Chickpea Taxonomy and Biosystematics
Origin and domestication
Chickpea (Cicer arietinum L.) is one of the pulse crops domesticated in the Old World ca 7000 years ago. Most probably, it has originated in an area of south-eastern Turkey and Syria. Three wild annual Cicer species, C. bijugum, C. echinospermum, and C. reticulatum, closely related to chickpea, cohabit with the cultivar in this area. Chickpea is not known to occur in the wild and some of the earlier reports on its mistaken wild status could be due to volunteers or escapes from cultivation. Chickpea is cultivated from the Mediterranean basin to the Indian sub-continent and southward to Ethiopia and the East African Highlands. It has been introduced to the Americas and gained popularity especially in Mexico. However, the crop assumed greatest significance in Indian subcontinent. A good knowledge of the various Cicer species is essential to enable the scientific community to make efficient use of the genetic resources in chickpea improvement.
The Cicer species occur from sea level (e.g. C. arietinum, C. montbretii) to over 5000 m (C. microphyllum) near glaciers in the Himalayas. The cultivated species, C. arietinum is found only in cultivation and can not colonise successfully without human intervention. The wild species (e.g. C. reticulatum, C. bijugum) occur in weedy habitats (fallow or disturbed habitats, roadsides, cultivated fields of wheat, and other places not touched by man or cattle), mountain slopes among rubble (e.g. C. pungens, C. yamashitae), and on forest soils, in broad-leaf or pine forests (e.g. C. montbretii, C. floribundum).
Chickpea is the only domesticated species under the genus Cicer, which was originally classified in the tribe vicieae of the family Leguminosae and sub family, papilionoideae. Based on the pollen morphology and vascular anatomy, Cicer is now set aside from the members of Vicieae and is classified in its own monogeneric tribe, Cicereae Alef. The tribe, Cicereae comes closer to the tribe, Trifolieae, which differs from the former in having hypogeal germination, tendrils, stipules free from the petiole, and nonpapillate unicellular hairs.
The genus Cicer comprises 43 species and is divided into two subgenera. The subgenus, Pseudononis is characterized by small flowers (normally 5-10 mm), subregular calyx, with hardly gibbous base, with sublinear nearly equal teeth. It comprises two sections, Monocicer (annuals, with firm erect or horizontal stems branched from the base or at middle) and section, Chamaecicer (annuals or perennials, with thin creeping branched stem, and small flowers). The section, Monocicer comprising all annual species most important to breeders, is subdivided into three series, Arietina (characterized by imparipinnate leaves, with none to small arista), cirrhifera (leaves ending in a tendril, with short arista), and Macro-aristae (leaves imparipinnate, long arista). Likewise, section Chamaecicer is divided into two series, Annua and Perennia. The subgenus, Viciastrum (perennials, characterized by medium large flowers, calyx strongly gibbous at the base, with unequal teeth) comprises two sections, Polycicer and Acanthocicer. Polycicer (leaf rachis ending in a tendril or a leaflet, never a spine) is divided in to two sub-sections, Nano-polycicer (with creeping rhizome, short stem, imparipinnate leaves, weak and short arista) and Macro-polycicer (with short rhizome, non-creeping, stems ascending to 75 cm, firm arista longer than pedicel). Macro-polycicer is further divided into six series: persica (inflorescences 1-2 flowered, flowers 14 -15 mm, calyx teeth 2-4 times the tube, stipules 14-15 mm, half as large as the leaflets, which are in 2-12 pairs); Anatolo-Persica (inflorescences 1-2 flowered, flowers 20-27 mm, calyx teeth short, stipules smaller than the largest leaflets, which are in 4 -9 pairs); Europaeo-Anatolica ( inflorescences 2-5 flowered, bracts foliolate, stipules small or up to half as large as the leaflets, which are in 4-8 pairs); Flexuosa (inflorescences 1-2 flowered, bracts minute, stipules much smaller than the leaflets, which are in 4 -13 pairs); Songarica (inflorescences 1-2 flowered, bracts minute, stipules more or less equal to the largest leaflets, which are in 2-18 pairs); and Microphylla (inflorescences 1-2 flowered, bracts minute, stipules smaller than or equal to the largest leaflets, which are in 7- 10 pairs). Section Acanthocicer (perennials, with branched stems with woody base, persistent spiny leaf rachis, spiny calyx teeth, and large flowers) is divided into 3 series: Pungentia (Foliate or small spiny stipules), Macrocantha (long spiny stipules), and Tragacanthoidea (small triangular incised stipules). The species under various sections and series with their salient features are presented in Table 1.Cytotaxonomy and interspecific hybridization
Chromosome number in Cicer species can be generalized as 2n=2x= 16, although varying numbers both for chickpea (2n= 2x= 14, 16, 24, 32, 33) and other wild Cicer species (2n=14, 16, 24) have been reported, but could not be confirmed by other workers. Studies on biosystematic relations between chickpea and its wild relatives following interspecific hybridization have been limited to the 9 annual species, C. arietinum (chickpea), C. reticulatum, C. echinispermum, C. judaicum, C.pinnatifidum, C. bijugum, C. cuneatum, C. chorassanicum, and C. yamashitae. Based on the crossability and morphological similarities, the 9 annual species have been classified into 4 groups: the above first 3 species as group 1, the next 3 species along with C. yamashitae as group 2, and the remaining 2 species as two separate groups. Of these, only two species, C. reticulatum and C. echinospermum produced viable hybrids with chickpea. Gene exchange, is normal between chickpea and C. reticulatum, while it is restricted due to high sterility in the hybrids involving C. echinospermum. In general morphology, physiology, and genetics, C. reticulatum comes closest to the cultigen, making it a possible progenitor of chickpea. However, considering the polymorphic nature of ancestral populations and complex nature of domestication, one can not rule out the other possibilities, such as C. reticulatum and the cultigen sharing a common ancestor or a polyphyletic origin of chickpea.
Based on the electrophoretic study of water- soluble seed protein patterns, a close affinity between chickpea and C. reticulatum has been found and a monophyletic origin has been suggested for chickpea by some authors. From recent studies on assessment of allelic variation for 23 isozyme loci in 36 accessions representing 8 wild species and 25 accessions of the cultivar, following four genetic groups were recognized: Group one (C reticulatum, C.arietinum, and C. echinospermum) , group two (C. bijugum, C. pinnatifidum), group three (C. judaicum, C. yamashitae, C. chorassanicum, C. anatolicum, and C. songaricum; the latter two are perennials) and group four (C. cuneatum). These groupings showed good agreement with those based on morphological studies, and partial agreement with those obtained from crossability and cytogenetic studies.
Two major cultivar types designated as `desi' (= microsperma) and `kabuli' (= macrosperma) have emerged under domestication. In addition `gulabi', pea shaped forms of local importance are also recognized. Desi chickpeas are small and angular with rough brown to yellow testas, while kabuli types are relatively large, plump, and with smooth cream colored testas. Kabuli types are considered relatively more advanced because of their larger seed size and reduced pigmentation achieved through conscious selection. Study at ICRISAT revealed that desi and kabuli types differ in their dietary fiber components of seed both qualitatively and quantitatively. Kabuli types contain higher amount of dietary fiber, particularly cellulose and hemicellulose.