The guar or cluster bean, with the botanical name Cyamopsis tetragonoloba, is an annual legume and the source of guar gum. It is also known as gavar, gawar, or guvar bean.
The origin of Cyamopsis tetragonoloba is unknown, since it has never been found in the wild. It is assumed to have developed from the African species Cyamopsis senegalensis. It was further domesticated in South Asia, where it has been cultivated for centuries. Guar grows well in semiarid areas, but frequent rainfall is necessary.
This legume is a valuable plant in a crop rotation cycle, as it lives in symbiosis with nitrogen-fixing bacteria. Agriculturists in semi-arid regions of Rajasthan follow crop-rotation and use guar to replenish the soil with essential fertilizers and nitrogen fixation, before the next crop. Guar has many functions for human and animal nutrition, but the gelling agent in its seeds (guar gum) is the most important use. Demand is rising due to the use of guar gum in hydraulic fracturing (oil shale gas).. It is also a major ingredient of the toy Slime. About 80% of world production occurs in India, but due to strong demand, the plant is being introduced elsewhere.
Biology
Cyamopsis tetragonoloba grows upright, reaching a maximum height of up to . It has a main single stem with either basal branching or fine branching along the stem. Guar taproots can access soil moisture in low soil depths. This legume develops root nodules with nitrogen-fixing soil bacteria rhizobia in the surface part of its rooting system. Its leaves and stems are mostly hairy, depending on the cultivar. Its fine leaves have an elongated oval shape () and of alternate position. Clusters of flowers grow in the plant axil and are white to blueish in color. The developing pods are rather flat and slim containing 5 to 12 small oval seeds of length (TGW = ). Usually mature seeds are white or gray, but with excess moisture they can turn black and lose germination capacity. The chromosome number of guar seeds is 2n=14. The seeds of guar beans have a remarkable characteristic. Its kernel consists of a protein-rich germ (43–46%) and a relatively large endosperm (34–40%), containing large amounts of the galactomannan. This is a polysaccharide containing polymers of mannose and galactose in a ratio of 2:1 with many branches. Thus, it exhibits a great hydrogen bonding activity having a viscosifying effect in liquids.
Cultivation
Climate requirements
Guar is drought-tolerant and sun-loving, but it is susceptible to frost. Although it can cope with little but regular rainfall, it requires sufficient soil moisture before planting and during maturation of seeds. Frequent drought periods can lead to delayed maturation. On the contrary, excessive moisture during the early growth phase and after maturation lead to lower seed quality. Guar is produced near to coastal areas in the Gandhidham region of Kutch, Gujarat, India.
Soil requirements
Cyamopsis tetragonoloba (L.) can grow on a wide range of soil types. Preferably in fertile, medium-textured and sandy loam soils that are well-drained, since waterlogging decreases plant performance. Guar grows best in moderate alkaline conditions (pH 7–8) and is tolerant of salinity. Its taproots are inoculated with rhizobia nodules and thus it produces nitrogen-rich biomass and improves soil quality.
Cultural practices
Cultivation areas
Guar is grown principally in north-western India with smaller crops grown in the semiarid areas of the high plains of Texas in the US, Australia and Africa. The most important growing area centres on Jodhpur in Rajasthan, India, where demand for guar for fractionation produced an agricultural boom as in 2012. Currently [When? As of 2023?], India is the main producer of cluster bean, accounting for 80% production of the world's total, while the Rajasthan, Gujarat and Kutch regions occupy the largest areas (82.1% of total) dedicated to guar cultivation. In addition to its cultivation in India, the crop is also grown as a cash crop in other parts of the world. Several commercial growers have converted their crops to guar production to support the increasing demand for guar and other organic crops in the United States.