Diagnostic Notes
Symptoms
The disease commonly occurs on adult plants from the beginning of the yield. The first symptom is a slight wilt of the branch tips, followed by sudden death of the plant within 4 – 14 days. Before the wilt of the whole plant, a partial wilt (one side of the plant) can occurs. Usually, the wilted leaves do not turn yellow and are still attached to plant for a few days. At the same time, occurs upward internal darkness from the stem base up to around 1m, root rot and even cracks at the stem base. When there is high humidity, the fungus can produce conidia at the stem base. Due it is caused by a soilborne fungus, the disease starts in localized areas in the field and its dispersal is somewhat aggregated.
The Fungus
F. oxysporum Schltdl. emend. W.C. Snyder & H.N. Hansen produces hyaline, oval to kidney-shaped, generally single-celled microconidia in false heads. Macroconidia are hyaline, slightly sickle-shaped, and thin-whaled, with an attenuated apical cell and a foot-shaped basal cell. Conidiophores are monophialides. Chlamydospores are formed singly or in pairs, profusely in culture. The teleomorph is unknown (Nelson et al. 1983).
Identification
Whereas there are a huge number of non-pathogenic or saprophytic strains of F. oxysporum, especially in soil, and they cannot be differentiated among themselves and from the tens of formae specialis of pathogenic F. oxysporum, then to make a sure diagnosis, it is necessary to isolate the fungus from the leading edge of lesion on cuts through the lumen of the stem and, afterwards, carry a Koch’s postulates.