Species Of Section Arachis Research Articles

Variation in chromosomal DNA associated with the evolution of Arachis species

The 2C nuclear DNA amounts were determined for 99 accessions, representing 23 Arachis species from 8 of 9 taxonomic sections, and two synthetic amphidiploids. Mean 2C DNA amounts varied by 15.20%, ranging from 10.26 to 11.82 pg, between accessions of Arachis hypogaea (2n = 4x = 40). Nuclear DNA content variation (5.33-5.91 pg) was also detected among Arachis duranensis (2n = 2x = 20) accessions. The intraspecific variation in the two species may have resulted from indirect selection for favourable genome sizes in particular environmental conditions. The accessions belonging to A. hypogaea ssp. hypogaea (mean value 11.27 pg) with longer life cycle had significantly larger mean DNA content than the accessions of A. hypogaea ssp. fastigiata (mean value 10.97 pg). For 20 diploid (2n = 2x = 20) species of the genus, 2C nuclear DNA amounts ranged from approximately 3 to 7 pg. The diploid perennial species of section Arachis have about 12% more DNA than the annual species. Comparisons of DNA amounts show that evolutionary rating is not a reliable guide to DNA amounts in generic sections of the genus; lower DNA values with evolutionary advancement were found in sections Heteranthae and Triseminatae, but the same was not true for sections Arachis and Caulorrhizae. Similarly, there is evidence of significant differences in DNA content between 4 ancient sections (Procumbentes, Erectoides, Rhizomatosae, and Extranervosae) of the genus. The occurrence of genome size plasticity in both A. duranensis and A. hypogaea provides evidence that A. duranensis could be one of the diploid progenitors of A. hypogaea. The DNA content in the two synthetic amphidiploids corresponded to the sum value estimated for parental species. Key words : Arachis species, genome size, Arachis hypogaea, Arachis duranensis, intraspecific variation.

Early Reproductive Ontogeny in Interspecific Crosses of Arachis hypogaea and Section Arachis Species

Wild Arachis species have been recognized as sources of resistance to pests and pathogens that infect A. hypogaea L. and cause substantial yield losses. However, utilization of these genetic resources for crop improvement has been difficult. This study was conducted to ( a) understand the processes of early embryo growth and development in four Arachis species, two A. hypogaea cultivars and their hybrids and ( b) identify parental compatibilities in reciprocal crosses of A. hypogaea. The results indicated that delayed fertilization beyond 24 h, coupled with slow proembryo growth, leads to embryo abortion in many interspecific crosses. For example, in female A. cardenasii crosses, lack of or delayed fertilization leads to failure to obtain hybrids. When A. batizocoi was used as a female parent, delayed fertilization and the inability of quiescent proembryos to resume growth after soil penetration caused abortion. Embryos of A. hypogaea × A. glandulifera crosses developed normally during the first 21 d after fertilization, but then aborted at a later time. In this study, A. hypogaea was always a better female parent than the wild Arachis species. Increasing the number of pollinations per cross, using the cultivated species as the female parent, utilizing different A. hypogaea varieties, and embryo rescue techniques are suggested to improve the probability of obtaining interspecific hybrids in Arachis.

Seed storage protein variation in Arachis species

Seventy-two accessions, representing 22 species from sections Arachis, Erectoides, Extranervosae, and Triseminalae of the genus Arachis, were screened for seed storage protein polymorphism. Variation was detected between sections, between genome types, between species, and in some cases between different accessions of the same species or different seeds of the same accession. Arachis duranensis and one accession of A. cardenasii were found to have identical protein patterns. The greatest dissimilarity was found between species of the section Extranervosae and species of the section Triseminalae. Those of section Erectoides showed much similarity with some species of section Arachis. Protein polymorphism was shown to distinguish the two subspecies of A. hypogaea (fastigiata and hypogaea) in 27 of 28 cases. The seed protein profile of A. monticola was a combination of seed protein profiles from the two A. hypogaea subspecies. The relatedness between the various species was calculated and those that had the greatest similarity with A. hypogaea were A. spegazzinii and A. batizocoi.

