The below mentioned article provides a note on puccinia.
The genus includes about 3,000 species. Of these 147 have been reported from India. All are internal parasites attacking angiosperms. Only the spore masses are visible externally.
Some of them such as Puccinia graminis tritici (Black stem rust of wheat) are of great economic importance as they cause destructive rust diseases of major crops such as cereals, millets and other crops.
Many species of Puccinia are autoecious (P. obtegens on thistle). They complete their entire life cycle on a single host species. For instance P. asparagi (D-C) produces all four types of sori on Asparagus, P. major on Crepis paludosa and P. pulverulenta on willow herbs.
There are, however, others which complete their life history on two unrealated hosts much like the malarial parasite. These are known as heteroecious parasites. The best examples of the heteroecious parasites are the wheat rusts.
This peculiar condition of the wheat rusts is known as heteroecism. In India wheat rust disease is caused by three different species of Puccinia.
These are P. graminis, P. striiformis (yellow rust of wheat) and P. recondita (Orange or Brown rust of wheat). P. graminis tritici which is known as the black stem rust of wheat, has been thoroughly investigated. It is usually taken as a type because its life cycle is fully known.
Cultivation of wheat rust in the Laboratory. Since the discovery of heteroecism in rusts by de Barry, all attempts to cultivate the black stem rust of wheat in the laboratory failed.
It was, therefore, considered an obligate parasite. Investigations of Fuchs and Gartner (1958) and Gartner and Fuco (1962) with Uredospores of P. graminis tritici on liquid or solid media resulted in a limited saprophytic growth.
Later Williams et al, (1960) experimented with a race of P. graminis tritici designated 126—ANZ-67. He met with great success. There was unlimited growth from the uredospores.
The hyphae thus produced bore a fresh crop of uredospores. The ingredients of the medium used by Williams et al. were mineral salts, sucrose, 0.1% yeast extract and 1% agar and the pH of the medium was maintained at 6.4.
This experiment showed that the black stem rust of wheat could no longer be considered strictly obligate in its parasitism. Brown (1967) put it in the category of ecologically obligate parasites.
Recendy Bushnell (1976) was able to grow successfully isolates of races 38 and 17 of P. graminis of sp. tritici which had grown poorly on earlier trials on 1% peptone media.
They were grown successfully on media containing higher concentration of peptone combined with an acid hydrolysate of casein.
