In this article we will discuss about the wart disease of potato caused by fungi.
Introduction to the Wart Disease of Potato:
The disease, wart disease of potato also known as Black wart of potato, was first described in 1895 from Hungary. Since then it has been reported from the regions of temperate climate like Europe, North America, mountainous areas of South America as well as South Africa.
In India, the disease was first reported from Darjeeling by Ganguly and Paul (1953) and continues to be restricted to that area.
Effect of Wart Disease:
The damage caused by the disease is frequently high since the potato tubers get de- shaped, become tasteless loosing flavour and therefore unfit for human consumption. Young tubers get deformed due to infection and have to be thrown away.
Symptoms of Wart Disease:
The symptoms of the disease appear only on underground parts except roots of the plant i.e. tubers, buds of stems, and stolons. These are characterised by warty, tuberous and dirty Cauliflower like outgrowths on infected parts.
The warty outgrowths vary in size from small protuberances to large intricately branched systems. Early in the growing season they are green or greenish-white in colour if exposed to light but are cream coloured or black on underground parts.
On the tubers, mostly the warts are larger than the tuber itself covering the whole tuber. In advanced stages, the warts become dark black in colour and may sometimes be attacked by saprophytic fungi.
The wart usually consists of distorted proliferated branched structures grown together into a mass of hypertrophied tissue (Fig. 22.1).
The causal organism is Synchytrium endobioticum (Schilb.) Peres.—a holocarpic endoparasite.
The primary infection of the young potato crops available in the field takes place through the germination of resting spores present in the soil into Zoospores.
These zoospores after swimming for a while land on the underground shoot parts, withdraw their flagella and enter the host cells where they settle down at the bottom of the host cells.
Each of the neighbouring cells start dividing repeatedly followed by swelling, ultimately resulting in the formation of wart. There warts are the main Symptoms and contain the material for secondary infection. The sporangia contained in the warts produce zoospores upon disintegration of the hosts.
These zoospores are responsible for secondary infection. If environmental conditions are favourable, the zoospores are formed repeatedly and secondary infections may take place as well causing serious damage to the potato crop.
When the weather conditions become unfavourable and the crop season approaches towards the end, the zoospores function as planogametes, fuse and produce resting sporangia. While the crop is harvested, the resting sporangia remain buried in the soil and perennate waiting for the favourable conditions to return back.
Control Measures of Wart Disease:
It is very difficult to control the disease once it has been introduced in the field.
However, some of the control measures practised are listed below:
(i) Entry of diseased material into healthy areas should be prevented.
(ii) The diseased potato tubers should be discarded.
(iii) Soil treatment may control the disease to a large extent. These include steam sterilisation and application of mercuric chloride—copper sulphate and 5 percent formaline. But these are very costly.
(iv) Cultivation of disease resistant varieties continuously for 8-10 years is the only effective control measure.