Resistance to groundnut rosette disease in wild Arachis species

One hundred and sixteen accessions representing 28 species in the genus Arachis were evaluated for resistance to groundnut rosette disease using an infector row technique during the 1996/97, 1997/98, 1998/99 and 1999/2000 growing seasons at Chitedze, Malawi. Of these, a total of 25 accessions belonging to Arachis diogoi (1 accession), A. hoehnei (2), A. kretschmeri (2), A. cardenasii (2), A. villosa (1), A. pintoi (5), A. kuhlmannii (2), A. appressipila (3), A. stenosperma (5), A. decora (1), and A. triseminata (1) showed resistance to the groundnut rosette disease. No visible disease symptoms were observed in several accessions belonging to A. appressipila, A. cardenasii, A. hoehnei, A. kretschmeri, A. villosa, A. pintoi, A. kuhlmannii, and A. stenosperma. Some accessions in A. appressipila, A. diogoi, A. stenosperma, A. decora, A. triseminata, A. kretschmeri, A. kuhlmannii, and A. pintoi were resistant to all three components of rosette, Groundnut rosette ass is tor virus (GRAV), Groundnut rosette virus (GRV) and its satellite RNA (sat. RNA). Two accessions in A. stenosperma and one accession in A. kuhlmannii showed the presence of all three components of the rosette disease. Several wild Arachis accessions were resistant to GRAV. All the accessions of A. batizocoi (4), A. benensis (2), A. duranensis (46), A. dardani (1), A. ipaensis (1), A. magna (1), A. monticola (3), A. oteroi (1), A. pusilla (4), and A. valida (2) were susceptible to rosette disease. In all these accessions, infected plants were chlorotic and severely stunted. The value of exploitation of the resistance in wild Arachis species in rosette resistance breeding programmes is discussed.     

Sequence Diversity of the Nucleoprotein Gene of Peanut bud necrosis virus Isolates from South India

Peanut bud necrosis virus (PBNV), genus Tospovirus (family Bunyaviridae), is an important virus infecting peanut and other crops in South India. PBNV isolates naturally infecting groundnut, brinjal, tomato, black gram, field bean, cowpea, cotton, jute, taro and Calotropis plants were collected from different regions of South India and characterized. Infection was confirmed by direct antigen‐coating enzyme‐linked immunosorbent assay (DAC‐ELISA) using PBNV‐specific antiserum. The coat protein gene was further amplified using PBNV coat protein‐specific primers. The amplicon (830 bp) was cloned and sequenced; sequence analysis revealed that the N gene shared 93–100% and 95–100% sequence identity with PBNV at the nucleotide and amino acid levels, respectively.     

A large scale analysis of resistance gene homologues in<Emphasis Type="Italic"> Arachis</Emphasis>

Arachis hypogaea L., commonly known as the peanut or groundnut, is an important and widespread food legume. Because the crop has a narrow genetic base, genetic diversity in A. hypogaea is low and it lacks sources of resistance to many pests and diseases. In contrast, wild diploid Arachis species are genetically diverse and are rich sources of disease resistance genes. The majority of known plant disease resistance genes encode proteins with a nucleotide binding site domain (NBS). In this study, degenerate PCR primers designed to bind to DNA regions encoding conserved motifs within this domain were used to amplify NBS-encoding regions from Arachis spp. The Arachis spp. used were A. hypogaea var. Tatu and wild species that are known to be sources of disease resistance: A. cardenasii, A. duranensis , A. stenosperma and A. simpsonii. A total of 78 complete NBS-encoding regions were isolated, of which 63 had uninterrupted ORFs. Phylogenetic analysis of the Arachis NBS sequences derived in this study and other NBS sequences from Arabidopsis thaliana, Medicago trunculata , Glycine max , Lotus japonicus and Phaseolus vulgaris that are available in public databases This analysis indicates that most Arachis NBS sequences fall within legume-specific clades, some of which appear to have undergone extensive copy number expansions in the legumes. In addition, NBS motifs from A. thaliana and legumes were characterized. Differences in the TIR and non-TIR motifs were identified. The likely effect of these differences on the amplification of NBS-encoding sequences by PCR is discussed.Electronic Supplementary Material Supplementary material is available for this article if you access the article at . A link in the frame on the left on that page takes you directly to the supplementary material.Communicated by M.-A. Grandbastien     

