Global Resources of Genetic Diversity in Peanut

Peanut or groundnut (. Arachis hypogaea L.) is an annual herb, with geocarpic fruits, and an indeterminate growth habit. It is classified as a legume in the plant family Fabaceae. Carl Linneaus first described the cultivated species in 1753, as A. hypogaea L. Cultivated peanut can be classified into two subspecies, fastigiata and hypogaea, based on the presence or absence of floral axes on the main stem. They can be further divided into six botanical varieties (subspecies hypogaea: var. hirsuta, and var. hypogaea; subspecies fastigiata: var. aequatoriana, var. fastigiata, var. peruviana, and var. vulgaris) based on a range of morphological characteristics. The cultivated peanut is a self-pollinating allotetraploid (AABB genome, 2. n=. 4. x=. 40) putatively derived from the natural hybridization of two wild diploid species Arachis duranensis (AA genome, 2. n=. 2. x=. 20) and Arachis ipaënsis (BB genome, 2. n=. 2. x=. 20). It is well documented that cultivated peanut has a narrow genetic base which was likely due to a single polyploidization event that isolated it from the wild species and created small founder populations and a significant genetic bottleneck in the cultigen. Genetic variability is known to decline in proportion to the severity of the bottleneck and the smaller the population and the longer it remains small the more the allelic diversity erodes with the low frequency alleles being most at risk during a bottleneck. Nucleotide substitution rates suggest that the A, B, and K (. Arachis batizocoi) genomes diverged fairly recently, between 2.3 and 2.9. million. years ago. Large germplasm collections are maintained in India, China, and the United States.