Author: Dr. Smita Puri
Sterility mosaic disease (SMD) of pigeon pea was first described in 1931 from Pusa, Bihar State, India and subsequently from the rest of India, and other pigeon pea-growing countries in Asia. However, this disease is not known to occur in Africa or the Americas.
This disease is found all over the India, especially Bihar, Uttar Pradesh, Gujarat, Maharashtra, Tamil Nadu, Andhra Pradesh, Karnataka and Chhattisgarh causing severe loss to the crop.
Economic Importance
The losses caused by this disease are variable and depends on the age of the crop. It has been established that : At <45 days old plants, SMD infection results in 95 to 100% yield loss, while at late plant stage (>45 days old plants) infection depends on the level of infection (i.e., number of affected branches per plant) and range from 26 to 97%. Seeds from partially affected plants are discolored and shriveled, with about 20% reduction in dry weight, and fetch poor price. It is estimated that SMD result in an annual yield loss of over US$300 million in India alone.
Symptoms of the disease
The disease is sometimes referred as “Green Plague” because at flowering time, affected plants remains green with excessive vegetative growth and have no flowers or seed pods. Under suitable conditions, the disease spreads rapidly like a plague, leading to severe epidemics.
Characteristic disease symptoms are complete or partial cessation of flower production (sterility), mosaic or chlorotic ringspot symptoms on leaves, excessive vegetative growth, stunting, and reduction in leaf size.
However, the symptoms of SM vary according to the pigeon pea genotypes and 3 types of symptoms are found.
- • Severe mosaic and sterility
- • Mild mosaic with partial sterility and
- • Chlorotic ring spots without any noticeable sterility.
Symptoms also vary according to the time of infection. Infection in susceptible genotypes at <30 to 45 days old plants results in the expression of characteristic disease symptoms in 10 to 15 days and almost complete cessation of flowering, but leaf symptoms become masked as plants grow. Later infection in susceptible cultivars (>50 to 60 days old plants) results in slightly delayed symptom development and then only mild mosaic symptoms on only a few branches or parts of branches, and such plants show reduced flowering (20 to 50%). However, after rationing or severe pruning, new growth from such plants shows severe mosaic symptoms and complete sterility.
Causal Organism-
Pigeonpea Sterility Mosaic Virus (PPSMV) causes SM disease and it is
a species of the genus Emaravirus. The virus is not sap transmissible but can be transmitted by Eriophyid mite (Aceria cajani) (Acari: Arthropoda) and Grafting. Diseased plants left in fields after harvest, on field banks, or in kitchen gardens, and the presence of perennial pigeonpea or wild relatives of pigeonpea such as C. scarabaeoides serve as primary inoculum sources.
Conducive conditions
- • Crops grown under irrigation or near irrigated fields are the most vulnerable to early SMD infection.
- • Continuous cropping of pigeonpea in the same field.
Control of sterility mosaic disease/mite vector
- • Soil application of phorate 10g @ 1kg ai/ha at sowing + foliar spray with monocrotophos on 30th day after sowing.
- • Seed treatment with aldicarb 10G protected the crop from sterility mosaic for two months under glasshouse conditions.
- • Treatment of seeds or soil with pesticides like carbofuran provided early protection against SMD upto 45 days.
- • Spraying acaricides from early stages of the crop reduces the disease/mite. So, dicofol at 0.05% sprayed 30 and 45 days after sowing recorded least number of vector mites with the lowest disease incidence followed by wettable sulphur 0.2%, monocrotophos 0.04% and ethion 0.1%. Hence an application of dicofol 0.05% was recommended between 30 and 45 days after sowing in endemic areas followed by a repeat application, if necessary after 15 days.
- • Growing resistant varieties such as Bahar, ICPL-151 and Hyd 3C is the most feasible method of disease control.
- • Breaking pigeon pea cycle by crop rotation, changing sowing date etc. is also helpful in reducing the disease severity.
- • Destroying the infected plants during crop season and voluntary diseased plants during the off- season also reduces the sources of primary inoculum.
About Author / Additional Info:
I am a Scientist (Plant Pathology) at JNKVV, Regional Agricultural Research Station, Sagar, M.P.