Journal of Heredity 2003:94(4)
© 2003 The American Genetic Association 94:334-340
The Phylogenetic Relationship of Possible Progenitors of the Cultivated Peanut
Address correspondence to A. G. Abbott at the address above.
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The cultivated peanut (Arachis hypogaea L.) is an allotetraploid composed of A and B genomes. The phylogenetic relationship among the cultivated peanut, wild diploid, and tetraploid species in the section Arachis was studied based on sequence comparison of stearoyl-ACP desaturase and oleoyl-PC desaturase. The topology of the trees for both fatty acid desaturases displayed two clusters; one cluster with A genome diploid species and the other with B genome diploid species. The two homeologous genes obtained for each of the two fatty acid desaturases from the tetraploid species A. hypogaea and A. monticola were separated into the A and B genome clusters, respectively. The gene phylogenetic trees showed that A. hypogaea is more closely related to the diploid species A. duranensis and A. ipaensis than to the wild tetraploid species A. monticola, suggesting that A. monticola is not a progenitor of the cultivated peanut. In addition, for the stearoyl-ACP desaturase, the A. duranensis sequence was identical with one of the sequences of A. hypogaea and the A. ipaensis sequence was identical with the other. These results support the hypothesis that A. duranensis and A. ipaensis are the most likely diploid progenitors of the cultivated tetraploid A. hypogaea.
The peanut, or groundnut (Arachis hypogaea L.), is a major commodity crop worldwide, which originated in South America (Simpson et al. 2001). According to the most recent classification, the genus Arachis consists of 69 species and can be divided into nine sections based on morphological characteristics and hybridization data among the species (Krapovickas and Gregory 1994). The section Arachis includes the cultivated peanut and wild species of both annual and perennial forms (Krapovickas and Gregory 1994). All of the wild species identified in the section Arachis are diploid except A. monticola Krapov. and Rigoni, which, like the cultivated peanut, is an allotetraploid. All of the described wild species included in this section can hybridize with A. hypogaea (Krapovickas and Gregory 1994; Smartt and Stalker 1982; Stalker 1990; Stalker and Moss 1987).
Cytological data identified three genomes (A, B, and D) in the section Arachis, with most of the diploid species representing the A genome (Stalker 1991; Stalker et al. 1991). The A genome is characterized by a pair of chromosomes smaller than the other chromosomes; the B genome lacks this smaller chromosome pair. The D genome class consists of a single diploid species, A. glandulifera Stalker. Only a single B genome species, A. batizocoi Krapov. and W. C. Gregory, was initially recognized, but several more have been described (Fernández and Krapovickas 1994). The cultivated peanut A. hypogaea is considered a segmental allotetraploid composed of the A and B genomes (Husted 1933; Strebbins 1957), with probable origin by amphidiploidization of an AB hybrid (Singh 1988; Singh and Moss 1984).
The relationship of the cultivated peanut to its wild relatives and the identification of diploid ancestors have been the emphasis of many studies. A. monticola has been considered to be the most likely candidate for a direct ancestor of the cultivated peanut because this species is also an allotetraploid composed of the A and B genomes, and is located in the same region of South America from which the cultivated peanut is thought to have originated (Simpson et al. 2001). A. monticola successfully hybridizes with A. hypogaea and produces fertile F1 hybrids. However, some investigators considered A. monticola to be a weedy subspecies of A. hypogaea instead of a progenitor (Gregory and Gregory 1976; Kochert et al. 1991; Singh and Moss 1984; Stalker and Moss 1987).
