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Abstract

Male sterile (MS) plants fail to produce functional anthers, pollen, or male gametes. This condition is useful in sunflower hybrid seed production. A MS form identified in an invasive population of H. annuus located in Las Malvinas was characterized by 37 morphological variables, six mitochondrial genes (atpA, atp6, coxIII, orfb, orfB and orfC) associated with cytoplasmic male sterility (CMS), five SSR loci associated with ms9, ms10, and ms11 nuclear male sterility genes, and the HRGO2 marker associated with the Rf1 fertility restoration gene for CMS-PET1. Restoration of MS condition was evaluated through crosses with 13 sunflower inbred lines. Las Malvinas site was described regarding its population size, spatial distribution, and male sterility occurrence. Ten years after the first observation, population size was over 250,000 individuals. The adoption of this species as ornamental plant in home gardens has contributed its expansion. The low frequency of MS plants found in natural conditions (0.4 %) is concordant with a CMS form in combination with restoration genes. Wild individuals harboring the CMS-PET1 cytoplasm and individuals carrying a different mitochondrial genome were found. The Rf1 restorer gene for CMS-PET1 was not detected. The new type of male sterility was different than CMS-PET1 in pollen morphology; absence of orfC; and different response to crosses with inbred lines. Molecular differences were found with CMS-RES1 and CMS-MAX1. The male sterility could not be explained by differences in the cytoplasmic or nuclear regions studied. The new MS form will expand the genetic diversity available for commercial hybrid sunflower production.

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... In plants, the phenomenon of cytoplasmic male sterility (CMS) stems from interaction between mitochondrial and nuclear genomes resulting in microsporogenesis disorders (Touzet & Meyer, 2014). All known natural CMSs, as well as most of the artificially obtained examples, are characterized by a special type of mitochondrial DNA (mtDNA) with numerous structural rearrangements as compared to the mtDNA of the fertile plants of the same species (Ivanov & Dymshits, 2007;Horn, Gupta & Colombo, 2014;Garayalde et al., 2015). The mitochondrial genomes of higher plants have comparatively large sizes with a multitude of noncoding and repetitive sequences that can result in the complex of sub-genomic structures (Chen & Liu, 2014). ...
... To create new CMS-Rf systems, prevent mtDNA unification, and reduce genetic vulnerability of sunflower hybrids to biotic and abiotic stresses, it is urgent to search for and introduce the new CMS sources into sunflower breeding. Although more than 70 cytoplasmic male sterility types have been identified in sunflower (Garayalde et al., 2015), they have not been sufficiently studied, resulting in limitation of their use in commercial hybrid breeding. Undoubtedly, research on the cytoplasmic male sterility phenomenon is important for investigating the fundamental problem of nuclear-cytoplasmic interaction in the ontogeny of higher plants (Hanson & Bentolila, 2004). ...
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Background Cytoplasmic male sterility (CMS) is a common phenotype in higher plants, that is often associated with rearrangements in mitochondrial DNA (mtDNA), and is widely used to produce hybrid seeds in a variety of valuable crop species. Investigation of the CMS phenomenon promotes understanding of fundamental issues of nuclear-cytoplasmic interactions in the ontogeny of higher plants. In the present study, we analyzed the structural changes in mitochondrial genomes of three alloplasmic lines of sunflower ( Helianthus annuus L.). The investigation was focused on CMS line PET2, as there are very few reports about its mtDNA organization. Methods The NGS sequencing, de novo assembly, and annotation of sunflower mitochondrial genomes were performed. The comparative analysis of mtDNA of HA89 fertile line and two HA89 CMS lines (PET1, PET2) occurred. Results The mtDNA of the HA89 fertile line was almost identical to the HA412 line ( NC_023337 ). The comparative analysis of HA89 fertile and CMS (PET1) analog mitochondrial genomes revealed 11,852 bp inversion, 4,732 bp insertion, 451 bp deletion and 18 variant sites. In the mtDNA of HA89 (PET2) CMS line we determined 27.5 kb and 106.5 kb translocations, 711 bp and 3,780 bp deletions, as well as, 5,050 bp and 15,885 bp insertions. There are also 83 polymorphic sites in the PET2 mitochondrial genome, as compared with the fertile line. Discussion The observed mitochondrial reorganizations in PET1 resulted in only one new open reading frame formation ( orfH522 ), and PET2 mtDNA rearrangements led to the elimination of orf777 , duplication of atp6 gene and appearance of four new ORFs with transcription activity specific for the HA89 (PET2) CMS line— orf645 , orf2565 , orf228 and orf285 . Orf228 and orf285 are the atp9 chimeric ORFs, containing transmembrane domains and possibly may impact on mitochondrial membrane potential. So orf228 and orf285 may be the cause for the appearance of the PET2 CMS phenotype, while the contribution of other mtDNA reorganizations in CMS formation is negligible.
