oxysporum f. sp. erythroxyli causes a vascular wilt of the narcotic plant coca. To determine whether this pathogen can be transmitted by infected seed, fruits from symptomatic and asymptomatic plants from different coca growing areas in Peru and from an experimental field site in Hawaii were collected, surface-disinfested and separated into five parts: pedicel, pericarp, seed coat, endosperm and cotyledons. After removal of pedicel and pericarp, seeds were 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 fruits. F. oxysporum was isolated from 33% of the fruits plated and 35% of these isolates were 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 fruits collected in Hawaii. Most of these isolates (59%) were from the pedicels of fruits from symptomatic plants. A total of 202 fruits from Peru and 69 fruits from Hawaii were dissected and plated. 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, 8 from the pericarp, 4 from the seed coat, and 3 from the endosperm. Most of the pathogenic isolates (76%) were from symptomatic plants. The genetic diversity of the pathogenic isolates was characterized using RAPD analysis and vegetative compatibility groups. Based on these analyses, two different subpopulations of the forma specialis erythroxyli were found in Peru while only one was present in Hawaii isolates. These data indicate that contaminated seed may contribute to dissemination of this pathogen.