The diploid ancestors of the tetraploid species have not been conclusively determined. Several diploid species in the section have been suggested as ancestors based on various methods of evaluation. Morphological descriptions, phytogeographical evidence, cytogenetic investigation, hybridization data, and molecular analysis have all been utilized to identify possible A and B genome progenitors. Proposed candidates for the A genome have been A. cardenasii Krapov. and W. C. Gregory (Singh and Moss 1982; Smartt et al. 1978), A. duranensis Krapov. and W. C. Gregory (Kochert et al. 1991; Paik-Ro et al. 1992; Singh and Moss 1984), A. correntina (Burkart) Krapov. and W. C. Gregory (Murty and Jahnavi 1986), and A. villosa Benth. (Raina and Mukai 1999; Raina et al. 2001). For some time, A. batizocoi was the only known B genome species and therefore it was usually considered to be one of the progenitors. However, more recent restriction fragment length polymorphism (RFLP) evidence suggests that the B genome donor is not A. batizocoi, but A. ipaensis Krapov. and W. C. Gregory or a closely related form (Kochert et al. 1996). In addition, RFLP analysis of chloroplast DNA determined that A. duranensis was the female parent of the original hybridization event (Kochert et al. 1996). Cytogenetic studies have shown that A. ipaensis is a B genome form, making the cytogenetic and molecular data consistent (Fernández and Krapovickas 1994).
The goal of this study was to utilize DNA sequences of specific gene regions to obtain additional evidence for which diploid species were phylogenetically closest to the individual gene copies in the allotetraploids. This analysis provides additional evidence for identification of the putative progenitor species. We have chosen two of the major fatty acid desaturase genes for this purpose; these encode stearoyl-ACP (acyl carrier protein) desaturase and oleoyl-PC (phosphatidyl choline) desaturase, whose proteins are localized in the chloroplast and endoplasmic reticulum, respectively. Stearoyl-ACP desaturase introduces the first double bond in the fatty acid chain and thereby catalyzes the first step in polyunsaturated oil synthesis. Oleoyl-PC desaturase places the second double bond in the fatty acid chain.
We have isolated and characterized two homeologous gene sequences encoding stearoyl-ACP desaturases (ahFAD1A and ahFAD1B) from the cultivated allotetraploid peanut, A. hypogaea (Tate 1994). The sequence analysis revealed a restriction site polymorphism (RsaI site) between the reading frame sequence of ahFAD1A and ahFAD1B that is also characteristic for gene sequences from A and B genome diploids (Tate 1994). Using this restriction site polymorphism, we showed that both genes are expressed in the developing seeds of A. hypogaea (Jung 2000; Jung et al. 2000b). For the microsomal oleoyl-PC desaturase, two putative homeologous gene sequences (ahFAD2A and ahFAD2B) were isolated and characterized from the cultivated allotetraploid peanut, A. hypogaea (Jung et al. 2000b). As evidenced by the existence of cDNAs for both homeologous genes isolated from a cDNA library of the developing peanut seeds and an reverse transcriptase polymerase chain reaction (RT-PCR)/restriction digestion study, it was determined that both ahFAD2A and ahFAD2B are expressed in A. hypogaea (Jung et al. 2000b). In addition, two different alleles could be identified for ahFAD2A. One of the two ahFAD2A alleles (ahFAD2A-2) gives rise to the functional enzyme and the other (ahFAD2A-1) to a much less active enzyme (Jung et al. 2000a). ahFAD2A-1 was found to have a mutation (D150N) in a residue near a conserved histidine region (HX2HH) that is crucial for enzyme function (Jung et al. 2000a).
In this article we examine the phylogenetic relationship of the cultivated peanut A. hypogaea to its possible progenitors, the wild allotetraploid species A. monticola and diploid species of the genus representing A and B genome species, as well as a D genome species. Maximum parsimony analyses based on the sequences of the two fatty acid desaturase genes were performed to establish the phylogenetic relationship.
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Materials and Methods |
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Genomic DNA Amplification by PCR
DNA was isolated from the leaves of the A. hypogaea ssp. fastigiata var. vulgaris (Table 1) by the CTAB Mini-Prep DNA extraction protocol of Rogers and Bendich (1985). DNA from five diploid wild species (Table 1)—A. batizocoi, A. cardenasii, A. duranensis, A. ipaensis, A. glandulifera—and one wild tetraploid—A. monticola—was isolated by the procedure described in Kochert et al. (1991). Leaves always represented a collection of plants from each accession.
