Fungal diseases of Blackgram and Greengram in India and their Control Measures
Authors: Dinesh Chand, Pardeep Kumar*, Jameel Akhtar*, Nilamani Dikshit and M. Abdul Nizar
ICAR-National Bureau of Plant Genetic Resources, Regional Station, Akola-444104, Maharashtra
*ICAR-National Bureau of Plant Genetic Resources, Pusa Campus, New Delhi-110012

Blackgram [Vigna mungo (L.) Hepper] and greengram [V. radiata (L.) R. Wilczek] belonging to the family Fabaceae are important pulse crops in India. From ancient times both the crops have played a very important role in human diet in India as a rich source of protein. India is one of the principal pulse growing country in the world with an area of about 23.9 million hectares and with an average production of 15.8 million metric tons per year. Despite growing pulses in a large area, the production and average yield/ hectare are very low (661 kg/ha) (Singh, 2011). In contrast, in France pulses are grown in only about 4.68 million hectares but the production is 20.79 million metric tons with an average yield of 4444 Kg/ hectares. About 88% of proteins consumed in India are of vegetable origin and pulses contribute about 17-43 % of vegetable proteins, aid in supplementing cereal based diet of the large vegetarian population in the country. Also, they serve as good forage and grain concentrates in cattle food.

The cultivation of blackgram and greengram is comparatively restricted to tropical regions. Blackgram is an important grain legume in India, Pakistan, Myanmar, and some parts of South East Asia, parts of Africa and America. Greengram is cultivated in Africa, China, Fiji, India, Myanmar, Pakistan and Sri Lanka. In India, these are grown in Andhra Pradesh, Bihar, Gujarat, Jharkhand, Karnataka, Madhya Pradesh, Maharashtra, Punjab, Rajasthan, Tamil Nadu, Uttaranchal, Uttar Pradesh, Odisha and West Bengal. In North India these crops are mainly grown in Kharif season, where as in other parts of the country it can be grown in all the seasons. During the Rabi season, the crop is cultivated mainly in Andhra Pradesh, Bihar, Madhya Pradesh, and Odisha. It is also grown as a summer crop in sub-mountain regions and outer ranges of northwest Himalayas up to an altitude of 2000 meter above sea level.

One of the major constraints in achieving the potential yield of pulses in India is the occurrence of various diseases and pests. A large number of fungi, viruses, several insects and nematodes have been recorded which affect production. Since blackgram and green- gram have common diseases, these have been dealt with together. The description of some important fungal diseases, their symptoms, causal organism, epidemiology and control measures are mentioned below.

Anthracnose:

The production of these two major Kharif pulses (blackgram and greengram) is adversely affected by several biotic stresses. Among biotic stresses, fungal foliar diseases especially five species of Anthracnose, have emerged as the most important ones causing immense loss in farmer’s field. The disease anthracnose caused by Colletotrichum spp. occurs in epiphytotic condition on several legumes including blackgram and greengram. The disease appears especially on aerial parts at any stage of plant growth. The chief characteristic symptoms of infected plants showed circular, dark brown spots and bright red orange margins appear on leaves and pods. The infection may also develop as small brown spots, which enlarge and then turn dark brown to black, where dark coloured spots are visible. Later these spots increase in size by developing concentric ridges. In severe infections, the affected parts wither-off. After infection, germination of seeds causes blighting of the seedlings. It is dangerous disease and the severe infection reduces the plant growth and the affected plant die. It has been reported in different states of India.

Control measure:

  1. Remove and destroy infected plant debris from soil.
  2. Avoid growing fresh crop in the infected field.
  3. Seed treatment with Thiram or Captan @ 2 to 3 g per kg.
  4. Spray Dithane M-45 @ 2kg in 1000 litres of water per hectare.


Charcol Rot:

Charcol rot caused by Macrophomina phaseolina is a serious pathogen of many crops including blackgram and greengram. There are more than 500 hosts of the fungus including legume and cereal plants (Sinclair, 1982). M. phaseolina is a soil and seed-borne pathogenic fungus and produces cushion shaped black sclerotia. It causes root rot, collar rot, stem rot, leaf blight, pod and seed infection in blackgram and greengram in different parts of the country. An early sign of stem infection is the presence of brown lesions at the base of the plant and where the branches join the main stem and ultimately the stem turn ashy-grey, often with small black minute (microsclerotia) within the affected area. Infected plants usually die prematurely. Yield can be significantly reduced. It generally occurs after flowering during a period of heat/ moisture stress, and results from infection of the roots by soil-borne microsclerotia. High temperature and moderately wet weather conditions favour disease. In soil, maximum growth of the fungus occurs at 30 ˚C and 15% moisture. Disease severity increases with the increasing in temperature with optimum at 30-35˚C (Grover and Sakhuja, 1981).

