Diseases of Vegetable, Ornamental and Spice Crops

Exercise 11: DISEASES CAUSED BY COLLETOTRICHUM SPP

a) Anthracnose of French bean (Causal organism Colletotrichum lindemuthianum (Sacc. and Magn.)

Kingdom : Fungi
Phylum : Deutromycota
Class : Coeleomycetes
Order : Melanconiales
Family : Melanconiaceae
Genus : Colletotrichum
Species : lindemuthianum

Symptoms: The initial symptom includes dark brown to black lesion along the leaf veins on the underside of the leaves. On pods, the spots appear as circular, Reddish-brown to near black sunken lesions with light or gray centers are seen on pods.

Mycelium: Mycelium branched, septate and hyaline at first becoming dark coloured with age.

Asexual reproduction: In acervulus, setae occur sparingly. Conidia are borne acrogenously on short conidiophores (Fig. 1). Conidia are hyaline, cylindrical with rounded ends or somewhat pointed at one end. A clear vacuole like body often occurs near the center.
Sexual reproduction: Perithecia contain hyaline and filiform periphyses and asci. Each ascus contains eight ascospores, which may be alantoid in shape. Ascospores are ejected from the tip of ascus.

Fig. 1: Acervulus of Colletotrichum lindemuthianum

b) Die-back and anthracnose of bell pepper/ chillies (Causal organism Colletotrichum capsici (Syd.) Butler and Bisby)

Kingdom : Fungi
Phyllum : Deutromycota
Class : Coeleomycetes
Order : Melanconiales
Family : Melanconiaceae
Genus : Colletotrichum
Species : capsici

Symptoms: Branches show die-back symptoms and become straw coloured. Fruits turning red are most susceptible to this disease. Fruits have dark sunken spots alongwith pink areas of fungal fructifications.

Mycelium: Mycelium septate, intercellular as well as intracellular and aerial mycelium appears light to dark grey in colour.

Asexual reproduction: Acervuli are round and elongated in shape. Setae are scattered, brown, 1-5 septate, rigid and swollen at base and acute at apex. Conidiophores are short, hyaline to faintly brown, cylindrical, septate or aseptate (Fig. 2a). Conidia are falcate, fusiform with acute apices and narrow truncate base (Fig. 2b). They are one celled, hyaline and uninucleate.

Sexual Reproduction: Perithecia contain hyaline and filiform periphyses and asci. Each ascus contains eight ascospores, which may be alantoid in shape. Ascospores are ejected from the tip of ascus.

Fig. 2a: Acervulus of Colletotrichum capsici b: Different shapes of conidia

c) Anthracnose of cucurbits (Causal organism Colletotrichum orbiculare (Berk. and Mont.)

Kingdom : Fungi
Phylum : Deutromycota
Class : Coeleomycetes
Order : Melanconiales
Family : Melanconiaceae
Genus : Colletotrichum
Species : orbiculare

Symptoms: Disease symptoms vary on various hosts and also on different parts of the same host. On leaves the lesions are rough, circular, light brown to reddish brown in colour. The spots on fruits are roughly circular, sunken, water-soaked with dark borders and of considerable size. Old spots turn black and are covered with pink spore masses especially in moist weather.

Mycelium: Mycelium septate, intercellular as well as intracellular and aerial mycelium appears light to dark grey in colour.

Asexual reproduction: The fungus produces black stromata bearing black setae and hyaline conidiophores on the host surface. Conidia are one celled, hyaline oblong to ovate and are disseminated by water.

Sexual reproduction: Perithecia contain hyaline and filiform periphyses and asci. Each ascus contains eight ascospores, which may be alantoid in shape. Ascospores are ejected from the tip of ascus.