Genetic variation detectable with molecular markers among unadapted germ-plasm resources of cultivated peanut and related wild species

Peanut germ plasm consists of the cultivated allotetraploid species Arachis hypogaea L. and a large number of wild species, which are nearly all diploids. Our previous work indicated a very low level of genetic variability in American cultivars, as assayed by restriction fragment length polymorphism (RFLP) analysis. Since American cultivars might represent a narrow genetic base, we expanded our study to include unadapted germ-plasm lines from the various South American centers of origin, Africa, and China, where considerable morphological and physiological variability has been reported to exist. Wild species of section Arachis were included in the evaluations since they show a high degree of variation when assayed by RFLPs. Three methods were used to assay for RFLP variation: (i) conventional RFLP analysis using random genomic clones from peanut and cDNA clones from peanut and alfalfa (Medicago sativa); (ii) polymerase chain reaction (PCR) amplification of random primer sequences; (iii) four-cutter analysis of PCR-amplified fragments. In all cases a very low level of variability was found in cultivated peanut, while abundant variability was present among wild diploid species. The results are discussed in terms of peanut evolution and significance to peanut breeding.Key words: polymerase chain reaction, Arachis hypogaea, restriction fragment length polymorphism.

A NEW SPECIES IN SECTION ARACHIS OF PEANUTS WITH A D GENOME

Arachis glandulifera Stalker is a diploid (2n = 2x = 20) taxon in section Arachis native to eastern Bolivia. Plants of A. glandulifera have longer lateral branches than other taxa of section Arachis, an upright mainstem, prostrate lateral branches, and larger flowers and seeds than other wild species in the section. The pods are greatly reticulated. Glandular trichomes are present on vegetative plant parts and the peg. Intraspecific hybrids among four accessions are fertile and uniformly have ten bivalents in pollen mother cells. Three accessions had nearly identical karyotypes, while a fourth had subtelocentric chromosomes 6 and 9. Hybrids between A. glandulifera and two other diploid species of section Arachis were male‐sterile, and chiasmata frequencies ranged between 5.8 and 12.1 per cell. Attempts to hybridize the species with A. hypogaea failed. A new species description and D genomic classification are proposed for A. glandulifera, which is different from previously described A and B genomes of section Arachis.

CYTOLOGICAL AND INTERFERTILITY RELATIONSHIPS OF ARACHIS SECTION ARACHIS

Twenty‐nine recently introduced diploid (2n = 2x = 20) accessions of section Arachis plus an A. correntina (Burk) Krap. et Greg. nom. nud. control were hybridized to the diploid A‐genome species A. duranensis Krap. et Greg. nom. nud. (ace. 7988), the diploid B‐genome species A. batizocoi Krap. et Greg. (acc. 9484), and with two subspecies of the A‐B genome (2n = 4x = 40) A. hypogaea cultivars NC 4 and Argentine. Most attempted crosses were successful and the resulting plants were vigorous. However, A. batizocoi × accession 30008 hybrids died as seedlings and A. batizocoi × accession 30017 produced only dwarf plants. The 710 diploid F1s from A. batizocoi were generally sterile, while those from A. duranensis had fertility ranges from 5% to 84%. Meiotic chromosome relationships in diploid crosses were cytologically evaluated in 185 plants plus tester accessions. Most taxa in section Arachis have an A genome, only A. batizocoi accessions have a B genome, a D genome is represented by accessions 30091 and 30099, and two other genomic groups, represented by accessions 30011 and 30033, may be present in the section. Most cytological differentiation was found among species originally collected in southern and eastern Bolivia. On the other hand, species collected at the extremes of the distribution of section Arachis species (northern Argentina to north‐central Brazil) were cytologically very similar. Evidence is presented for speciation in Arachis being associated with both genetic differentiation and with translocated chromosomes. All taxa in the section except the D‐genome species are believed to be cross‐compatible with A. hypogaea, so germplasm introgression from most Arachis species should be possible.

