|
|
Kingdom |
Fungi |
|
Phylum |
‘mitosporic
fungi’ |
|
Class |
Coelomycetes |
The disease is of
low importance but it can pose a considerable problem when slightly infected
storage roots are stored.
In Argentina
losses in the field of 25 to 75% have been reported in the past.
Apparently the disease is present mainly in the western hemisphere. It has
been reported in Argentina, Brazil, Caribbean, Peru, and USA.
In seedbeds, seedlings show yellowing, especially, of the lower leaves. Later
on, plants wilt and die.
In the field, plants show a blackening of the vine around soil level,
extending upwards and downwards. The lower portion of the stems rot.
Disintegration of the root system occurs. Affected stems may be girdled and the
plant dies. Black pycnidia develop in affected areas of the stem and roots.
In storage, roots start rotting from the end that has been attached to
the mother root (proximal). Affected roots develop a firm, dry, dark brown decay
that covers a large portion of the root.
The conidia are one-celled, oblong,
sometimes slightly curved, have rounded ends, hyaline,
bigutulated, and measure 6 - 10 x 3-4 µm. Long, hyaline, sometimes curved
stylospores that measure 5 -15 µm are also present. The pycnidia
are black, round, partially submerged in affected tissue, and form
concentrations of more than 2 structures with straight or curved beaks that
measure 100-500 x 80-200 µm.
Very little is known about the biology of the fungus. It has been observed
that survival in the field is very poor, so the main way the disease is
perpetuated is when infected cuttings are used for planting. The influence of
soil composition, moisture, temperature and rainfall has not been studied.
In places where storage roots are used as source of planting material, the
disease is transmitted from the sprouts and cuttings.
Ipomoea batatas (sweetpotato) is up to now the only economically
important host. The disease also attacks some other Convolvulaceous hosts.
In the field, the disease can be diagnosed by the blackening of
the stem base and the portion a little below the soil level. In storage the
presence of the disease can be observed when the periderm of affected fleshy
root is pulled off and the black pycnidia are present.
Cultural control
Plant cuttings from healthy plants.
Two-year soil rotation is recommended.
Host-plant resistance
In Brazil the cultivar ‘Princesa’ have been found to show less disease
than other popular cultivars.
Chemical control
Thibendazole can be used in disinfecting planting materials.
Clark, C. A. and Moyer, J.W. 1988. Compendium of sweet potato diseases. APS
Press. 74 p.
Fresa, R. y Corvalio, F. 1966. Podredumbre del pie de la batata (Plenodomus destruens). Revista
de Investigaciones Agropecuarias INTA - Argentina. Serie 5. Patologia Vegetal.
Vol III No.6: 47-58.
Lopes, C.A. and Silva J.B.C. 1993.Management measures to control foot rot of
sweet potato caused by Plenodomus destruens. International Journal of
Pest management 39:72-74.
Contributed
by: Teresa Ames |
