Pearl Millet

Description

Pearl millet, Pennisetum glaucum, is an annual grass in the family Poaceae which is grown widely in Africa and India for its grain which can be used to make flour and other foodstuffs. Pearl millet is a very robust grass which tillers widely and grows in tufts. It has slender stems which are divided into distinct nodes. The leaves of the plant are linear or lance-like, possess small teeth and can grow up to 1 m (3.3 ft) in length. The inflorescence of the plant is a spike-like panicle, made up of many smaller spikelets where the grain is produced. Pearl millet can reach 0.5 to 4 m (1.6–13.1 ft) in height depending on the cultivar and is an annual plant, harvested after one growing season. Pearl millet may also be referred to as bulrush millet, cat-tail millet or yellow bristle grass and originates from the Sahel zone of Africa.

Synonyms are P. americanum (L.) Leeke, and P. typhoides (Burm.) Stapf. & Hubb.) And common names include bullrush millet, cat-tail-millet, mil-a-chandelle, bajra, kambu, duhkn.


Uses

Pearl millet grain can be ground into flour and used to produce porridge, or a type of flat bread. It can also be cooked and prepared in a manner similar to couscous or rice. The plant stems can be used for roof thatch and building construction. In countries other than Africa and India it is most widely grown as fodder.


Propagation


Basic requirements
Pearl millet is adapted for growth in dry conditions where there is low rainfall. It is a warm season crop which will produce tillers at temperatures of 21–24°C (69.8–75.2°F) and develop spikelets at the slightly higher temperature of 25°C (77°F). Pearl millet is tolerant of a variety of soils, including acidic and sandy soils and those which are nutrient poor but it will not tolerate waterlogging. The plants will grow optimally in a well-draining, fertile soils with a pH between 6.0 and 7.0.

Propagation
Pearl millet is propagated directly from seed. Pearl millet seed is usually sown directly on fields on hills or ridges with short lived cultivars being planted as soon as possible after the wet season in semi-tropical regions. A well-prepared seedbed is important to ensure rapid development of seedlings. Pearl millet seeds are best sown when the soil has warmed to at least 20°C (68°F). Seed can be sown in furrows if the soil is light or if the plant is being grown in drier areas, or by broadcasting. Seeding rates vary from 12–15 lb of seed per acre when using a seed drill, to 30–40 lb per acre when seed is broadcast. A distance of 45–60 cm (17.7–23.6 in) is usually allowed between rows.

General care and maintenance
Pearl millet is a fast growing crop that will quickly be able to outcompete weeds. It is, however, important to maintain a weed-free seed-bed as young seedlings are susceptible to competition. Traditional cultivation of pearl millet in Africa relies on rainfall to irrigate the plants and involves the application of little to no nitrogen fertilizers. The reason for this is often the application of nitrogen promoted vigorous early growth that can result in the plants using up water required at later stages of growth. In more temperate regions where pearl millet is grown as a forage crop, fertilizer application should be based on the results of a soil test.

Harvesting
Pearl millet reaches maturity between 50 and 180 days after planting, depending on the variety. The crop is harvested by hand either by cutting the spikes from the plant or by cuting the whole plant.



References

CABI Crop Protection Compendium. (2008). Pennisetum glaucum (pearl millet) datasheet. Available at: http://www.cabi.org/cpc/datasheet/39766. [Accessed 25 March 15]. Paid subscription required.

Myers, R. L. (1999). Pearl millet. Alternative crop guide. The Jefferson Institute. Available at: https://www.hort.purdue.edu/newcrop/a.... [Accessed 25 March 15]. Free to access.

Newman, Y., Jennings, E., Vendramini, J. & Blout, A. Pearl millet (Pennisetum glaucum): overview and management. University of Florida IFAS Extension. Available at: http://edis.ifas.ufl.edu/pdffiles/AG/.... [Accessed 25 March 15]. Free to access.

Thakur, R.P., Subba Rao, K.V. & Williams R.J. 1983. Effects of pollination on smut development in pearl millet. Plant Pathology 32, 141 - 144.

Thakur, R.P., Subba Rao, K.V. & Williams R.J., et al. 1985. Identification of stable resistance to smut in pearl millet. Plant Disease 70, 38 - 41.

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Curation
This page is curated by Dr Robert J Williams who led the pearl millet pathology program at ICRISAT from 1975 thru 1982, working on the diseases of this crop in India and the African Sahel. Prior to ICRISAT, Dr Williams led the grain legume pathology program at IITA in west Africa from 1969 to 1975, and at IITA also worked on cassava and rice diseases. Dr Williams has published much of that research in Phytopathology, Plant Disease, and various other journals.

In 1984 Dr Williams published a comprehensive review of Downy Mildews of Tropical Cereals in Advances of Plant Pathology Volume 2, pp 1 - 103.

