Canna Rust

The online "New Disease Reports" published an article on 2nd December 2002, in which they reported the discovery of a previously unknown disease that affects Canna. During December, 2002, Canna edulis plants at the Central Tuber Crops Research Institute, Kerala, India, were found to be infected with a rust fungus.

Figure 1. Lower surface of an infected canna leaf

The pathogen produced numerous small yellow powdery pustules, primarily on the lower surface of the infected leaves (Fig. 1) and a corresponding small yellowish lesions of 1-2 mm diameter were seen on the upper surface (Fig. 2). In advanced stages of infection, the upper leaf-surface spots coalesce, turn dark brown-to-black and finally the infected leaves become dry and fall.

Figure 2. Upper surface of an infected canna leaf

Microscopic observations revealed the uredinospore rust stage. Uredinia were hypophyllous, subepidermal, erumpent, dark yellowish, circular to irregular in shape. Urediniospores were light yellow in colour round to ovate in shape, echinulate and 25-35 µm x 15-20 µm include wall thickness. The pathogen was identified as Puccinia thaliae (HCIO. NO. 44.744). A reference sample has been deposited in the Herbarium of the Indian Agricultural Research Institute, New Delhi.

This is the first record of P. thaliae infecting C. edulis in India. Literature searches show that there are no previous records of this disease from India (Bilgrami et al, 1991; Butler, 1997). Bagyanarayana & Ramesh (1999) reported Puccinia cannacearum, another rust fungus on Canna indica from India. The only previous report of P. thaliae infecting canna is from Hawaii on Canna indica (Gardner & Hodges, 1989).