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The PCR was used to amplify a region (877 bp) of stearoyl-ACP desaturase from the above species. The primers were derived from A. hypogaea sequences (GenBank accession no. AF172728). The primer sequences used to amplify this region were as follows: forward primer 5'-GGGCAGTTTGGACAAGGGCA-3' (F3) and reverse primer 5'-ATAGTCCTTGGCAGTG-3' (R7). A region (1133 bp) of oleoyl-PC desaturase was also amplified from the above species using primers derived from A. hypogaea sequences (GenBank accession no. AF272950). The primer sequences were as follows: forward primer 5'-CACTAAGATTGAAGCTC-3' (F0.7) and reverse primer 5'-CTCTGACTATGCATCAG-3' (R1). The amplifications were accomplished in 50 µl reactions with 100 ng of genomic DNA, 0.2 mM each dNTPs, 15 mM MgCl2, 20 pmol of each primer, 2.5 units of Taq DNA polymerase, and the buffer supplied by the manufacturer (Fisher Scientific). PCR temperature cycling was performed as follows: 94°C for 4 min for one cycle; 94°C for 30 sec, 55°C for 1 min, 72°C for 2 min for 35 cycles; 72°C for 4 min using the Perkin-Elmer 480 DNA thermal cycler (Norwalk, CT). The PCR products from A. monticola were cloned into pCR4-TOPO vector (Invitrogen) or pGEM-T Easy (Promega) for the other species following the manufacturer's instructions. The plasmid DNA was isolated using the ABI Prism Miniprep Kit (PE Applied Biosystems), following the manufacturer's protocol. The cloned amplification products were addressed with the gene name and a suffix representing the first letter of the genus and the species to distinguish the sequences according to their origin. Gene names and symbols from the various peanut species used in the phylogenetic analyses are given in Table 2.
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Sequencing of PCR Products
All purified fragments were sequenced using either a Dye Terminator Cycle Sequencing Kit (Perkin-Elmer) or a ThermoSequenase Kit (Amersham Life Sciences). The sequencing reactions were accomplished following the manufacturer's instructions. The sequencing was done using either an Applied Biosystems 373A DNA Sequencer (Applied Biosystems) or a Li-Cor 4200L sequencer (Licor Biosciences) according to the manufacturer's instructions.
PAUP Analysis
Nucleotide sequences were analyzed using GeneWorks version 2.0 (IntelliGenetics). The aligned sequence data were analyzed by the maximum parsimony method using PAUP 4.0 ß2 (Phylogenetic Analysis Using Parsimony; D. Swofford, Smithsonian Institution, Washington, DC). Searches for optimal trees were done by an exact method (branch-and-bound search) without any topological constraints (Swofford 1991). Alignment gaps were treated as an additional character state, as they are derived from insertion/deletion and not from missing data. Bootstrap (1,000 replicates) analyses were performed on data to place confidence estimates on groups contained in the most parsimonious trees generated (Felsenstein 1985). The data are presented as an unrooted cladogram, since there are no sequence data available from a closely related sister group of peanut that could be used as an outgroup. It has been suggested that a radial tree is the better choice if we do not know where the root lies (Hall 2001).
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Results |
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Phylogenetic Relationship Based on Exon and Intron Sequences of Stearoyl-ACP Desaturase
The phylogenetic relationship among the cultivated tetraploid species A. hypogaea, five wild diploid species (A. batizocoi, A. cardenasii, A. duranensis, A. glandulifera, and A. ipaensis) and one wild tetraploid species (A. monticola) was determined by comparing the sequences of the stearoyl-ACP desaturase gene in these species. The 1 kb region of stearoyl-ACP desaturase, which was amplified from the genomic DNA by PCR using primers derived from A. hypogaea sequences, covered two exons and one intron. In A. hypogaea, these primers amplified two sequences (ahFAD1A and ahFAD1B). For each of the diploid species, one sequence was obtained and two different sequences were amplified from the wild tetraploid species (A. monticola), these were designated as amFAD1A and amFAD1B.
