Reticulate evolution and seed crops peanut

Raina and Mukai (1999) list the peanut, Arachis hypogaea, as the third most important grain legume crop in the world. One indication of its utility as a food source for H. sapiens populations is reflected by the fact that Americans consume nearly 1.1 billion kg of peanuts per year (Barkley et al. 2007). Raina and Mukai (1999) supported their contention by citing A. hypogaea's cultivation across divergent agricultural practices in Asia, Africa, and North, Central and South America (the latter being its place of origin; reviewed by Kochert et al. 1996 and Jung et al. 2003), reflective of its adaptation to a diverse array of tropical and subtropical environments.

A. hypogaea's fundamental importance for humans resides not only in its use as a direct source of food, but also because it functions as (1) a feedstock for domesticated animals, (2) a source of high-quality oil, and (3) a ground cover species (Raina and Mukai 1999). This species is also of economic significance for producer countries. For example, the United States is the third largest exporter of peanuts after China and Argentina (Dohlman and Livezey 2005). Peanuts represent a relatively small share of total agricultural production in the United States, yet in 2004, income from this crop was nearly US$800 million (Dohlman and Livezey 2005). Its importance can be seen particularly at the state level. (A. hypo-gaea cultivation takes place largely in the states of Georgia, Alabama, Florida, South Carolina,

Texas, Oklahoma, New Mexico, Virginia, and North Carolina.) Thus, although less than 1% of US crop income derives from A. hypogaea it produced the second highest amount of crop revenue in Georgia and was also a leading income producer for Alabama and Florida (Dohlman and Livezey 2005).

Section Arachis, of the genus Arachis—in which cultivated peanut belongs—contains 31 species (Fávero et al. 2006). Of these 31 species, 29 are diploid taxa and 2 are allopolyploid derivatives; the 2 allotetraploids are Arachis montícola and A. hypogaea. A variety of analyses have been performed to infer the diploid parents for A. monticola and A. hypogaea, but with most research directed at understanding the derivation of the cultivar (Kochert et al. 1996; Raina and Mukai 1999; Jung et al. 2003; Fávero et al. 2006). For example, Kochert et al. (1996) utilized chromosome markers along with patterns of genetic variation at both nuclear and chloroplast loci to decipher evolutionary relationships among the diploid and tetraploid species. These data led to the conclusion that the cultivated lineage is derived from hybridization between the diploid species Arachis duranensis and Arachis ipaensis (Kochert et al. 1996). Results from this analysis also suggested that the most likely geographic point of origin was northern Argentina or southern Bolivia (Kochert et al. 1996). Finally, the maternally inherited cpDNA was donated by plants from A. duranensis, indicating this lineage's role as the female parent in the original cross with A. ipaensis (Kochert et al. 1996). Subsequent studies that examined additional genetic loci and progeny from artificial crosses had, in the main, validated Kochert et al.'s (1996) conclusions concerning the progenitor genomes found in cultivated peanut. In contrast, it has recently been inferred that the allotetraploid A. monticola lineage was the direct progenitor of allotetraploid A. hypogaea (Seijo et al. 2007). Regardless of whether or not the cultivar was formed independently from crosses between diploid taxa, or arose directly from another allo-polyploid species, the New World derivation of the plant that provides the highly nutritious peanut oil, butter, and seeds (Barkley et al. 2007) provides yet another example of processes that underlie the web of life.

Was this article helpful?

0 0

Post a comment