|
| Kingdom |
Fungi |
| Phylum |
‘mitosporic fungi’ |
| Order |
Coelomycetes |
Charcoal rot is a minor disease that can damage sweetpotato
roots in storage. Losses, however, are seldom serious.
The fungus is widespread in tropical and subtropical regions of
the world.
The disease only normally affects fleshy roots in
storage. However, stem may sometimes show lesions at the soil line during
heat stress.
Once the fungus enters the root, the disease initially develops
in the cortex, then crosses the vascular
tissue and finally decays the entire root.
Affected fleshy roots dry up, become spongy and hard, but
the periderm
(skin) remains intact over the
decayed tissue.
Two zones can be differentiated from a cross section of an
infected root: the outer zone which is black due to the presence of mature
sclerotia, and the inner zone where the tissue is reddish brown and is in the
process of decaying.
Only the anamorph
with mycelium and sclerotia
has been found in sweetpotato. The later is formed underneath the skin of fleshy
roots. Sclerotia are black, smooth, hard, from very small up to 1mm in
diameter.
The fungus is a saprophyte
and survives in the soil for several years as free sclerotia. The pathogen
invades the root tissues through wounds by producing black sclerotia confined in
the cortex and rot that can consume the entire root.
The disease spreads from one field to another by irrigation
water, animals, and farm implements. It becomes severe at high temperatures (35
- 39°C) and high moisture.
Antagonists: Aspergillus niger, Trichoderma terricola and
T. viride.
Sweetpotato (Ipomoeae batatas) is considered a primary
host. However, it has a wide range of hosts and is parasitic to tropical and
subtropical crops.
Sclerotia provide the most important diagnostic feature of the
disease in storage. These black structures on the infected tissues have a gritty
or sandy-like feel and are not present in storage roots infected with Java black
rot and black rot, the two storage diseases that charcoal rot can be being
confused with.
Cultural control
Use of clean and disinfected storage facilities and containers.
Avoidance of leaving harvested fleshy roots under the
scalding sun after harvest.
Avoidance of wounding the roots during harvest and handling.
Cure of roots before storage. Storage roots should be cured at 28-32°C and
90-95% RH for 10-14 days depending on the cultivar.
Maintenance of storage temperature at 15-16oC . High
temperature should be avoid ed in storage.
Host-plant resistance
Certain levels of resistance have been observed in different
cultivars
Chemical control
No chemical control is being used.
Ames, T., Smit,
N.E.J.M., Braun, A.R., O’Sullivan, J.N., and Skoglund, L.G. 1996. Sweetpotato:
Major pests diseases, and nutritional disorders. International Potato Center
(CIP). Lima, Perú. 152 p.
Holliday, P. & Punithalingam, E. 1970. Macrophomina
phaseolina. CMI Descriptions of Pathogenic Fungi and Bacteria. No. 275. 2 p.
Vasquez,
E.A. and Sajise, C.E. 1989. Pests of sweet potato: Insects, mites and diseases.
PRIS and PRCRTC, Visayas State College of Agriculture, Baybay, Leyte,
Philippines. 66 p.
Contributed
by: Teresa Ames |
