Diseases of Vegetable, Ornamental and Spice Crops

Exercise 7: DISEASES CAUSED BY RUST FUNGI

a) Rust of peas (Causal organism Uromyces fabae (Pers.) de bary )

Kingdom : Fungi
Phylum : Basidiomycota
Class : Basidiomycetes
Order : Uredinales
Family : Pucciniaceae
Genus : Uromyces
Species : fabae

Symptoms: Rust pustules first become evident as minute, raised pustules, which later become distinct, yellowish and circular. The yellow spots have aecia and persist for longer time. The uredo pustules develop on both surfaces of the leaves as well as on other parts and give light brown powdery appearance to the plants in case of severe infections. Late in the season, teleuto pustules also develop on the leaves but most commonly on stems and petioles. They are dark brown or almost black in colour.

Mycelium: Mono and dikaryotic, septate, branched, developed, intercellular with haustoria.

Spermogonia: Not very common, however, flask shaped ostiolate, contains numerous spermatia and receptive hyphae (Fig. 1).

Aecia: Short, whitish and cupshaped, aeciospores round, elliptical, yellow in colour and warty (Fig. 1).

Uredinia: Round, light brown, appear on both surfaces, urediniospores round, ovate, light brown and warty (Fig. 1).

Telia: Formed on leaves, stem and petioles, round, dark brown in colour, contain numerous sub-globose or ovate with rounded or flattened apex which is thick, smooth walled and brown (Fig. 1).

Fig. 1: Microscopic details of Uromyces fabae

b) Rust of large cardemom (Causal organism Phakopsora elettariae (Racib.) Cummins)

Kingdom : Fungi
Phylum : Basidiomycota
Class : Basidiomycetes
Order : Uredinales
Family : Pucciniaceae
Genus : Phakopsora
Species : elettariae

Symptoms: The disease is mostly observed during May and June on the lower surface of leaves in the form of minute, brown uredosori. The numerous uredosori are surrounded by chlorotic halos during early stages of development. In severe cases, the whole leaf gets covered by uredosori resulting in premature drying.