Control measure:

  1. Resistant varieties are the best means for controlling the disease.
  2. Planting on good soil moisture, and standard agronomic practices to minimize stress, can reduce the risk from charcoal rot.
  3. Agallol, Captan and Thiram are effective in controlling the seed-borne infection and promoting the germination of seeds.
  4. Carbendazim, thiophanate-methyl and benomyl gave more than 90% control of foliage blight when applied as foliage treatments.


Cercospora Leaf Spot:

This is an important disease of blackgram and greengram and is usually occurs in severe form, causing heavy losses in yield. Cercospora leaf spots was first known to occur in Delhi, India and is prevalent in all parts of the humid tropical areas of India, Bangladesh, Indoneasia, Malaysia, Philippines, Taiwan as well as Thailand. It becomes severe in the wet season causing up to 100% yield loss. Cercospora leaf spot causes leaf spotting and defoliation on pulses in warm and humid climates of the country.

In India, the disease occurs mostly in blackgram and greengram growing states particularly in Assam, Bihar, Haryana, Himachal Pradesh, Madhya Pradesh, Maharashtra, Odisha, Punjab, Rajasthan and Uttar Pradesh. It is common in Bihar, Haryana, Punjab and Uttar Pradesh. The symptoms produced by Cercospora spp. may be influenced by several factors and are generally characterized by the appearance of leaf spot that are circular and / or irregular in shape with grayish- white centres and reddish brown to dark brown margins are visible on the leaves. The spots may increase in numbers and size during flowering and pod formation stage, when environmental conditions are favorable for this spread. The leaf spot disease caused by Cercospora canescens Ellis. & Martin, infects blackgram and greengram producing typical leaf spots around flowering stage. The spots appear 3-5 weeks after sowing of the crops, depending upon favourable conditions, particularly day and night temperature and relative humidity. The symptoms on leaves and fruits in both the crops may vary depending on the isolate of fungus and host variety. The disease is most prevalent during the rainy season. High humidity favours disease development and also depend upon the causal agent and host. High disease severity is observed on early sown blackgram crop at the flowering stage. Cercospora leaf of mungbean can be controlled by spraying Bavistin.

Control measure:

  1. Use seeds from the disease free crops.
  2. Mulching reduces the disease incidence resulting in increased yield.
  3. Maintain low crop population density and wide row planting.
  4. Spray Dithane M-45 or Dithane Z-78 @ 2 kg in 1000 litres of water per hectare.


Powdery Mildew:

Powdery mildew (Erysiphe polygoni DC.) is an important disease of plants and known to occur in all parts of the world. It is one of the widespread diseases of many legumes. The disease is noticed generally on all aerial parts of the plants and is one of the major constraints in the production of blackgram and greengram which cause both qualitative and quantitative loss of grains. However, disease intensity depends upon the cultivar, growing period and environmental conditions. The disease has world â€"wide importance, occurring wherever it is grown, particularly in the Indian sub-continent and Southeast-Asian countries. In India and Southeast Asian countries it becomes severe in dry season causing up to 50% yield loss. Temperature and humidity favours the rapid spread in susceptible varieties. The powdery mildew occurs throughout the year under favorable conditions and can cause significant damage to late sown Kharif crops.

The infected plants appear a grayish- white powdery growth on the surface of leaves, stem and pods and other green parts which later become dull coloured. In the early stage of infection, light yellowish, irregular spots appear on the leaves, which rapidly turn brown. Initial symptoms are marked by faint, slightly dark areas on the leaves. These areas develop into small, white powdery spots. Severely affected parts of the plants get shriveled and distorted. Dry weather, temperature and relative humidity favours the disease. Powdery mildew occurs under cool temperature (18 ˚C to 20 ˚C) and is favoured by cloudy weather. Significant yield loss can occur if powdery mildew develops before or at flowering, particularly if the crop is under moisture stress.

