The main fungal diseases of cassava are listed. They include leaf spot disease of minor importance caused by
Cercospora henningsii
Allesher,
C. caribaea Chupp. et Cifferi and
C. vicosae. They also include stem diseases represented by anthracnose of cassava whose symptoms are formed in two stages: (i) wounding by the bug
Pseudotheraptus devastans
(Distant) Het., Coreidae in aprts of the stem that are not yet fully lignified. Wounding activity of
P.devastans is influenced by numerous factors related to the genotype of the insect, the diurnal cycle and environment. Analysis of the results also shows that the saliva of
P. devastans has a toxic or enzymatic effect on the cytoplasm and cell walls of cassava tissues, causing cell degradation; (ii) the wounds are infected by conidia of the fungus
Colletotrichum gloeosporioides
Penz. Among environmental factors, relative humidity plays a major role. Infection of cassava stems under experimental conditions is only successful with high relative humidity close to saturation and at temperatures of 24-28°C. Finally, there are two groups of root diseases referred to as root rots: (i) soft rots caused by
Phytophthora drechsleri
Tuck.,
Pythium
spp,.
Fusarium solani
Mart. and
Sphaerostilbe repens
B. et Br. The latter is the most widespread in the Congo; (ii) dry roots rots caused by
Rigidoporus lignosus
(Klot.) Imazeki,
Rosellinia necatrix
(Hart.) Berk.,
Botriodiplodia theobromae
Pat.,
Armillaria mellea
(Vahn: Fr.) P. Kumm.,
Armillaria heimii
and
Phaeolus manihotis
Heim. Rot caused by
A. heimii is a problem that must be solved in the tropics.