... In plants, the phenomenon of cytoplasmic male sterility (CMS) stems from interaction between mitochondrial and nuclear genomes resulting in microsporogenesis disorders (Touzet & Meyer, 2014). All known natural CMSs, as well as most of the artificially obtained examples, are characterized by a special type of mitochondrial DNA (mtDNA) with numerous structural rearrangements as compared to the mtDNA of the fertile plants of the same species (Ivanov & Dymshits, 2007;Horn, Gupta & Colombo, 2014;Garayalde et al., 2015). The mitochondrial genomes of higher plants have comparatively large sizes with a multitude of noncoding and repetitive sequences that can result in the complex of sub-genomic structures (Chen & Liu, 2014). ...
... To create new CMS-Rf systems, prevent mtDNA unification, and reduce genetic vulnerability of sunflower hybrids to biotic and abiotic stresses, it is urgent to search for and introduce the new CMS sources into sunflower breeding. Although more than 70 cytoplasmic male sterility types have been identified in sunflower (Garayalde et al., 2015), they have not been sufficiently studied, resulting in limitation of their use in commercial hybrid breeding. Undoubtedly, research on the cytoplasmic male sterility phenomenon is important for investigating the fundamental problem of nuclear-cytoplasmic interaction in the ontogeny of higher plants (Hanson & Bentolila, 2004). ...
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Background . Cytoplasmic male sterility (CMS) is a common phenotype in higher plants, which often is associated with rearrangements in mitochondrial DNA (mtDNA), and is widely used to produce hybrid seeds in a variety of valuable crop species. The CMS phenomenon investigations are also promote understanding of a fundamental issue of nuclear-cytoplasmic interactions in the ontogeny of higher plants. In the present study, we analyzed the structural changes in mitochondrial genomes of three alloplasmic lines of sunflower (Helianthus annuus). The investigation was focused on CMS line PET2, as there are very few reports about its mtDNA organization. Methods . The NGS sequencing, de novo assembly, and annotation of sunflower mitochondrial genomes were performed. The comparative analysis of mtDNA of HA89 fertile line and two HA89 CMS lines (PET1, PET2) occurred. Results. The mtDNA of the HA89 fertile line was almost identical to the HA412 line (NC_023337). The comparative analysis of HA89 fertile and CMS (PET1) analog mitochondrial genomes revealed 11852 bp inversion, 4732 bp insertion, and 18 variant sites. In mtDNA of HA89 (PET2) CMS line 5050 bp and 5.9 kb insertions, as well as 0.95 kb and 3.8 kb deletions, were determined. There are also revealed 83 polymorphic sites in the PET2 mitochondrial genome, as compared with the fertile line. Discussion. Among the revealed rearrangements the 5.9 kb insertion results in putative orf1053 – coxI-atp6 chimeric protein, which could be the main reason for CMS phenotype development, whereas the role of other mtDNA reorganizations in CMS formation is negligible.
