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Kingdom |
Proteobacteria |
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Class |
Zymobacteria |
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Order |
Enterobacteriales |
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Family |
Enterobacteriaceae |
Bacterial stem and
root rot caused by Erwinia chrysanthemi can be economically important
because it destroys plants and fleshy roots. The amount of losses due to the
disease have not been reported.
E. chrysanthemi attacks several hosts in different regions of
the world. However, the disease on sweetpotato has only been reported from USA.
It is also suspected to occur in Central Luzon, Philippines.
This
disease is more common in storage but may also affect plants in the field and in
seedbeds.
The first symptom is the partial wilting of the plant; one or two branches
may wilt, and eventually the entire plant may collapse and die. Discolouration
of tissues inside the stem may also occur under some conditions.
Water-soaked, sunken brown to black lesions
are observed at the base of stems and on petioles. The disease initiates as
small spots that grow overnight and form
larger lesions.
On fibrous roots, localized lesions are observed, but the entire root system
can be affected, showing the characteristic black, water-soaked appearance.
There is also dark streaking in the vascular tissue of the roots.
On storage roots, small, sunken brown lesions with black margins can be
observed on the surface, but more frequently the rotting is internal with no
evidence outside. Affected tissue becomes watery. The disease is more common in
the storage than in the field.
The pathogen enters host tissue through wounds.
The characteristic evidence of this pathogen, as it occurs with some other
bacterial diseases, is the peculiar smell produced in infected tissues, due to
the invasion of saprophytes that live on decomposed organic matter.
E. chrysanthemi is a gram-negative
bacterium, non-spore forming, rod shaped, usually single cells of 0.5 - 0.7 x 1
- 2.5 µm, motile, because it has several peritrichous flagella, facultatively
anaerobic.
The pathogen lives in plant debris and in the roots as well as on soils
surrounding the roots of sweetpotato and its other hosts.
Dissemination is through infected planting material, irrigation water, tools,
animal grazing, shoes of labourers, etc.
Optimum disease development occurs at 30°C but the bacterium survives in a
wide range of temperature below 27°C. No other factors, aside from temperature,
have been reported to affect the development of the disease.
Pathotypes of E. chrysantemii have been reported to affect other
plant species, but no reference was made on sweetpotato.
E. chrysanthemi is pathogenic across a wide range of species.
The primary hosts are:Zea mays (corn), Sorghum bicolor (
sorghum), Sorghum Sudanensis (Sudan grass).
The secondary hosts include:Aechmeafasciata (urn-plant), Aglaonema
pictum (Chinese evergreen), Allium fistulosum (Welsh onion), Ananas
comosus (pineapple), Begonia bertini (begonia), Brachiara mutica (tall
panicum), Chrysanthemum spp. (Chrysanthemum), Colocasia esculenta (taro),
Dahlia spp. (dahlia), Daucus carota (carrot), Dianthus
caryiophyllus (carnation), Dieffenbachia spp. (dieffenbachia),
Dracaena marginata (Madagascar dragon tree), Euphorbia pulcherrima (poinsettia),Imperata
cylindrica (cogon grass), Ipomoea batatas (sweetpotato), Musa spp.(plantain),
Oriza sativa (rice), Panicum maximum (Guinea grass), Parthenium
argeratum (guayule), Paspalum sp.(paspalum), Pennisetum purpureum (elephant
grass), Petunia hybrida (Petunia), Phalaenopsis sp. (phalaenopsis),
Philodendron spp. (phylodendron), Saccharum officinarum (sugar
cane), Saintpaulia ionantha (African violet), Solanum tuberosum (potato)
and Syngonium podophylum (nephthytis).
Cultural control
Use of cuttings obtained from the uppermost portion or tips of vines.
Proper postharvest handling to avoid wounding the storage roots.
Crop rotation for at least three years with non-host crops.
Weed control.
Application of soil amendments to reduce soil acidity.
Host-plant resistance
Differences in susceptibility have been observed. Assays on resistance should
be tried with local varieties of sweetpotato.
Chemical control
No chemical control measures have been fully evaluated on sweetpotato.
Bradbury. J.F.1977. Erwinia chrysanthemi. CMI Descriptions of
Pathogenic Fungi and Bacteria No. 553 3 p.
Bradbury, J.F.1986. Guide to plant pathogenic bacteria. CAB International
Mycological Institute. Surrey, England. 332 p.
Clark, C.A. and Moyer, J.W. 1988. Compendium of sweet potato diseases. APS
Press. 74 p.
Contributed
by: Teresa Ames |