To determine whether there are any differences in the rate of evolution between untranslated and translated regions, maximum parsimony analyses were performed separately for the 375 bp sequences from two exons and the 502 bp sequences from the intron. A branch-and-bound search using exon sequences of stearoyl-ACP desaturase yielded one most parsimonious tree (Figure 1A). The topology of the tree based on the exon sequences depicted two major clusters; one includes genes of diploid A genome species A. cardenasii (acFAD1) and A. duranensis (adFAD1), as well as one sequence from the tetraploid species A. hypogaea (ahFAD1A) and A. monticola (amFAD1A), and the other includes genes of diploid B and D genome species as well as the second sequence from the tetraploid species A. hypogaea and A. monticola (Figure 1A). The latter cluster can be subdivided into two groups; one with sequences from A. ipaensis (aiFAD1), A. monticola (amFAD1B), and A. hypogaea (ahFAD1B), the other with sequences from A. batizocoi (abFAD1) and A. glandulifera (agFAD1). Bootstrap values, indicating the percentage a node was supported in 1000 replicates, strongly supported the topology of the tree (Figure 1A). A similar result was obtained from the analysis of a 502 bp sequence from a single intron region of stearoyl-ACP desaturase (Figure 1B). It was notable that the sequences were identical between A. duranensis sequence adFAD1 and A. hypogaea sequence ahFAD1A, and between A. ipaensis sequence aiFAD1 and A. hypogaea sequence ahFAD1B in both of the intron and exon regions examined. For the exon regions analyzed, the A. cardenasii sequence acFAD1 was also the same as the ahFAD1A sequence, but there were significant differences in the intron region. A. monticola sequences amFAD1 and amFAD1B were grouped either with ahFAD1A or ahFAD1B, but were not identical, as in the case of A. duranensis or A. ipaensis.
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Phylogenetic Studies Based on Sequences of Oleoyl-PC Desaturase
Similar analyses were done with gene sequences coding for microsomal oleoyl-PC desaturases. The FAD2 gene sequences of the putative progenitor species (A. batizocoi, A. cardenasii, A. duranensis, A. ipaensis, and A. monticola) as well as A. glandulifera, representing the D genome, could be amplified from the genomic DNA using primers derived from A. hypogaea sequences. These primers amplified three sequences in A. hypogaea (ahFAD2A-1, ahFAD2A-2, and ahFAD2B). For each of the diploid species, one sequence was obtained and three different sequences were amplified from A. monticola. Two of the A. monticola sequences (amFAD2A-1 and amFAD2A-2) were similar to ahFAD2A and the other (amFAD2B) was similar to ahFAD2B, suggesting that amFAD2A-1 and amFAD2A-2 might be alleles of the same gene as in A. hypogaea. Of interest is that amFAD2A-1 and ahFAD2A-1 share the same nucleotide change near a conserved histidine region (HX2HH) that results in the change (D150N) in a residue that is absolutely conserved among other oleoyl-PC desaturases (Table 3). However, apart from this identical mutation site, both A. monticola sequences (amFAD2A-1 and amFAD2A-2) show at least one other sequence difference in comparison to the A. hypogaea sequences (ahFAD2A-1 and ahFAD2A-2), indicating that the observed sequence changes might have occurred independently in both tetraploid species. Both alleles of amFAD2A and ahFAD2A were included in the phylogenetic analysis.
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The parsimony analysis was based on the 1.1 kb sequence from the coding region of oleoyl-PC desaturase amplified from the genomic DNA of the diploid and tetraploid species. A single most parsimonious tree was generated following a branch-and-bound search (Figure 2). The tree topology showed two major groups; one included both alleles of ahFAD2A, both alleles of amFAD2A, and A. duranensis sequence adFAD2, the other included sequences of ahFAD2B, amFAD2B, and A. ipaensis sequence aiFAD2. The sequences from A. cardenasii (acFAD2 ) and A. glandulifera (agFAD2) were clearly separated from these two clusters. A. duranensis sequence adFAD2 shows two sequence differences to the A. hypogaea sequences ahFAD2A-1 and ahFAD2A-2 from which one is common. The sequences for ahFAD2B and amFAD2B are identical, whereas aiFAD2 shows a single nucleotide difference to ahFAD2B and amFAD2B.
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Discussion |
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The polyploid nature of A. hypogaea suggests that the cultivated peanut arose from the genome doubling of an interspecific hybrid within the section Arachis. The identification of this parental hybrid, consisting of an A and B chromosome complement, is unresolved. Kochert et al. (1991, 1996) utilized RFLP and band-sharing methods to demonstrate that one genome of cultivated peanut is most closely related to A. duranensis (A genome) and the other genome to A. ipaensis (B genome). Paik-Ro et al. (1992) also studied RFLP data of several wild diploids and determined that the genetic distance between the cultivated peanut and A. duranensis is the closest among the species investigated.
