Pigeon pea

The pigeon pea or toor dal is a perennial legume from the family Fabaceae native to the Eastern Hemisphere. The pigeon pea is widely cultivated in tropical and semitropical regions around the world, being commonly consumed in South Asia, Southeast Asia, Africa, Latin America and the Caribbean.

Etymology and other names

Scientific epithet

The scientific name for the genus Cajanus and the species cajan derive from the Malay word katjang meaning legume in reference to the bean of the plant.

Common English names

In English they are commonly referred to as pigeon pea which originates from the historical utilization of the pulse as pigeon fodder in Barbados. The term Congo pea and Angola pea developed due to the presence of its cultivation in Africa and the association of its utilization with those of African descent. The names no-eye pea and red gram both refer to the characteristics of the seed, with no-eye pea in reference to the lack of a hilum blotch on most varieties, unlike the black-eyed pea, and red gram in reference to the red color of most Indian varieties and gram simply referring to the plant being a legume.

Internationally

Africa

In Benin the pigeon pea is locally known as klouékoun in Fon, otinin in Ede and eklui in Adja. In Cape Verde they are called Fixon Kongu in Cape Verdean creole. In Comoros and Mauritius they are known as embrevade or ambrebdade in Comorian and Morisyen, respectively, in return originating from the Malagasy term for the plant amberivatry. In Ghana they are known as aduwa or adowa in Dagbani. In Kenya and Tanzania they are known as mbaazi in Swahili. In Malawi they are called nandolo in Chichewa. In Nigeria pigeon peas are called fiofio or mgbụmgbụ in Igbo, or in Hausa, and òtílí in Yoruba. In Sudan they are known as, or .

Asia

In India the plant is known by various different names such as

, মিৰি মাহ
, तुवर
, ತೊವರಿ, ತೊಗರಿ ಕಾಳು
or തുവര
, କାକ୍ଷୀ, ତୁବର
, இருப்புலி, காய்ச்சி and துவரை
,
Tibetan:
, توأر
, आढकी

In Persian, it is known as شاخول and is popular in dishes.
In the Philippines they are known as Kadios in Filipino and Kadyos in Tagalog.

The Americas

In Latin America, they are known as guandul or gandul in Spanish, and feijão andu or gandu in Portuguese all of which derive from Kikongo wandu or from Kimbundu oanda; both names referring to the same plant.
In the Anglophone regions of the Caribbean, like Jamaica, they are known as Gungo peas, coming from the more archaic English name for the plant congo pea, given to the plant because of its popularity and relation to Sub-Saharan Africa.
In Francophone regions of the Caribbean they are known as pois d' angole, pwa di bwa in Antillean creole and pwa kongo in Haitian creole.
In Suriname they are known as wandoe or gele pesi, the former of which is derived from the same source as its Spanish and Portuguese counterparts, the latter of which literally translates to 'yellow pea' from Dutch and Sranan Tongo.

Oceania

In Hawaii they are known as or in the Hawaiian language.

History and origin

Origin

The closest relatives to the cultivated pigeon pea are Cajanus cajanifolia, Cajanus scarabaeoides, and Cajanus kerstingii, native to India and the latter West Africa respectively. Much debate exist over the geographical origin of the species, with some groups claiming origin from the Nile river and Western Africa, and the other Indian origin. The two epicenters of genetic diversity exist in both Africa and India, but India is considered to be its primary center of origin with West Africa being considered a second major center of origin.

History

By at least 2800 BCE in peninsular India, where its presumptive closest wild relatives Cajanus cajanifolia occurs in tropical deciduous woodlands, its cultivation has been documented. Archaeological finds of pigeon pea cultivation dating to about 14th century BCE have also been found at the Neolithic site of Sanganakallu in Bellary and its border area Tuljapur, as well as in Gopalpur and other South Indian states.
From India it may have made its way to North-East Africa via Trans-Oceanic Bronze Age trade that allowed cross-cultural exchange of resources and agricultural products. The earliest evidence of pigeon peas in Africa was found in Ancient Egypt with the presence of seeds in Egyptian tombs dating back to around 2200 BCE. From eastern Africa, cultivation spread further west and south through the continent, where by means of the Trans-Atlantic slave trade, it reached the Americas around the 17th century.
Pigeon peas were introduced to Hawaii in 1824 by James Macrae with a few specimens becoming naturalized on the islands, but they wouldn't gain much popularity until later. By the early 20th century Filipinos and Puerto Ricans began to emigrate from the American Philippines and Puerto Rico to Hawaii to work in sugarcane plantations in 1906 and 1901, respectively. Pigeon peas are said to have been popularized on the island by the Puerto Rican community where by the First World War their cultivation began, to expand on the island where they are still cultivated and consumed by locals.

