Diseases of Vegetable, Ornamental and Spice Crops

Exercise 8: DISEASES CAUSED BY RUST FUNGI IN ORNAMENTALS

a) Rust of rose (Causal organism Phragmedium mucronatum (Pers. Ex Pers.), P. fusiformie J. Schrot, P. rosae-pimpinelifoliae Dietel )

Kingdom : Fungi
Phylum : Basidiomycota
Class : Basidiomycetes
Order : Uredinales
Family : Pucciniaceae
Genus : Phragmedium
Species : mucronatum

Symptoms: On upper leaf surface minute, orange pycnia appear. Yellow to brown pustules impart rusty appearance to the shoots. The fungus produces aecial stage in spring. The aecia are prominent as yellowish lesions on the lower surface and the spores get released as the soral membrane fragments following the rupture of the epidermis. They are erumpent, bright orange usually surrounded by a distinct but narrow chlorotic area. Aecia and pycnia also appear on petioles and young woody stems. After aeciospores infect the leaves, the uredinial stage starts forming as a whitish fleck on the lower surface of the lesion. Mature uredinia are reddish, orbicular-shaped and contain orange coloured urediniospores which are released about 14 days after the leaf become infected. These spores continue to cause new infections throughout the summer.

Uredinia: Reddish, orbicular-shaped and contain orange coloured urediniospores.


b) Rust of jasmine (Causal organism Uromyces hobsoni Vize.)

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

Symptoms: The fungus attacks leaves, stem and inflorescences. Leaves show the presence of orange coloured aecial cups on both sides, but predominantly on the lower surfaces.The fructification or sori are formed on the thickened portions.The sori are initially yellow owing to their contents, the aeciospores later turn darker due to formation of teliospores.

Aecia and Aeciospores: Aecia are raised, scattered ,orange-coloured, aecidioid and aeciospores are orange-yellow, thin-walled, 16.5-21 x12-18?m in size.

Uredinia and Urediniospores: Uredinia measures 40-26 µm, The urediniospores are round to ovate, lifht brown echinulate, with -4 equatorial germ pores and measures 20-30 x 18-26 µm.

Teleutospores: The teleutospores are dark brown, one celled, mostly ovate, thick-walled, 35-45x20-30 µm in size and pedicel is hyaline or yellow in colour.


c) Rust of geranium (Causal organism Puccinia pelargonii-zonalis Doidge)

Kingdom : Fungi
Phylum : Basidiomycota
Class : Basidiomycetes
Order : Uredinales
Family : Pucciniaceae
Genus : Puccinia
Species : pelargonii-zonalis

Symptoms: The typical symptoms of the disease are white flecks, pinhead size usually on the upper surface of leaves while directly beneath these white flecks on the lower surface of the leaves are found small, white or chlorotic blister-like pustules. As the chlorotic spots enlarge, the pustules in the centre enlarge, erupt and become reddish brown with spores. Uredia are then observed in a more or less circular fashion around the original sorus. Most rust spots are formed on the lower surface of the leaves although they occasionally form on the upper surface. Heavily infected leaves turn chlorotic and defoliate.The spots are more apparent on leaves but also may develop on petioles, stipules and stems.

Uredospores: The fungus produces subglobose to ovate, light brown uredospores measuring 24.5x22.0µm, thin echinulated with two equatorial germ pores

Teliospores: Telial stage is comparatively very rare. The fungus is microcyclic; teliospores are 36-50 x 16-24 µm in size.