Dr Williams has assembled a large collection of diagnostic photographs of diseases of tropical food crops and has donated many of these together with critical descriptors to Cornell University's Department of Plant Pathology & Plant-Microbe Biology working there with Dr Kathie Hodge. The collection, titled Robert J Williams Photograph Collection, can be accessed via: http://www.plantpath.cornell.edu/CUPp...

Dr Williams has retired to a smallholding in west Wales, growing fruit and veg, where he also writes content for PlantVillage, sharing his valuable knowledge.



Common Pests and Diseases

Rust
Puccinia substriata

Symptoms
Small yellow or white raised spots on upper and lower leaf surfaces; spots tend to be more numerous on lower leaf surface; spots enlarge and develop into red-brown pustules which may be surrounded by a yellow halo.
Cause
Fungus
Comments
Spores can be spread via wind and survive in crop debris in the soil.
Management
Plant resistant varieties of millet if rust is a persistent problem; avoid the use of overhead irrigation; do now plant millet in close proximity to eggplant or other Solanaceous crops; there are no recommended chemical controls for rust.

Cercospora leaf spot
Cercospora penniseti

Symptoms
Small dark lesions on leaves which are usually oval in shape but may be oblong to rectangular; centers of lesions are gray to tan in color with visible black dots; lesions may be covered in spores during wet weather; lesions may also be present on the stems and are slightly longer than those on the leaves.
Cause
Fungus
Comments
Disease emergence occurs when high temperatures coincide with periods of high humidity.
Management
Avoid planting millet varieties that are highly susceptible to Cercospora fungi; control weeds in field; rotate crops and practice good sanitation; no chemical control is needed to treat the disease.

Ergot
Claviceps fusiformis

Symptoms
Ergot is a disease of pearl millet grain-bearing heads (inflorescences). The first sign of ergot infection in pearl millet is the appearance of viscous creamy-pink exudations, called honeydew on the flowering heads. Subsequently hard brown spiky structures are formed, called sclerotia.
Cause
Fungus
Comments
Ergot reduces grain yields and constitutes a health hazard to humans and animals that consume pearl millet products contaminated with the alkaloid-containing sclerotia of the causal fungus. It is a particularly serious disease of pearl millet F1 hybrids.

Biology and Epidemiology: Infection of the individual florets on a pearl millet inflorescence occurs via the stigmas, i.e. the white feathery structures through which the florets are fertilised following pollination. Initial infection is from spores (ascospores) produced from sclerotia in the soil or in crop debris. Secondary infection is from the spores (conidia) produced in the honeydew. Once the stigmas have been pollinated they rapidly wither and are no longer available as the infection route for the ergot fungus. Pearl millet plants are protogynous, with the stigmas emerging before the anthers. Pearl millet F1 hybrids demonstrate synchronous flowering, so that most of the inflorescences in a crop will be at the protogynous stage with little or no pollen available, which makes F1 hybrids particularly vulnerable to ergot infection. Heavy rain at flowering time washes down pollen, extending the period at which the stigmas are available for infection as well as providing ideal conditions for germination and sporulation of the ergot fungus.
Management
Ergot can be managed in pearl millet, through the use of host plant resistance, pollen management, avoidance and sanitation.

Host plant resistance to ergot can be developed using appropriate inoculation, hybridisation and selection techniques. Sources of host plant resistance are developed and made available by public- and private-sector seed companies.

It has been shown in research station experiments that using pollen donor plants to coincide with the protogynous stage of crop flowering can significantly reduce infection in ergot susceptible pearl millet F1 hybrids.

Avoidance of ergot is achieved through the selection of cultivars that flower during periods of fine dry weather, so that pollen wash and pathogen germination are minimised.

Sanitation measures involve the removal and burning of infected inflorescences as soon ergot symptoms are seen. When this is done at the honeydew stage it will reduce secondary spread within the crop. When done at the sclerotial stage it will reduce the inoculum bank for infections in subsequent seasons and reduce the dangers of consumption of the the poisonous alkaloids getting into food and feed products.

Smut
Tolyposporium penicillariae Bref.

Symptoms
Smut is a disease of pearl millet grain-bearing heads (inflorescences) that can significantly reduce grain yields, wherever the crop is grown.
Infected florets develop as plump sacs or sori, initially green in colour and then turning dark brown or black as the sori mature. The sori are filled with black spores of the causal fungus, hence the name smut.
Cause
Fungus
Comments
Biology and epidemiology: Individual florets are infected by air-borne spores of the causal fungus when the inflorescences are at the protogynous stage. i.e. when the stigmas have emerged before pollination has occurred. Mature spores released from the sori when the crop is threshed are mixed with seed from non-infected florets, and these are the source of infection for the subsequent crop.
Management
Smut is best managed by the use of resistant cultivars.