The tree topologies generated by our sequence data from diploid and tetraploid species of the section Arachis separated A genome-like sequences from B genome-like sequences for both investigated fatty acid desaturases. The bootstrap analysis generated high confidence levels and supports the divergence of different lineages within the section Arachis. The trees clearly separated the two homeologous genes of the fatty acid desaturases from A. hypogaea and A. monticola, and placed one of the genes with A. ipaensis, while the other grouped with A. duranensis. Thus A genome-like species and B genome-like species are represented on our trees and support the allotetraploid nature of the cultivated peanut. Our data also demonstrate that A. batizocoi may not be the B genome donor, but rather a representative of a distinct and unique group, clustering together with the D genome species A. glandulifera. The possibility that A. batizocoi is not an ancestor to the cultivated peanut was first suggested by Smartt et al. (1978) and the hypothesis was based on flower morphology (i.e., flower color) and chromosome characteristics (i.e., satellite size). Molecular data have supported this hypothesis (Kochert et al. 1996; Paik-Ro et al. 1992; Singh et al. 2002). The data from Kochert et al. (1996) indicated that A. batizocoi clusters with A. glandulifera rather than with A. ipaensis (B genome species). This is in agreement with a previous report that the RFLP analysis (Paik-Ro et al. 1992) and molecular data using single-primer DNA amplifications (Halward et al. 1992) clustered A. glandulifera with A. batizocoi, but separately from the A genome species. In our study we included most of the diploid and tetraploid wild species that have been controversially discussed as the most likely putative progenitors of A. hypogaea in the previous literature. However, we did not include A. correntina, suggested by Murty and Jahnavi (1986), and A. villosa.
More recently, Raina and Mukai (1999) proposed A. villosa and A. ipaensis to be the most likely genome donors of the tetraploid species based on in situ hybridization at the rDNA and 5S RNA loci and centromere banding pattern. Random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) data support this hypothesis (Raina et al. 2001). However, previous studies including A. villosa and A. correntina (Kochert et al. 1991, 1996) found little in common among A. villosa, A. correntina, and A. hypogaea.
Our data show that A. hypogaea sequences are highly conserved with A. duranensis and A. ipaensis sequences. In fact, the sequences in both intron and exon regions of stearoyl-ACP desaturase examined in this study are identical. These data, based on sequence comparisons, corroborate previous reports that A. duranensis and A. ipaensis are likely progenitor species for A. hypogaea (Kochert et al. 1991; Paik-Ro et al. 1992; Singh and Moss 1984).
Arachis hypogaea sequences were more closely related to putative diploid progenitor sequences than to wild tetraploid A. monticola sequences. This suggests that A. monticola is not a direct ancestor of A. hypogaea. However, the presence of the two FAD2A alleles, especially the single identical site of a nucleotide difference near the conserved histidine region, could suggest a common ancestor for A. monticola and A. hypogaea. This would be in accordance with previous reports concluding that A. monticola is a weedy derivative of A. hypogaea (Gregory and Gregory 1976; Kochert et al. 1991; Singh and Moss 1984; Stalker and Moss 1987). However, this would require explaining the different mutation rates between A. monticola and A. hypogaea in comparison to the diploid progenitor species. Natural selection of A. monticola versus selection after domestication for A. hypogaea may result in different mutation rates. Domestication can lead to a decrease in genetic diversity. A narrow genetic base characterizes the cultivated peanut, as only very few polymorphisms can be detected in A. hypogaea using different molecular techniques (He and Prakash 1997; Hopkins et al. 1999; Raina et al. 2001; Stalker and Mozingo 2001).