... Genetic basis of cytoplasmic male sterility is formed by structural rearrangements of mitochondrial DNA (mtDNA) [12][13][14]. New chimeric ORFs in the mtDNA of CMS lines are formed from fusion of known functional mitochondrial genes with uncharacteristic DNA sequences [1,12,15]. ...
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Background More than 70 cytoplasmic male sterility (CMS) types have been identified in Helianthus, but only for less than half of them, research of mitochondrial organization has been conducted. Moreover, complete mitochondrion sequences have only been published for two CMS sources – PET1 and PET2. It has been demonstrated that other sunflower CMS sources like MAX1, significantly differ from the PET1 and PET2 types. However, possible molecular causes for the CMS induction by MAX1 have not yet been proposed. In the present study, we have investigated structural changes in the mitochondrial genome of HA89 (MAX1) CMS sunflower line in comparison to the fertile mitochondrial genome. Results Eight significant major reorganization events have been determined in HA89 (MAX1) mtDNA: one 110 kb inverted region, four deletions of 439 bp, 978 bp, 3183 bp and 14,296 bp, respectively, and three insertions of 1999 bp, 5272 bp and 6583 bp. The rearrangements have led to functional changes in the mitochondrial genome of HA89 (MAX1) resulting in the complete elimination of orf777 and the appearance of new ORFs - orf306, orf480, orf645 and orf1287. Aligning the mtDNA of the CMS sources PET1 and PET2 with MAX1 we found some common reorganization features in their mitochondrial genome sequences. Conclusion The new open reading frame orf1287, representing a chimeric atp6 gene, may play a key role in MAX1 CMS phenotype formation in sunflower, while the contribution of other mitochondrial reorganizations seems to appear negligible for the CMS development. Electronic supplementary material The online version of this article (10.1186/s12870-019-1637-x) contains supplementary material, which is available to authorized users.
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Analyses of speciation genes--genes that contribute to the cessation of gene flow between populations--can offer clues regarding the ecological settings, evolutionary forces and molecular mechanisms that drive the divergence of populations and species. This review discusses the identities and attributes of genes that contribute to reproductive isolation (RI) in plants, compares them with animal speciation genes and investigates what these genes can tell us about speciation. Forty-one candidate speciation genes were identified in the plant literature. Of these, seven contributed to pre-pollination RI, one to post-pollination, prezygotic RI, eight to hybrid inviability, and 25 to hybrid sterility. Genes, gene families and genetic pathways that were frequently found to underlie the evolution of RI in different plant groups include the anthocyanin pathway and its regulators (pollinator isolation), S RNase-SI genes (unilateral incompatibility), disease resistance genes (hybrid necrosis), chimeric mitochondrial genes (cytoplasmic male sterility), and pentatricopeptide repeat family genes (cytoplasmic male sterility). The most surprising conclusion from this review is that identities of genes underlying both prezygotic and postzygotic RI are often predictable in a broad sense from the phenotype of the reproductive barrier. Regulatory changes (both cis and trans) dominate the evolution of pre-pollination RI in plants, whereas a mix of regulatory mutations and changes in protein-coding genes underlie intrinsic postzygotic barriers. Also, loss-of-function mutations and copy number variation frequently contribute to RI. Although direct evidence of positive selection on speciation genes is surprisingly scarce in plants, analyses of gene family evolution, along with theoretical considerations, imply an important role for diversifying selection and genetic conflict in the evolution of RI. Unlike in animals, however, most candidate speciation genes in plants exhibit intraspecific polymorphism, consistent with an important role for stochastic forces and/or balancing selection in development of RI in plants.