Restriction fragment length polymorphism evaluation of six peanut species within the Avachis section

Summary Restriction fragment length polymorphisms (RFLP) were assessed among accessions within six peanut species of the Arachis section: tetraploid cultivated species, A. hypogaea; tetraploid wild species, A. monticola; and four diploid wild species, A. batizocoi,A. cardenasii, A. duranensis and A. glandulifera. While the two tetraploid species did not show polymorphism with 16 PstI-generated random genomic probes, two of seven seed cDNA probes detected polymorphisms. The RFLP variation detected by two seed cDNA probes appeared to be related to structural changes occurring within tetraploid species. The botanical var. fastigiata (Valencia market type) of A. hypogaea subspecies fastigiata was shown to be the most variable. Arachis monticola was found to be more closely related to A. hypogaea subspecies hypogaea than to subspecies fastigiata. Diploid species A. cardenasii, A. duranensis, and A. glandulifera showed considerable intraspecific genetic diversity, but A. batizocoi showed little polymorphism. The genetic distance between the cultivated peanut and wild diploid species was found to be closest for A. duranensis.Florida Agricultural Experiment Station, Journal Series No. R-01493     

Peanut yellow spot virus: A distinct tospovirus species based on serology and nucleic acid hybridisation

Nucleocapsids of peanut yellow spot virus (PYSV), purified from peanut (= groundnut) plant tissue, contained a protein with a molecular mass of 29 kDa. In ELISA and immuno-blot analysis the virus did not react with tomato spotted wilt virus (TSWV), Impatiens necrotic spot virus (INSV) and peanut bud necrosis virus (PBNV) antisera. PYSV contained three RNA species, a large (L) RNA (c.8900 nucleotides), a medium (M) RNA (c.4800 nucleotides) and a small (S) RNA (c.3000 nucleotides), similar to other tospoviruses. In addition, a fourth RNA species of approximately 1800 nucleotides was also present in purified preparations. Hybridisation analysis under high stringency conditions revealed no hybridisation between PYSV RNAs and cDNA probes representing the nucleocapsid (N) gene, the glycoprotein (GP) gene and the 3' half of the RNA polymerase gene of PBNV. PYSV genomic RNAs also failed to hybridise with cDNA probes from the GP genes of TSWV and INSV. In reciprocal tests, the cDNA clones of PYSV S and M RNAs did not hybridise with any of the PBNV RNAs. Based on the absence of serological relationships between PYSV and PBNV, TSWV and INSV and lack of nucleotide homology based on hybridisation studies between the PYSV RNAs and cDNA clones from PBNV, TSWV and INSV, PYSV should be considered as a distinct species of the genus Tospovirus under a new serogroup, putatively designated ‘V’.     

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.     

A single dominant gene for Fusarium wilt resistance in protoplast-derived tomato plants

Summary 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.Submitted as Journal Article No. 516 by International Crops Research Institute for the Semi-Arid Tropics (ICRISAT)     

Diversity of seed storage protein patterns in wild peanut (Arachis,Fabaceae) species

55 accessions of wild peanuts (Arachis spp.) introduced from South America were analyzed for seed storage protein composition using SDS-PAGE electrophoresis. The objectives of the study were to evaluate variability within sect.Arachis and to classify taxa based on protein composition. 25 different band positions were resolved. Individual accessions had 11 to 18 bands which included the conarachin region (MW > 50 kD), two to five bands in the acidic arachin region (MW 38–49.9 kD), three to seven in the intermediate MW region (23 to 37.9 kD), two to five bands in the basic arachin region (18–22.9 kD), and one to three bands in the low MW protein region (14–17.9 kD). These data were utilized in a principal coordinate analysis based on the matrix of genetic distances between all pairs of the 55 accessions. Several groups of accessions conformed to expected species classification includingA. batizocoi, A. stenosperma, andA. monticola; whileA. duranensis, A. cardenasii, A. helodes, andA. correntina did not form good groups. The study showed that great diversity exists for protein profiles and seed storage proteins have potential for aiding species classification and for serving as markers for interspecific hybridization studies.     

