The fungus infects chickpeas via the roots and moves throughout the host’s vascular system. Cell wall degrading enzymes produced by the pathogen break down the host cell walls to form gels that block the plant’s transport systems and cause yellowing and wilting symptoms. Vascular discolouration occurs from the roots to the young stems, followed by a yellowing and wilting of the leaves before final necrosis (Brayford 1998, Leslie & Summerell 2006).
Affected seedlings can be identified approximately 3 weeks after sowing and show symptoms such as drooping and paler coloured leaves. The young plants will collapse to a prostrate position. These seedlings usually have shrunken stems above and below soil level. There are no superficial signs of rotting, but when roots are split longitudinally there is a brown to black discolouration of internal tissue (Nene et al. 1978 & Haware et al. 1986).
Adult plants experience wilting symptoms which progress from petioles and younger leaflets in 2 to 3 days to the whole plant. Lower, older leaves develop chlorotic symptoms whilst higher leaves stay a dull green; with progression of the disease all leaves turn yellow. Discolouration of internal tissue (pith and xylem) occurs in the roots and can be seen when dissected longitudinally (Nene et al. 1978 & Haware et al. 1986).
Fusarium oxysporum Schltdl. emend. W.C. Snyder & H.N. Hansen is a common soil inhabitant and produces three types of hyaline asexual spores: a) Macroconidia are usually 3–5-septate, straight to slightly curved, relatively slender and thin-walled, with a foot-shaped to pointed basal cell and a tapered and curved, sometimes with a slight hook, apical cell, 25–65 × 3.5–4.5 µm (Haware et al. 1986). They are produced abundantly on pale orange sporodochia and occasionally from hyphae growing on the agar surface. In some isolates, sporodochia may be sparse or non-existent; b) Microconidia are usually unicellular, oval, elliptical or kidney-shaped, produced
There is a large number of non-pathogenic or saprophytic strains of F. oxysporum
Seed health tests and seedling symptoms tests can be found in Haware et al. (1986).