On the other hand, it might be considered a testable hypothesis that the two species, A. monticola and A. hypogaea, may have originated from two separate hybridization events. The larger divergence of A. monticola sequences from the putative diploid species might indicate that the hybridization event leading to A. monticola represents a more ancient event than the one from which A. hypogaea was derived or that different accessions may have been involved. The sequence changes separating the different alleles of FAD2A of both tetraploid species would then have occurred independently. Investigating different accessions of the diploid and tetraploid species may give a clearer picture on this hypothesis. According to Gimenes et al. (2002), A. duranensis showed little polymorphism within accessions but high polymorphism among different accessions. A. cardenasii showed high polymorphism within and between the two accessions analyzed, and A. batizocoi showed low polymorphism within and among the accessions.
Our study shows that sequence comparison can give additional evidence regarding the relationship among species in the genus Arachis. However, more data, especially regarding species variation, are necessary to definitely define the origin of the cultivated peanut.
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Acknowledgments |
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This work was supported entirely by Agratech Seeds Inc.
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Footnotes |
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Department of Genetics and Biochemistry, Clemson University, 100 Jordan Hall, Clemson, SC 29634-0324 (Jung, Tate, Horn, and Abbott); Botany Department, University of Georgia, Athens, GA 30602 (Kochert); and Agratech Seeds Inc., P.O. Box 644, Ashburn, GA 31714 (Moore).
Corresponding Editor: William F. Tracy
Received August 29, 2002
Accepted March 23, 2003
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References |
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Felsenstein J, 1985. Confidence limits on phylogenies: an approach using the bootstrap. Evolution. 39:783-791.[CrossRef][Web of Science]
Fernández A, Krapovickas A, 1994. Cromosomas y evolucion en Arachis (Leguminosae). Bonplandia. 8:187-220.
Gimenes MA, Lopes CR, Galgaro ML, Valls JFM, Kochert GD, 2002. RFLP analysis of genetic variation in species of the section Arachis, genus Arachis (Leguminosae). Euphytica. 123:421-429.[CrossRef]
Gregory WC, Gregory MP, 1976. Groundnut Arachis hypogaea (Leguminosae-Papilionatae). In: Evolution of crop plants (Simmons NW, ed). London: Longman; 151–154.
Hall BG, 2001. Phylogenetic tress made easy: a how-to manual for molecular biologists. Sunderland, MA: Sinauer Associates; 1–179.
Halward TM, Stalker HT, LaRue EA, Kochert GD, 1992. Use of single-primer DNA amplifications in genetic studies of peanut (Arachis hypogaea L.). Plant Mol Biol. 18:315-325.[CrossRef][Web of Science][Medline]
He G, Prakash CS, 1997. Identification of polymorphic DNA markers in cultivated peanut (Arachis hypogaea L.). Euphytica. 97:143-149.
Hopkins MS, Casa AM, Wang T, Mitchell SE, Dean RE, Kochert GD, Kresovich S, 1999. Discovery and characterization of polymorphic simple sequence repeats (SSRs) in peanut. Crop Sci. 39:1243-1247.
Husted L, 1933. Cytological studies of the peanut Arachis. I. Chromosome number and morphology. Cytologia. 5:109-117.
Jung S, 2000. Molecular analysis of high oleate trait and molecular evolution of low-copy genes in allotetraploid peanut [Arachis hypogaea L.] (PhD dissertation no. AAT9976929). Clemson, SC: Clemson University.
Jung S, Powell G, Moore K, Abbott AG, 2000a. The high oleate trait in the cultivated peanut [Arachis hypogaea L.]. II. Molecular basis and genetics of the trait. Mol Gen Genet. 263:806-811.[CrossRef][Web of Science][Medline]
Jung S, Swift D, Sengoku E, Patel M, Teule F, Powell G, Moore K, Abbott AG, 2000b. The high oleate trait in the cultivated peanut [Arachis hypogaea L.]. I. Isolation and characterization of two genes encoding microsomal oleoyl-PC desaturases. Mol Gen Genet. 263:796-805.[CrossRef][Web of Science][Medline]
Kochert GD, Halward TM, Branch WD, Simpson CE, 1991. RFLP variability in peanut cultivars and wild species. Theor Appl Genet. 81:565-570.[Web of Science]
Kochert G, Stalker HT, Gimenes M, Galgaro L, Lopes CR, Moore K, 1996. RFLP and cytogenetic evidence of the origin and evolution of allotetraploid domesticated peanut, Arachis hypogaea (Leguminosae). Am J Bot. 83:1282-1291.[CrossRef][Web of Science]
Krapovickas A, Gregory WC, 1994. Taxonomía del género Arachis (Leguminosae). Bonplandia. 8:1-186.
