An overview of peanut and its wild relatives

Abstract

The legume Arachis hypogaea, commonly known as peanut or groundnut, is a very important food crop throughout the tropics and sub-tropics. The genus is endemic to South America being mostly associated with the savannah-like Cerrado. All species in the genus are unusual among legumes in that they produce their fruit below the ground. This profoundly influences their biology and natural distributions. The species occur in diverse habitats including grasslands, open patches of forest and even in temporarily flooded areas. Based on a number of criteria, including morphology and sexual compatibilities, the 80 described species are arranged in nine infrageneric taxonomic sections. While most wild species are diploid, cultivated peanut is a tetraploid. It is of recent origin and has an AABB-type genome. The most probable ancestral species are Arachis duranensis and Arachis ipaënsis, which contributed the A and B genome components, respectively. Although cultivated peanut is tetraploid, genetically it behaves as a diploid, the A and B chromosomes only rarely pairing during meiosis. Although morphologically variable, cultivated peanut has a very narrow genetic base. For some traits, such as disease and pest resistance, this has been a fundamental limitation to crop improvement using only cultivated germplasm. Transfer of some wild resistance genes to cultivated peanut has been achieved, for instance, the gene for resistance to root-knot nematode. However, a wider use of wild species in breeding has been hampered by ploidy and sexual incompatibility barriers, by linkage drag, and historically, by a lack of the tools needed to conveniently confirm hybrid identities and track introgressed chromosomal segments. In recent years, improved knowledge of species relationships has been gained by more detailed cytogenetic studies and molecular phylogenies. This knowledge, together with new tools for genetic and genomic analysis, will help in the more efficient use of peanut's genetic resources in crop improvement.

The genome sequences of Arachis duranensis and Arachis ipaensis, the diploid ancestors of cultivated peanut

“…Rarely, water-driven soil erosion will disperse seeds downhill. This pattern of dispersal, coupled with a high rate of self-pollination, has led to species distributions that consist of patchy, often highly homozygous populations distributed over areas defined by major river systems 47 .…”

Impact of Molecular Genetic Research on Peanut Cultivar Development

“…Introgression of traits using conventional breeding is a long and arduous task due to the cross incompatibilities and ploidy barriers between diploid wild and tetraploid cultivated along with poor agronomic performance of interspecific material. Two pathways for introgression have been tested in peanut, one involving a triploid intermediate from hybridization of cultivated tetraploid with wild diploid and the other a synthetic tetraploid hybrid crossed with cultivated tetraploid [48,92]. The latter is the most direct route for introgressing useful genes into A. hypogaea.…”

Yield, market quality, and leaf spots partial resistance of interspecific peanut progenies

“…Research progress over the last few years has provided a better comprehension about the origin of cultivated peanut and its putative relatives, including the development of amphidiploids combining species of different genomes, cross-compatible to A. hypogaea (Fávero et al 2006, Fávero et al 2009, Bertioli et al 2011). Resistance to peanut leaf spots have been identified in a large number of accessions with A and B genomes, including the wild specie A. duranensis (Fávero et al 2009).…”