Groundnut, L'arachide
(Arachis hypogaea Linnaeus)

Groundnut, an important cash crop, is an annual legume. Its seeds are a rich source of edible oil (43-55%) and protein (25-28%). About two thirds of world production is crushed for oil and the remaining one third is consumed as food. Its cake is used as feed or for making other food products and haulms provide quality fodder.

Morphology

Botanically cultivated groundnut can be classified into two subspecies which mainly differ in their branching pattern: subspecies hypogaea with alternate branching and subspecies fastigiata with sequential branching. Each subspecies is again divided into two botanical varieties; subsp. hypogaea into var. hypogaea (virginia) and var. hirsuta; and subsp. fastigiata into var. fastigiata (valencia), var. vulgaris (spanish), var. peruviana, and var. aequatoriana. In trade, the bold-seeded types are referred to as Virginia, the small seeded as Spanish, and a third type Runner is also recognized. The flowers are born in the axils of the leaves mostly near the base of plant and have generally yellow petals. It is a self pollinated crop. After fertilization stalk of ovary elongates and forms peg which contains fertilized ovules at the tip. The growth of peg is positively geotropic until it penetrates soil to some depth (7 cm). The tip then becomes diageotropic and ovary starts developing into a fruit called pod which contains seeds. Generally it takes about 60 days from fertilization to full pod maturity.

Sufficient variability exists in groundnut for various morphological and economic traits: seed size, (17-124 g 100-seeds-1), seed color (white, light rose, rose, red, purple, white blotched with purple red), number of seeds pod-1 (1-5), and pod length (11-83 mm) and pod breadth (9-27 mm).

Distribution

Groundnut originated in the southern Bolivia/north west Argentina region in south America and is presently cultivated in 108 countries of the world. Asia with 63.4% area produces 71.7% of world groundnut production followed by Africa with 31.3% area and 18.6% production, and North-Central America with 3.7% area and 7.5% production. Important groundnut producing countries are China, India, Indonesia, Myanmar, Thailand, and Vietnam in Asia; Nigeria, Senegal, Sudan, Zaire, Chad, Uganda, Cote d'Ivory, Mali, Burkina Faso, Guinea, Mozambique, and Cameroon in Africa; Argentina and Brazil in South America and USA and Mexico in North America.

Adaptation

The ideal growing conditions for groundnut are well-drained, light colored, loose friable, sandy loam soil, availability of optimum moisture in pod zone, and an optimum mean daily temperature of about 30 0C. It can be grown either as a sole crop or in combination with other crops in inter or mixed cropping. Early leaf spot, late leaf spot, rust, and Sclerotium rolfsi among fungal diseases; bud necrosis virus, tomato spotted wilt virus, peanut stripe virus, and rosette among virus diseases; and jassids, thrips, termites, leaf miner, Spodoptera, and white grub among insect pests, and aflatoxin contamination are important biotic factors. Among abiotic stresses drought, low pH, and low temperatures are important. These occur in various combinations in Asia, Africa, and Americas.

Crop improvement

Development of high-yielding cultivars of desired duration having resistance/tolerance to single or multiple stresses and developing stress management strategies are the main objectives of groundnut improvement programs in the world including the one at ICRISAT. At ICRISAT, these objectives have been adequately supported by Genetic Resources Program which maintains 13, 460 groundnut accessions including 197 of wild Arachis species from 89 countries. The wild Arachis species are reservoir of genes for high levels of resistance to various stresses. Our efforts have yielded management strategies including genetic resistance for rust, late and early leaf spots, aflatoxin, rosette, and peanut bud necrosis virus. We have developed short- and medium-duration and confectionery varieties with multiple tolerance/resistance. More than 50 germplasm/breeding lines which originated from ICRISAT have either been released as cultivars or are in on-farm trials in 25 countries of Asia and Africa. Now these cultivars are beginning to be used in the production systems, specially those characterized by low inputs and resources poor farmers. Fifteen other improved germplasm are used in the national breeding programs. These would result in capacity building of National programs in developing technologies for sustainable groundnut production.

Novel techniques such as genetic transformation, molecular markers added selection, and gene transfer from alien sources are yet to make an impact on groundnut research.