Diseases of Vegetable, Ornamental and Spice Crops

Exercise 9: DISEASES CAUSED BY FUSARIUM SPP.

a) Fusarium wilt of pea (Causal organism Fusarium oxysporum Schlechtend ex Fr. f. sp. pisi (J.C.Hall) Snyder and Hansen)

Kingdom : Fungi
Phyllum : Ascomycota
Class : Deuteromycetes
Order : Moniliales
Family : Tuberculariaceae
Genus : Fusarium
Species : oxysporum
f.sp. : pisi

Symptoms: Initial symptoms are usually yellowing of the lower leaves. The stems at or near the soil line may be slightly thickened and brittle. A cross section of the lower stem often reveals a lemon to orange –brown and finally black discoloration of xylem vessels. Affected plants may wilt and die either slowly or rapidly. The disease generally occurs in patches in the field.

Mycelium: Septate, branched, hyaline, inter or intracellular (Fig.1 a).

Asexual: The fungus produces two types of spores i.e. micro and macro conidia.

Micro conidia: The conidia are ellipsoidal, straight to curved, 0 to 1 celled and hyaline.

Macro conidia: The conidia are typically fusiform, hyaline and multiseptate.

Chalamydospores: The chlamydospores are small, rough and formed terminally or intercalary (Fig. 1b).

Fig. 1a: Mycelium of Fuasrium oxysporum f.sp. pisi b: Chlamydospores of Fusarium oxysporum

b) Fusarium wilt of okra (Causal organism Fusarium oxysporum Schl. ex Fr. f. sp. vasinfectum (Atkinson) Snyder and Hansen)

Kingdom : Fungi
Phyllum : Ascomycota
Class : Deuteromycetes
Order : Moniliales
Family : Tuberculariaceae
Genus : Fusarium
Species : oxysporum
f.sp. : vasinfectum

Symptoms: The characteristic symptoms of the disease appear as yellowing and stunting of the plants followed by wilting and rolling of the leaves. Finally the plant dies. Vascular bundles of the affected plants appear as dark streaks. The whole stem is blackened in case of severe attack.

Mycelium: Septate, branched, hyaline, intracellular.

Asexual: The fungus produces two types of spores i.e. micro and macro conidia.

Micro conidia: The conidia are ellipsoidal, straight to curved, 0 to 1 celled and hyaline (Fig. 2c).

Macro conidia: The conidia are typically fusiform, appear buff to salmon orange in colour and 3 septate (Fig. 2b).

Chlamydospores: Both intercalary and terminal and are broadly ovate (Fig. 2d).

Fig. 2: Microscopic details of Fusarium oxysporum f. sp. vasinfectum

c) Yellows of ginger (Causal organism Fusarium oxysporum Schl. f.sp. zingiberi Trujillo)

Kingdom : Fungi
Phylum : Ascomycota
Class : Deuteromycetes
Order : Moniliales
Family : Tuberculariaceae
Genus : Fusarium
Species : oxysporum
f.sp. : zingiberi

Symptoms: Plants show drooping, wilting and drying. Disease appears in patches. Cortical rot prominent in rhizomes. Roots show decaying effect.

Mycelium: Mycelium delicate, white or peach usually with a purple tinge.

Asexual reproduction: Microconidia borne on simple phialides. They are abundant straight to curved, oval-ellipsoidal cylindrical. Macroconidia sparse generally 3-5 septate, falcate with pedicellate base.

Sexual reproduction: Perithecia sometimes formed. Chlamydospores abundant.