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Helianthus annuus is an invasive alien species naturalised in the central region of Argentina where it shares an extended area with the sunflower crop. As this species has also invaded several other sunflower crop growing areas in the world, it severely restricts the use of new technologies, for example herbicide tolerance by genetic modification. The natural seed dormancy of the wild Helianthus strains from the centre of origin in North America is well known, but the seed dormancy of the invasive biotypes is still unknown. Dormancy is a fitness trait related to the establishment, dispersion and persistence of invasive weeds. Four experiments were designed to investigate the effect of the pericarp, light, temperature, the after-ripening period and hybridization with the DK3880CL sunflower crop (F1) on the seed dormancy of five invasive H. annuus biotypes. The results showed that pericarp scarification increased imbibition of the whole achene by 19%. Light stimulation only increased germination in the wild biotype without any effect on the domesticated sunflower. A period of 12 months after-ripening at 5°C reduced seed dormancy in the wild biotype and its progeny; the optimal temperature for seed germination at this period was found to be 15°C. Mechanical scarification was the best treatment for overcoming seed dormancy with a differential germination, in the biotypes with the highest response, superior to 63%. Hybridization with domesticated sunflower had a minimal or no effect on seed dormancy but the germination rate was improved in three F1 crosses. Wild biotype dormancy appears to be governed by the maternal pericarp and intrinsic hormone regulation. An increased germination rate of some progenies could constitute an advantage during seedling establishment but only in winters without any frost.
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Anthers of inbred F44 fertile (N) and cytoplasmic male-sterile (T) corn plants (Zea mays L.) were compared cytologically. No differences between fertile and sterile anthers were observed in size and number of mitochondria or plastids until after the start of anther degeneration. A rapid division of mitochondria was observed, however, in the tapetum and sporogenous cells of both fertile and sterile anthers during early growth stages. This rapid increase in mitochondrial numbers per cell (some 20to 40-fold) preceded tapetal breakdown in sterile anthers and did not occur in other anther cells or in plastids. Limited observations on the megagametophyte and nucellus revealed that mitochondria in ovules remain relatively constant in size and number during gametogenesis and do not undergo degeneration. DIFFERENCES in number and size of mitochondria were observed at the various growth stages and in the different tissues during the electron microscope studies that demonstrated early breakdown of tapetal mitochondria in male-sterile corn anthers (Lee, 1976; Warmke and Lee, 1977). Some apparent differences also were noted in plastid size. For these reasons, and because of a possible relationship to male sterility, measurements and counts of these organelles were made as described in the following sections. MATERIALS AND METHODS-Tissue preparation-Anthers of inbred F44 maintainer corn lines (Zea mays L.) and their T cytoplasmic male-sterile counterparts were collected from the field at Gainesville, Florida. The anthers were removed, fixed, embedded, and mounted as reported in earlier ultrastructural studies (Warmke and Lee, 1977). The same procedures for sectioning and staining also were used. In the present studies,
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Cultivated hybrid sunflower (Helianthus annuus L.) production depends on a single male-sterile cytoplasm, PET1, derived from H. petiolaris Nutt. and a few fertility restoration genes. This study was conducted to locate new restoration genes for the PET1 cytoplasm from the wild species of the genus Helianthus. Ten wild species populations from the USA were grown in a field nursery and crossed with cytoplasmic male-sterile inbred line cmsHA 89 to determine the presence and inheritance of restoration genes in wild annual and perennial species. Standard sunflower breeding techniques were used to obtain F 1 and B 1 CF 1 seed, whereas F 2 seed was produced by sibbing F 1 plants instead of selfing due to the low self-compatibility. All H. annuus L., H. argophyllus T. & G., H. praecox ssp. runyonii Heiser, and H. tuberosus L. populations possessed dominant fertility restoration genes at high frequencies, varying from 57 to 100% [...]
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Nuclear male sterility (NMS) conditioned by recessive genes provides a useful tool for sunflower (Helianthus annuus L.) breeding and genetics programs. The objectives of this study were to evaluate seven induced NMS mutants derived from inbred line HA 89 and two lines, B11A3 and P21, for their mode of inheritance, allelic relationships, and agronomic characteristics. Self-pollinated F 2 progenies from heterozygous F 1 male-fertile (MF) plants and BC 1 F 1 progenies from crossing male-sterile (MS) with F 1 heterozygous MF plants segregated in ratios of three MF to one MS and one MF to one MS, respectively, indicating single recessive gene control of male sterility(.)
