Blacl scurf disease of potato
Which is the causal organism of Black scurf disease of Potato?
It is caused by a fungus called Rhizoctonia solani
What are the symptoms of Black scurf?
At the time of sprouting dark brown colour appear on the eyes.
Affected Xylem tissue causes to wilting of plants.
Infected tuber contains russeting of the skin.
Hard dry rot with browning on internal tissue. Spongy mass appear on the infected tuber.
Seed tubers are source of spread.
Moderately cool, wet weather and temp 23 °C are the favourable for the development of disease.
What are the characteristics of Pathogen causing Black scurf?
The mycelium is hyaline when young and brown at maturity.
Hyphae are septate and branched with a characteristic constriction at their junction with the main hyphae.
The branches arise at a right angle to main axis. Sclerotia are black.
A basidium bears four sterimata each with a basidiospore at the end.
The basidiospores are hyaline, elliptical to obovate and thin walled.
They are capable of forming secondary basidiospores.
What is the Mode of spread and survival of pathogen?
The fungus is capable of leading a saprophytic life on the organic material and can remain viable in the soil for several years.
The sclerotia on the seed tubers is the principal source of infection of the subsequent crop raised with these tubers.
On return of favourable conditions the mycelium present in the soil may develop producing new hypae.
What are the control measures of black scurf dusease?
Disease free seed tubers alone should be planted.
If there is a slight infection of black scurf that can be controlled by treating seed tubers with mercuric chloride solution for 1.5 hr with acidulated mercuric chloride solution for 5 min.
Treating the soil with pentachloroni trobenzene at the rate of 70 kg/ ha lowers the incidence of the disease, but it is too expensive and cumbersome.
Well sporulated tubrs may be planted shallow to control disease.
The disease severity is reduced in the land is left fallow for 2 years.
Further readings and references