Abundant Microsatellite Diversity and Oil Content in Wild Arachis Species

The peanut (Arachis hypogaea) is an important oil crop. Breeding for high oil content is becoming increasingly important. Wild Arachis species have been reported to harbor genes for many valuable traits that may enable the improvement of cultivated Arachis hypogaea, such as resistance to pests and disease. However, only limited information is available on variation in oil content. In the present study, a collection of 72 wild Arachis accessions representing 19 species and 3 cultivated peanut accessions were genotyped using 136 genome-wide SSR markers and phenotyped for oil content over three growing seasons. The wild Arachis accessions showed abundant diversity across the 19 species. A. duranensis exhibited the highest diversity, with a Shannon-Weaver diversity index of 0.35. A total of 129 unique alleles were detected in the species studied. A. rigonii exhibited the largest number of unique alleles (75), indicating that this species is highly differentiated. AMOVA and genetic distance analyses confirmed the genetic differentiation between the wild Arachis species. The majority of SSR alleles were detected exclusively in the wild species and not in A. hypogaea, indicating that directional selection or the hitchhiking effect has played an important role in the domestication of the cultivated peanut. The 75 accessions were grouped into three clusters based on population structure and phylogenic analysis, consistent with their taxonomic sections, species and genome types. A. villosa and A. batizocoi were grouped with A. hypogaea, suggesting the close relationship between these two diploid wild species and the cultivated peanut. Considerable phenotypic variation in oil content was observed among different sections and species. Nine alleles were identified as associated with oil content based on association analysis, of these, three alleles were associated with higher oil content but were absent in the cultivated peanut. The results demonstrated that there is great potential to increase the oil content in A. hypogaea by using the wild Arachis germplasm.     

Additional sources of resistance to groundnut rosette disease in groundnut germplasm and breeding lines

Groundnut rosette, a virus disease of groundnut (Arachis hypogaea) transmitted by the aphid, Aphis craccivora Koch, reduces yield in susceptible cultivars by 30–100%. Additional sources were sought in germplasm accessions involving 2301 lines from different sources and from 252 advanced breeding lines derived from crosses involving earlier identified sources of resistance to rosette. The lines were evaluated in field screening trials using an infector row technique during 1996 and 1997 growing seasons. Among the germplasm lines, 65 accessions showed high levels of resistance while 134 breeding lines were resistant. All rosette disease resistant lines were susceptible to groundnut rosette assistor virus. This work identified germplasm and breeding lines that will contribute to an integrated management of groundnut rosette disease. These new sources also provide an opportunity to eliminate yield losses due to the rosette disease.     

Combining ability for resistance in peanut (Arachis hypogaea) to Peanut bud necrosis tospovirus (PBNV)

The combining abilities of field resistance to peanut bud necrosis disease (PBND) caused by Peanut bud necrosis tospovirus (PBNV) were examined to understand the type of gene action governing resistance to the disease, and to identify peanut lines suitable for use as parents in a PBND‐resistance breeding programme. The Ft and F2 progenies from a six‐parent diallel cross and their parents were evaluated under field conditions. They were assessed for disease incidence at 30, 40, 50 and 60 days after planting (DAP), and reactions of the lines to the disease could be best differentiated at 50 and 60 DAP. Results indicated highly significant general combining ability (GCA) effects for PBND incidence in F₁ and F₂ generations. Specific combining ability (SCA) and reciprocal effects were also found to be significant, but their relative contributions to variation among crosses were much less than those of GCA effects. These results suggested that the type of gene action governing resistance to PBND was mainly additive, and selection for PBND resistance in these populations should be effective. Strong correlation coefficients between parental means and GCA effects for disease incidence were seen in both Ft and F2 generations, suggesting that per se performance of the parental line could be used as a predictor of the capability of the line to transmit its PBND‐resistant attribute to progenies. The reciprocal effects were in favour of using resistant lines as female parents. The peanut lines ICGV 86388, 1C 10 and 1C 34 were found to be suitable for use in a PBND–resistance breeding programme.     