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To study the molecular basis of cytoplasmic male sterility (CMS) in sunflower (Helianthus annuus), we compared the physical organization and transcriptional properties of mitochondrial DNAs (mtDNAs) from isonuclear fertile and CMS lines. Mapping studies revealed much greater similarity between the two mtDNAs than in previous comparisons of fertile and CMS lines from other plant species. The two sunflower mtDNAs 1) are nearly identical in size (300 kb and 305 kb); 2) contain the same 12 kb recombination repeat and associated tripartite structure; 3) have the same dispersed distribution of mitochondrial genes and chloroplast DNA-homologous sequences; 4) are greater than 99.9% identical in primary sequence; and 5) are colinear over a contiguous region encompassing 94% of the genome. Detectable alterations are limited to a 17 kb region of the gename and reflect as few as two mutations - a 12 kb inversion and a 5 kb insertion/deletion. One endpoint of both rearrangements is located within or near atpA, which is also the only mitochondrial gene whose transcripts differ between the fertile and CMS lines. Furthermore, a nuclear gene that restores fertility to CMS plants specifically influences the pattern of atpA transcripts. Rearrangements at the atpA locus may, therefore, be responsible for CMS in sunflower.
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Commercial sunflower hybrids have been produced by means of a single male-sterile Helianthus petiolaris Nutt. cytoplasm and a few fertility restoration genes. The objectives of this study were to characterize cytoplasmic male-sterility (cms) systems in wild H. annuus L. accessions (PI413178 and PI 413180) and to determine the inheritance of fertility restoration. Male-sterile plants were identified and maintained by backcrossing with inbred line HA89. Male-fertile progenies from crosses between cms plants of the two PIs and USDA inbred lines indicated the presence of fertility restoration genes in P21, RMAX1, and PI 413178 for cms PI 413178 (cms-ANN2), and P21, RHA280, RHA801, RPET2, and PI 413180 for cms PI 413180 (cms-ANN3). All heterozygous male-fertile plants of backcross progenies, except for RHA280, crossed to cms plants resulted in a segregation ratio of one male-fertile to one male sterile, indicating a single dominant gene controlling fertility restoration. The backcross progeny of cms PI 413180/HA89//cms PI 413180/RHA280 had a segregation ratio of one male-fertile to three male sterile, suggesting two complementary dominant genes for fertility restoration. Pollinating male-fertile plants of both accessions with HA89 pollen resulted in male-fertile and male-sterile F 1 plants, suggesting the existence of male-sterile cytoplasm and heterozygosity for restoration genes in the male-fertile plants. In field tests, male-sterile PI 413178/4 * HA89 and PI 413180/ 4 * HA89 plants produced no seed after self-pollination, and 95 and 98% seed set, respectively, under open-pollination indicating complete male-sterility and female fertility. The new cms sources from wild H. annuus and corresponding fertility restoration genes provide diversity for sunflower hybrid production.