Downy mildew
Sclerospora graminicola

Symptoms
The earliest symptoms are chlorosis at the base of a leaf, with subsequent leaves on the plant becoming more and more chlorotic, with the chlorosis always extending from the bases towards the tips of the leaves. The underside of chlorotic leaves develop white powdery or downy growth of sporangia and the spores that they bear. There is a distinct margin between diseased leaf tissue at base of leaf and healthy tissue towards tip.
Inflorescences of infected tillers develop the characteristic green-ear symptoms where the grain is replaced by whip-like vegetative structures. Inflorescences can be partially or fully converted to green-ear, depending on the time in inflorescence development at which the infection occurred. Partial green-ear always begins at the base of the inflorescence. Plants infected at an early stage of development, before tillering begins can be killed.
Cause
Oomycete
Comments
Serious disease in Africa and India, occurs wherever millet is grown.
Management
The disease is systemic with the pathogen infecting the growing point of each tiller as the leaf and panicle tissues are being formed.
Primary infection is from oospores which are long-lived in the soil.
Secondary infection is from the spores produced by the sporangia on the undersides of infected leaves. Oospores are formed in necrotic infected plant material, which then contribute to the inoculum bank in the soil.

To reduce infection rogue infected plants when found in the field; treat seeds with an appropriate systemic fungicide prior to planting and continue to spray the crop at least once every 25 days after sowing.

Seed treatment
Pearl millet downy mildew can be effectively controlled through the use of metalaxyl-based fungicide seed treatments. Application rates as low as 2 g a.i. per kg seed, using specially formulated seed-treatment products, can provide complete control of downy mildew even with highly susceptible hybrids. There is no value of subsequent foliar fungicide sprays following effective seed treatment.

On-farm sanitation and selection
In situations where resistant cultivars and seed treatments are not available, farming communities can reduce the incidence of downy mildew in pearl millet by on-farm sanitation practices and the selection of seed from robust downy mildew-free plants.
Secondary spread of downy mildew within a crop is caused by the spores produced on diseased leaves, so removal of diseased plants or tillers at the first sign of disease should minimise secondary spread.
Removal of diseased plants prior to inflorescence emergence, combined with selection of seed for the next season’s sowing from robust, downy mildew-free plants, should also reduce the level of susceptibility in the local cultivar gene pool developing a population of locally DM-resistant cultivars.
Sanitation and selection will be more effective if done on a community basis rather than by individual farmers acting alone. The basis for effective on-farm actions is for farmers to fully understand the cause and epidemiology of the disease.


Host Plant Resistance
Pearl millet downy mildew is best managed by the use of resistant cultivars. Much has been learnt and done in the last 30 years to identify and utilise host plant resistance to this disease, through research done by ICRISAT in collaboration with National Agricultural Research Services (NARS) in India and other countries.
In India, the existence of a strong and effective national agricultural research system together with effective public- and private-sector seed companies, has enabled the development and dissemination of a succession of cultivars and hybrids that have a high degree of resistance to downy mildew.
The pathogen, however, is variable in its pathogenicity, so that cultivars or hybrids resistant to downy mildew in one region may not be resistant elsewhere. The greatest range of pathogenicity occurs in the Sahel zone of Africa, where the host and pathogen have co-evolved over a long period. Pearl millet hybrids developed for resistance to downy mildew in India have been highly susceptible when grown in the Sahel.
Through the ICRISAT-NARS cooperative International Pearl Millet Downy Mildew Nursery program, sources of resistance have been identified that are effective throughout India and right across the African Sahel.

Striga or Purple Witchweed [Orobanchaceae]
Striga hermonthica

Symptoms
Purple Witchweed is the most serious parasitic weed on pearl millet in Africa, causing severe crop losses to this and other crops in the Sahel region. In India Striga asiatica is the most common witchweed species, though here it is not regarded as a serious problem in pearl millet.
Cause
Weed
Comments
Biology & Epidemiology: Seeds of this parasitic plant remain dormant in the soil until exudates from roots of pearl millet plants (and other host species) stimulate their germination. Germ-tubes then invade the pearl millet roots, establishing a pathway for the extraction of moisture and nutrients from the pearl millet plant to enable the witchweed plants to develop and produce a crop of purple flowers. The flowers produce seed which add to the seed bank in the soil for parasitism of future crops.
Management
The most effective management would be achieved by the use of host-plant resistance. In situations where there are no witchweed-resistant cultivars available, farming communities can reduce the levels of damage to the crop by:

a) hand-pulling the witchweed plants as soon as they are visible, thereby reducing the loss of nutrients and moisture by the crop plants and preventing the addition of more witchweed seeds to the seed bank in the soil;
b) the use of “trap” or “decoy” crops such as cowpea or soybean, possibly as an intercrop, which can stimulate germination of the witchweed seeds but are not parasitised, thus reducing the seed bank available for the pearl millet crop.

In addition there are reports of control of witchweed by treating crop seeds with chemicals that prevent the germinating witchweed seeds from parasitising the crop plants. Where such seed treatments have been shown to be effective, are approved for use and are within the economic capabilities of the cultivator, they could be used as part of an integrated management program.

Farming communities can also attempt to develop locally-effective resistant varieties by selection of seed from plants that appear to have not been parasitised.

A combination of effective locally-available management methods is recommended in an integrated management program.