Utilization of wild relatives in the genetic improvement of Arachis hypogaea L.

Autotetraploids were established from 8 diploid wild species of section Arachis. In all the autotetraploids the chromosomes paired largely as bivalents even though they possess the ability to pair as multivalents. Pollen and pod fertility in the C1 generation were not directly associated with chromosome pairing. The C2 generation autotetraploids showed a gradual increase in bivalent associations and pollen and pod fertility. The identification of two genomes, A and B, in the diploid species and in the tetraploid, A. hypogaea, of the section Arachis, a fairly good crossability, and the type of chromosome associations observed in hybrids between A. hypogaea and the autotetraploids of wild Arachis species indicated good prospects of utilizing autotetraploids as genetic bridges in transferring desired traits from these taxa into groundnut.

A preliminary pachytene analysis of two species of Arachis L.

The morphology of pachytene chromosomes was studied in A. glabrata Benth. and A. pusilla Benth. belonging respectively to the sections Rhizomatosae and Triseminale. These two species can not be crossed with the cultivated groundnut A. hypogaea L. All 20 chromosomes of A. glabrata could be identified individually and further classified into 5 basic types. The features that enabled the identification of chromosomes were: total length, arm ratios, nucleolus attachment and position and extent of heterochromatin. A simple key has been proposed for classifying different chromosomes to facilitate their easy identification. The genomes of A. glabrata did not resemble those of A. hypogaea except for the presence of an 'A' chromosome, 2 euchromosomes and 2 nucleolus organisers. A. glabrata did not appear to be an amphidiploid but rather an allopolyploid hybrid. The genome of A. pusilla contained chromosomes unlike those of any other species of section Arachis. It was concluded that both these species are quite unrelated to other species of the section Arachis.

Utilisation of wild relatives in the genetic improvement of Arachis hypogaea L.

Cross-compatibility of species in section Arachis Krap. et Greg. nom. nud., and chromosome pairing and pollen fertility in their interspecific F1 hybrids were studied to further understand the phylogenetic relationships among these species. Except those with A. batizocoi Krap. et Greg. nom. nud., hybrids between diploid species have near normal bivalent frequency (9.1-9.8) and moderate to high pollen fertility (60-91%). Hybrids between A. batizocoi and other species have low bivalent frequency (5.2-6.9) and very low pollen fertility (3-7%). These results confirm the earlier separation of these species into two groups based on karyomorphology and Mahalanobis D(2) calculated on arm ratios. These studies also provide a picture of relative affinities between A. batizocoi, the lone member of one cluster, and the other species, and among the rest of the species. They also indicate that the basic chromosome complement in the two groups of species is the same. Chromosome pairing in triploid hybrids, (A. hypogaea L. X diploid wild species), suggests that A. batizocoi is the closest diploid relative of A. hypogaea. It is closer to A. hypogaea subspecies fastigiata Waldron than to A. hypogaea subspecies hypogaea Krap. et. Rig. Other diploid species of the section Arachis are equidistant from A. hypogaea, and have the same genome which has strong homology to one of the genomes of A. hypogaea. Based on the present results, the two tetraploid species, A. monticola Krap. et Rig. and A. hypogaea can be recognised as two forms of the same species. Breeding implications have been discussed in the light of chromosome behaviour observed in hybrids of A. hypogaea X diploid species, and on the presumptions that A. hypogaea has an AABB genomic constitution, and that among the diploid species, the 'B' genome is present in A. batizocoi while the 'A' genome is common to the other diploid species of section Arachis.

