RA 00183.pdf - OAR@ICRISAT

Germplasm of Wild Species of Arachis:
Evaluation and Utilization 1
C.E. Simpson 2
The genus Arachis L originated somewhere on the ancient Brazilian shield well before the
occurrence of a series of mid-Tertiary uplifts of the shield. After the uplifts, the genus, along
with the peneplane, was distributed by downward moving soil and water in the various river
valleys of north-central, eastern, and southern Brazil; the eastern half of Bolivia, east of the
present Andes ranges; almost all of Paraguay; north-west, north, and eastern Argentina; and
west and north Uruguay. As the South American continent continued its westward drift, the
Andes continued to be graded upward and eventually lifted the most recently evolved species
to elevations several hundred meters higher than their progenitors. This gives a false
impression of evolutionary sequence if you think of newer species evolving "downstream"
without considering the uplifting action at work on the Cordillera.
The genus Arachis, represented by some 70 to 80 species, has been an opportunistic
taxon, taking advantage of many diverse habitats; from the Catinga of Northeast Brazil, to the
forests of the Amazon, to the swamps of the Gran Pantanal, to the thorn-thickets of the Gran
Chaco in Bolivia, Paraguay and Argentina.
The genus can be divided into eight rather distinct taxonomic sections (Table 1).
T a b l e 1. S e c t i o n s a n d t h e n u m b e r of s p e c i e s in Arachis.
Section
Arachis
Erectoides
Extranervosae
Ambinervosae
Triseminalae
Caulorhizae
Procumbensae
Rhizomatosae
Ploidy level
2 x & 4 x
2x
2x
2x
2x
2x
2x
2 x & 4 x
No. of species.
34
17
8
4
1
3
10
3
These sections are genetically well isolated, with very few intersectional crosses being
successful. The Arachis section is most important to groundnut breeders because it contains
1. Collaborating Principal Investigator on the Texas A&M University Peanut CRSP "Breeding Peanuts for Semi-Arid
Environments", Dr O. D. Smith. Supported in part by USAID Grant No. DAN-4048-G-00-0041-00.
2. Professor/Peanut Breeder, Texas Agricultural Experiment Station, P.O. Box 292, Stephenville, Texas, 76401,
USA.
Citation: ICRISAT (International Crops Research Institute for the Semi-Arid Tropics). 1991. Summary Proceedings of
the Second ICRISAT Regional Groundnut Meeting for West Africa, 11-14 Sep 1990, ICRISAT Sahelian Center,
Niamey, Niger. Patancheru, A.P. 502 324, India: ICRISAT.
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