RFLP variability in peanut (Arachis hypogaea L.) cultivars and wild species

Summary RFLP variability was studied in eight U.S. peanut cultivars, representing the four market types, and in 14 wild Arachis species accessions, using random genomic clones from a PstI library. Very low levels of RFLP variability were found among the allotetraploids, which included the U.S. cultivars and Arachis monticola, a wild species. The diploid wild species were very diverse, however. RFLP patterns of the allotetraploids were more complex than the diploids, and the two constituent genomes could usually be distinguished. On the basis of RFLP band sharing, A. ipaensis, A. duranensis, and A. spegazzinii appeared most closely related to the diploid progenitor species of the allotetraploids. A dendrogram of relationships among the diploid wild species was constructed based on band sharing.     

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

Summary The chromosome complements of 12 taxa in section Arachis were karyotypically and meiotically analysed. In taxa with 2n=20 the arm ratio of the respective pair of chromosomes was taken as an independent quantitative character and statistically analysed by Mahalanobis D². Two clusters were formed, one represented solely by A. batizocoi and the other consisting of the remaining 11 taxa. This grouping was confirmed by canonical analysis. In the larger group of species, A villosa and A. correntina were closely related karyotypically and on D² distance, while A. cardenasii forms a distinct subgroup. A. cardenasii lacks the short A chromosome recorded in other species of this group, and A. batizocoi is no longer the only species to have a pair of chromosomes with a secondary constriction. The taxa with 2n=40, A. monticola and A. hypogaea, are karyotypically very similar, though there is a difference in the number of chromosome pairs with a secondary constriction. On the basis of karyomorphological affinity, especially in relation to marker chromosomes, A. cardenasii is probably one of the ancestors of the tetraploid species studied.Approved as ICRISAT Journal Article No. 169 and released for publication     

Genetic relationships between peanut and wild species ofArachis sect.Arachis (Fabaceae): Evidence from RAPDs

Twenty-six accessions of wildArachis species and domesticated peanuts,A. hypogaea, introduced from South America were analyzed for random amplified polymorphic DNA (RAPD). The objective of the study was to investigate inter- and intraspecific variation and affinities among species of sect.Arachis which have been proposed as possible progenitors for the domesticated peanut. Ten primers resolved 132 DNA bands which were useful for separating species and accessions. The most variation was observed among accessions ofA. cardenasii andA. glandulifera whereas the least amount of variation was observed inA. hypogaea andA. monticola. The two tetraploid species could not be separated by using RAPDs.Arachis duranensis was most closely related to the domesticated peanut and is believed to be the donor of the A genome. The data indicated thatA. batizocoi, a species previously hypothesized to contribute the B genome toA. hypogaea, was not involved in its evolution. The investigation showed that RAPDs can be used to analyze both inter- and intraspecific variation in peanut species. Southern hybridization of RAPD probes to blots containing RAPD of theArachis species provided information on genomic relationships and revealed the repetitive nature of the amplified DNA.     

Identification of peanut (Arachis hypogaea L.) RAPD markers diagnostic of root-knot nematode (Meloidogyne arenaria (Neal) Chitwood) resistance

DNA markers linked to a root-knot nematode resistance gene derived from wild peanut species have been identified. The wild diploid peanut accessions K9484 (Arachis batizocoi Krapov. & W. C. Gregory), GKP10017, (A. cardenasii Krapov & W. C. Gregory), and GKP10602 (A. diogoi Hoehne) possess genes for ressitance to Meloidogyne arenaria. These three accessions and A. hypogaea cv. Florunner were crossed to generate the hybrid resistant breeding line TxAg-7. This line was used as donor parent to develop a BC₄F₂ population segregating for resistance. Three RAPD markers associated with nematode resistance were identified in this population by bulked segregant analysis. Linkage was confirmed by screening 21 segregatingh BC₄F₂ and 63 BC₅F₂ single plants. Recombination between marker RKN410 and resistance, and between marker RKN440 and resistance, was estimated to be 5.4±1.9% and 5.8±2.1%, respectively, on a per-generation basis. These two markers identified a resistance gene derived from either A. cardenasii or A. diogoi, and were closely linked to each other. Recombination between a third marker, RKN229, inherited from A. cardenasii or A. diogoi, and resistance was 9.0±3.2% per generation. Markers RKN410 and RKN229 appeared to be linked genetically and flank the same resistance gene. All markers were confirmed by hybridization of cloned or gel-purified marker DNA to blots of PCR-amplified DNA. Pooled data on the segregation of BC₅F₂ plants was consistent with the presence of one resistance gene in the advanced breeding lines. Different distributions of resistance in the BC₅F₂ progeny and TxAG-7 suggest the presence of additional resistance genes in TxAG-7.     