Nutrition

Pigeon peas contain high levels of protein and the important amino acids methionine, lysine, and tryptophan.
The following table indicates completeness of nutritional profile of various amino acids within mature seeds of pigeon pea.

Essential Amino Acid	Available mg/g of Protein	Min. Required mg/g of Protein
Tryptophan	9.76	7
Threonine	32.34	27
Isoleucine	36.17	25
Leucine	71.3	55
Lysine	70.09	51
Methionine+Cystine	22.7	25
Phenylalanine+Tyrosine	110.4	47
Valine	43.1	32
Histidine	35.66	18

Methionine + cystine combination is the only limiting amino acid combination in pigeon pea. In contrast to the mature seeds, the immature seeds are generally lower in all nutritional values, however they contain a significant amount of vitamin C and have a slightly higher fat content. Research has shown that the protein content of the immature seeds is of a higher quality.

Cultivation

Pigeon peas can be of a perennial variety, in which the crop can last three to five years, or an annual variety more suitable for seed production.

Global production

World production of pigeon peas is estimated at 4.49 million tons. About 63% of this production comes from India. The total number of hectares grown to pigeon pea is estimated at 5.4 million. India accounts for 72% of the area grown to pigeon pea or 3.9 million hectares. Africa is the secondary centre of diversity and at present it contributes about 21% of global production with 1.05 million tons. Malawi, Tanzania, Kenya, Mozambique and Uganda are the major producers in Africa. Malawi's Nandolo Farmers' Association is supported by international aid via the charity Christian Aid.
The pigeon pea is an important legume crop of rainfed agriculture in the semiarid tropics. The Indian subcontinent, Africa and Central America, in that order, are the world's three main pigeon pea-producing regions. Pigeon peas are cultivated in more than 25 tropical and subtropical countries, either as a sole crop or intermixed with cereals, such as sorghum, pearl millet, or maize, or with other legumes, such as peanuts. Being a legume capable of symbiosis with Rhizobia, the bacteria associated with the pigeon pea enrich soils through symbiotic nitrogen fixation.
The crop is cultivated on marginal land by resource-poor farmers, who commonly grow traditional medium- and long-duration landraces. Short-duration pigeon peas suitable for multiple cropping have recently been developed. Traditionally, the use of such input as fertilizers, weeding, irrigation, and pesticides is minimal, so present yield levels are low. Greater attention is now being given to managing the crop because it is in high demand at remunerative prices.
Pigeon peas are very drought-resistant and can be grown in areas with less than 650 mm annual rainfall. With the maize crop failing three out of five years in drought-prone areas of Kenya, a consortium led by the International Crops Research Institute for the Semi-Arid Tropics aimed to promote the pigeon pea as a drought-resistant, nutritious alternative crop.

Nitrogen fixation

Legumes, which provide highly nutritious products and contribute to soil fertility through biological nitrogen fixation, are one of the most important crops in mixed crop-livestock systems. Cajanus cajan is an important legume crop with a high N-fixation ability. Plant-growth promoting rhizobacteria, together with strains of Rhizobium, can enhance growth and nitrogen fixation in pigeon pea by colonizing thenselves in the plant nodules. These bioinoculants can be added as a single species but also as combined communities. Using a single bioinoculant shows benefits, but mixed communitites of different bioinoculatns have a greater positive impact on nodulation, plant dry mass, as well as shoot and root length. These different community species have different functions for the pigeon pea:

Bioinoculant	Function
Azotobacter chroococcum	promotes plant growth as a biofertilizer
Bacillus megaterium	produces nematode-targeting antibiotics and potentially influencing cytokinin signaling and supports the nitrogen yield of the plant especially during flowering and maturity stages
Pseudomonas fluorescens	produces bioactive metabolites and siderophores that combat plant pathogens and supports the denitrification process
Trichoderma harzianum	promotes soil health by production of enzymes and secondary metabolites that enhibit harmful soilborne pathogens and nutrient cycling by promoting root development