Photoperiodic Response of Peanut Species1

Abstract Many Arachis species collections do not produce pegs in North Carolina even though they flower profusely. To investigate reasons for the failure of fruiting, nine wild peanut species of section Arachis and three A. hypogaea cultivars representing spanish, valencia and virginia types were evaluated for response to short and long-day treatments in the North Carolina State Phytotron Unit of the Southeastern Environmental Laboratories. The objective of this investigation was to determine the flowering and fruiting responses of Arachis species to short and long-day photoperiods. Plant collections grown under a 9-hour short-day treatment were generally less vigorous, but produced more pegs than corresponding plants grown in long-day treatments which were produced by 9 hours of light plus a 3-hour interruption of the dark period. Annual species produced significantly more flowers and pegs than perennial species during both long and short days. The total number of flowers produced ranged from 0 during short days for A. correntina to more than 300 for A. cardenasii in long-day treatments. Only one plant of each species A. chacoense and A. villosa, and no plants of A. correntina, flowered in short days. Total numbers of pegs produced in short-day treatments were generally greater than in long-day treatments and the ratio of total number of pegs/total number of flowers was consistently greater during short-day treatments. A general trend was observed for more flowers produced in long-day treatments, but more pegs produced in short days. This study indicated that photoperiod can be manipulated to increase the seed set of some species and the success rate of obtaining certain interspecific hybrids. Furthermore, introgression from wild to cultivated species may possibly alter the reproductive capacity of A. hypogaea to photoperiod.

Hybrids in the Genus Arachis Between Sections Erectoides and Arachis1

The objective of this study was to determine whether diploid members of section Arachis could potentially be used as bridges between section Erectoides Krap. et. Greg. nom. nud. and A. hypogaea. Two diploid (2n = 20) taxa of section Erectoides and their F1 and F2C1 hybrids were evaluated. The female parent, A. rigonii Krap. et Greg. (PI 262142, collection no. GKP 10034), and male parent, A. sp. (PI 262278, collection no. GKP 9841) had perfect bivalent formation, but the F1 did not produce enough flowers to cytologically examine. The F2C1 averaged 2.76 univalents, 18.48 bivalents, 0.04 trivalents, and 0.04 quadrivalents per pollen mother cell and pairing of chromosomes between the two section Erectoides species is believed to be minimal. Hybrids between the F2C1 and the diploid section Arachis species A. stenosperma Greg. et Greg, nom. nud. (PI 338280, collection no. HLK 410) and A. duranensis Krap. et Greg. nom. nud. (PI 219823, collection no. K 7988) were studied. Multivalents were observed at a low frequency. Members of sections Erectoides and Arachis may have a common genome.The results indicate that gene transfer from section Erectoides species into the cultivated peanut seems possible by using diploid members of section Arachis as bridge species. Early metaphase I microsporocytes with an unreduced chromosome number were observed in three hybrids. Two fruits were recovered from intersectional colchicine‐treated hybrids, but the seeds were inviable. Future success in restoring fertility may depend on propagating large numbers of colchicine‐treated cuttings.

Cytology of Interspecific Hybrids in Section Arachis of Peanuts1

Abstract Interspecific hybrids between Avachis correntina (Burk.) Krap. et Greg. nom. nud. (coll. GKP 9530–31) and seven other diploid peanut species of section Arachis nom. nud. [syn. Axonomorphae (7)] were cytologically analyzed. Although hybrid plants were partially sterile, cytological barriers to gene exchange were nonexistent except for A. batizocoi Krap. et Greg, hybrids. Arachis batizocoi hybrids had between 0 and 4.67% pollen fertility, probably due to an average of 2.88 univalents per cell. Laggards and anaphase I bridges were observed in 85% of the hybrid cells. Because the cultigen, A. hypogaea L. (2n = 40), and the diploid wild species (2n = 20) are at different ploidy levels, hybridization results in sterile triploid plants. This is a major barrier to introgression from wild to cultivated varieties. In order to derive wild species of section Arachis at the same ploidy level as A. hypogaea, 572 three to six-day-old seedlings were colchicine-treated representing 34 interspecific Arachis section hybrid combinations. Eighty-one cytologically confirmed amphidiploids plus 49 probable ones based on plant morphology were isolated. After colchicine treatments, 26 autotetraploids were likewise produced from six species. The observations indicated that selection can occur at the diploid level in wild species for desired agronomic traits or for disease and insect resistances. Colchicine-treated selected hybrid seedlings would then serve as a pathway for overcoming the major sterility obstacle to introgressing germplasm into A. hypogaea.