Control measure:

  1. The seeds sown early in the month of June to avoid early incidence of the disease on the crops.
  2. Use of resistant varieties.
  3. Foliar sprays with a registered fungicide, or one under permit, is warranted where infection occurs at or prior to flowering. Khosla et. al. (1988) found effective control with Bavistin, Bayleton, Calixin, Karathane and Microsulf in both blackgram and greengram.


Rhizoctonia Root Rot (Web Blight):

Web blight of blackgram and greengram caused by Thanatephorus cucumeris (Frank) Donk (Rhizoctonia solani Kuhn) is seed and soil-borne disease. Rhizoctonia solani (Kuhn) first reported from Kanpur, India, is responsible for significant yield loss in blackgram and greengram. Rhizoctonia disease is wide spread and reported on blackgram and greengram in India, Taiwan, Iran, Phillipines and West Malaysia.

The disease symptoms start initially with yellowing and drooping of the leaves. The fungus produces dark brown, septate mycelium with narrowing at hyphal branches. The symptom produces by this fungus as reddish brown, sunken lesions on the seedlings. These lesions may become enlarge, fuse together, and ultimately the affected seedlings collapse and die. The affected plants can be easily pulled out due to rotten root portions in the ground. The infected plants may be seen in small patches or scattered over the entire field. The development of the disease is favoured by day temperature around 30 ˚C and prolonged dry season followed by irrigation.

Control measure:

  1. Single soil drench with thiophanate-methyl and twice with benomyl gave 90% disease control.
  2. Treat the seeds with Carbendazim + Thiram @ 2g/ kg.
  3. Crop rotation, adjusting time of planting to avoid periods of low temperature and draining wet areas of the field.
  4. Apply farm yard manure or green leaf manure (Giricidia maculate) at 10 t/ha or neem cake at 150 kg/ha.


Rust:

The rust disease occurs on blackgram and greengram is a major thrust to successful cultivation. It is usually present on greengram in the rainy season. The rust has been reported on blackgram and greengram from India. The disease symptoms look like circular, reddish-brown pustules which appear more commonly on the lower side of the leaves. The disease is rare on pods and can be seen on stems. Severely infected leaves become shriveling followed by defoliation. The rust is caused by (Uromyces appendiculatus (Pers.) LK. It is an autoecious long cycle rust and all the spore stages occur on the same host. The pathogen survives on other legume hosts. Cool and moderate temperature favours the disease. The temperature ranges of 21-26 ˚C, nights with heavy dew, moisture on the leaf surface and high relative humidity favour infection and for further disease development.

Control measure:

  1. Removal of the infected plant debris and destroy is important to decrease the severity of diseases.
  2. Adjustment in time and date of sowing may help in reducing the disease
  3. Use of tolerant varieties is best way to prevent the onset of diseases.
  4. fungicidal application such as Calaixin (0.07%), followed by Baycor (0.1%) and Bayleton (0.2%) gives the best result to manage rust in mungbean.
From the above account on symptoms, causal organism, epidemiology, disease cycle and control measure of the pathogens, it is amply clear that all the fungal diseases of blackgram and greengram are economically important that may cause appreciable seed yield loss. It is prevalent almost throughout the country on these crops. The level of severity in both the crops is known as quite high depending upon the temperature, humidity and cultivar which highlights the need for quality control of seeds through seed certification programme.

Sources of resistance have been found in both blackgram and greengram for developing resistant varieties which need to be confirmed by multi-location testing which would enable testing different geographical isolates.

The contributions made during the present studies provided critical inputs for developing efficient management strategy for these diseases through quality control of seeds and crop improvement programme of blackgram and greengram.

References:

• Grover, R.K. and Sakhuja, P.K. 1981. Some pathological studies on Rhizoctonia bataticola leaf blight of mungbean. Indian Phytopath. 34: 24-29.
• Khosla, H.K., Naik, S.L., Mandloi, S.C. and Goray, S.C. 1988. Control of powdery mildew of mung and urd in relation to losses and disease development. Indian Phytopath. 41: 59-63.
• Sinclair, J.B. 1982. Compendium of Soybean Diseases, American Phytopathological Society, Saint Paul, Minn, USA, 2nd edition.
• Singh, R.P. 2011. Directorate of Pulses Development, Department of Agriculture & Co-operation (Ministry of Agriculture, Vindhyachal Bhavan, Bhopal-462004, Madhya Pradesh.

About Author / Additional Info:
Scientist, Plant Quarantine Division, ICAR- National Bureau of Plant Genetic Resources, Pusa Campus, New Delhi- 110 012