Screening additional wild tomatoes for resistance to the whitefly-borne tomato yellow leaf curl virus

Plants of 25 wild Lycopersicon accessions were screened in the greenhouse for resistance to the whitefly-borne tomato yellow leaf curl virus (TYLCV). High levels of resistance were detected in 7 of 9 accessions of L. peruvianum and in all 5 accessions of L. chilense tested. In contrast, plants of 7 accessions of L. hirsutum and 3 of 4 accessions of L. pimpinellifolium were highly susceptible. Plants of accession CIAS 27 (L. pimpinellifolium) showed moderate resistance to TYLCV.     

Flow cytometric analysis for ploidy level differentiation of 45 hairy vetch accessions

Determining the ploidy of plant germplasm is a necessary step in breeding or genetic studies in species. The purpose of this research was to determine the presence of ploidy level differentiation of hairy vetch (Vicia villosd) germplasm. Flow cytometry and root tip chromosome squashing methods were employed to assess 45 accessions labeled V. villosa available through the USDA germplasm collection. Flow cytometry determined that 43 of the accessions were 2C, one accession was 4C, and one accession was 6C. Analysis of accessions by root tip chromosome counts indicated that all accessions were diploid. The 2C accession contains 14 chromosomes and their chromosomes were approximately one-half and one-third in size as compared to the chromosomes of the 4C and 6C accessions, respectively. The 4C accession was observed to have 16 chromosomes and the 6C accession was observed to have 14 chromosomes. The large-scale differences in DNA amounts were due to chromosomal size variability as opposed to ploidy differences. This revealed the incidence of species misidentification of these two V. villosa accessions to be Vicia pannonica. All the V. villosa accessions were observed to be diploid and have similar DNA amounts. Flow cytometry proved to be useful in the efficient assessment of these accessions.     

Genetic relationships among seven sections of genus <Emphasis Type="Italic">Arachis</Emphasis>studied by using SSR markers

Background  

The genus Arachis, originated in South America, is divided into nine taxonomical sections comprising of 80 species. Most of the Arachis species are diploids (2n = 2x = 20) and the tetraploid species (2n = 2x = 40) are found in sections Arachis, Extranervosae and Rhizomatosae. Diploid species have great potential to be used as resistance sources for agronomic traits like pests and diseases, drought related traits and different life cycle spans. Understanding of genetic relationships among wild species and between wild and cultivated species will be useful for enhanced utilization of wild species in improving cultivated germplasm. The present study was undertaken to evaluate genetic relationships among species (96 accessions) belonging to seven sections of Arachis by using simple sequence repeat (SSR) markers developed from Arachis hypogaea genomic library and gene sequences from related genera of Arachis.     

Immunochemical characterization of seed proteins of some species of the genusArachis L.

Relationships between seed protein patterns of 16 species ofArachis were studied by means of immunochemical methods (immunoelectrophoresis and double diffusion). The broad similarity of these patterns suggests that protein patterns are conservative in this genus from an evolutionary viewpoint. The differences which have evolved support recent schemes for classifying the genus, particularly the breakdown into sections. It also suggests thatA. villosa andA. correntina should probably be recognized as distinct species. The strong relationship indicated betweenA. hypogaea andA. batizocoi supports the hypothesis that the latter may be source of one of the genomes ofA. hypogaea. The possibility thatA. cardenasii might be the source of the other genome did not receive such strong positive support.