Murty UR, Jahnavi MR, 1986. The A genome of Arachis hypogaea L. Cytologia. 51:241-250.
Paik-Ro OG, Smith RL, Knauft DA, 1992. Restriction fragment length polymorphism evaluation of six peanut species within the Arachis section. Theor Appl Genet. 84:201-208.
Raina SN, Mukai Y, 1999. Detection of a variable number of 18S-5.8S-26S and 5S ribosomal DNA loci by fluorescent in situ hybridization in diploid and tetraploid Arachis species. Genome. 42:52-59.[CrossRef]
Raina SN, Rani V, Kojima T, Ogihara Y, Singh KP, Devarumath RM, 2001. RAPD and ISSR fingerprints as useful genetic markers for analysis of genetic diversity, varietal identification, and phylogenetic relationships in peanut (Arachis hypogaea) cultivars and wild species. Genome. 44:763-772.[Medline]
Rogers SO, Bendich AJ, 1985. Extraction of DNA from milligram amounts of fresh herbarium and mummified plant tissues. Plant Mol Biol. 5:69-76.
Simpson CE, Krapovickas , Valls JFM, 2001. History of Arachis including evidence of A. hypogaea L. progenitors. Peanut Sci. 28:78-79.
Singh AK, 1988. Putative genome donors of Arachis hypogaea (Fabaceae), evidence from crosses with synthetic amphidiploids. Plant Syst Evol. 160:143-151.[CrossRef]
Singh AK, Moss JP, 1982. Utilization of wild relatives in genetic improvement of Arachis hypogaea L. 2. Chromosome complement of species of section Arachis. Theor Appl Genet. 61:305-314.[Web of Science]
Singh AK, Moss JP, 1984. Utilization of wild relatives in genetic improvement of Arachis hypogaea L. V. Genome analysis in section Arachis and its implication in gene transfer. Theor Appl Genet. 68:355-364.[CrossRef]
Singh KP, Singh A, Raina SN, Singh AK, Ogihara , 2002. Ribosomal DNA repeat unit polymorphism and heritability in (Arachis hypogaea L.) accessions and related wild species. Euphytica. 123:211-220.[CrossRef]
Smartt J, Gregory WC, Gregory MP, 1978. The genomes of Arachis hypogaea. 1. Cytogenetic studies of putative genome donors. Euphytica. 27:665-675.[CrossRef][Web of Science]
Smartt J, Stalker HT, 1982. Speciation and cytogenetics in Arachis. In: Peanut science and technology (Pattee HE and Young CT, eds). Yoakum, TX: American Peanut Research and Education Society; 21–49.
Stalker HT, 1990. A morphological appraisal of wild species in section Arachis of peanuts. Peanut Sci. 17:117-122.
Stalker HT, 1991. A new species in section Arachis of peanuts with a D genome. Am J Bot. 78:630-637.[CrossRef][Web of Science]
Stalker HT, Dhesi JS, Parry DC, Hahn JH, 1991. Cytological and infertility relationships of Arachis section Arachis. Am J Bot. 78:238-246.[CrossRef]
Stalker HT, Moss JP, 1987. Speciation, cytogenetics, and utilization of Arachis species. Adv Agron. 41:1-40.
Stalker HT, Mozingo LG, 2001. Molecular markers of Arachis and marker-assisted selection. Peanut Sci. 28:117-122.
Strebbins GL, 1957. Genetics, evolution, and plant breeding. Indian J Genet Plant Breed. 17:129-141.
Swofford DL, 1991. PAUP: phylogenetic analysis using parsimony, version 3.0s. Champaign, IL: Illinois Natural History Survey.
Tate PL, 1994. A molecular analysis of stearoyl-acyl-carrier-protein desaturase cDNA from Arachis hypogaea L. and its use in a molecular systematic study of the section Arachis nomia nuda (PhD dissertation). Clemson, SC: Clemson University.
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