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and an anthocyanin pigment gene (T) by Leclercq (1966) facilitated preanthesis elimination of fertile red plants and Nuclear male sterility (NMS) is a useful tool for sunflower (Helian- made sunflower hybrid production feasible using NMS. thus annuus L.) breeding and genetics programs. A clear understand- ing ofthe geneticsof NMSat themolecular leveland theidentification Consequently, NMS was used for commercial hybrid seed of linked molecular markers will greatly facilitate breeding for this production in several European countries in the early trait. P21 is an inbred line carrying the single gene Ms11 controlling 1970s. However, the identification of CMS by Leclercq NMS, and NMS801 and NMS373 are two inbred lines with the NMS (1969) and the subsequent discovery of fertility restora- gene Ms10. The objectives of this study were to (i) identify molecular tion genes (Kinman, 1970; Leclercq, 1971; Vranceanu and markers linked with the Ms10 and the Ms11 NMS genes, and (ii) place Stoenescu, 1971) introduced a CMS system and quickly these genes on the genetic map of sunflower. Three F2 and a BC1F1 replaced the NMS system for producing hybrid seed. mappingpopulationsdevelopedfromcrossesbetweenthemale-sterile In contrast to CMS and its commercial use for hybrid (MS) lines P21, NMS801, and NMS373, and male-fertile (MF) (wild- production, NMS can improve efficiency of hybridiza- type)lineswerescoredforfertility/sterility.TheNMS801andNMS373 tion by eliminating tedious hand emasculation, enhance populations segregated for Ms10 and T, a tightly linked anthocyanin pigment locus. The P21 populations segregated for Ms11. These popula- random mating for population development and recur- tions were then genotyped with restriction fragment length polymor- rent selection, and facilitate the development of testers phism (RFLP), simple sequence repeat or microsatellite (SSR), and for inbred line evaluation and selection (Jan, 1992). Nu- insertion-deletion polymorphism (INDEL) markers, and four genetic clear male sterility is usually controlled by single reces- maps comprising 14 to 17 linkage groups (LGs) were constructed for sive genes, although control by two complementary re- each population. The Ms10 and T genes mapped to LG 11, while the cessive genes and two genes with epistatic effects have Ms11 gene mapped to LG 8. Four SSR markers (ORS697, ORS1214, also been described (Miller and Fick, 1997). Allelic rela- ORS686, and CRT162) and the phenotypic marker locus T cosegre- tionships among NMS genes have been reported.Vran- gated and were tightly linked to Ms10 at a genetic distance of less than ceanu (1970) tested for allelism among 10 NMS sources 1 cM. The Ms11 gene locus was flanked by the SSR markers MS925 isolated from Romanian germplasm and reported the and ORS536 at genetic distances of 3.8 and 4.1 cM, respectively. The availability of tightly linked polymerase chain reaction based markers presence of five independent NMS genes, designated Ms1 and the location of NMS genes on the sunflower genetic map will be to Ms5. Jan (1992) evaluated seven induced NMS mu- useful for marker-assisted selection (MAS) in sunflower breeding tants and two NMS lines, P21 and B11A3, for allelic re- programs and provides a basis for the physical mapping and positional lationships and demonstrated the existence of six inde-
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A backcrossing programme was carried out both to assess the stability of a cytoplasmic male-sterility (CMS) source from Helianthus resinosus, designated RES1, and to incorporate it into inbred sunflower lines (HA89, RHA271, RHA801). All the progenies, grown in different environments, were completely male-sterile. This suggests that the expression of this cytoplasm is stable. Female-fertility of lines HA89, RHA271 and RHA801 carrying CMS RES1 were compared with those of the corresponding fertile inbred lines. There were no differences in the number of seeds per head. This indicates that female-fertility is not affected by RES1 cytoplasm. Cytological studies showed that meiosis proceeds normally until the tetrad stage; consequently, the absence of pollen is caused by alterations that take place during postmeiotic stages. With the aim of identifying male-fertility restorer genotypes, crosses were made between HA89 (CMS RES1) plants and different annual diploid and perennial hexaploid Helianthus species. All the diploid germplasm evaluated behaved as a CMS RES1 maintainer. However, the hexaploid species, H. resinosus, H. x laetiflorus, H. pauciflorus and H. tuberosus, restored pollen fertility in CMS RES1 plants.
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A new cms source, ANN-5, was found in wild Helianthus annuus. This source showed high stability under different conditions in 1991 and 1992. All progenies from crosses of this source with several stable B-lines and restorer lines, which are homozygous for the gene which restores Leclercq's source of male sterility, were completely male sterile. Flower contained pistils and atrophied stamens. The cytological analysis showed that pollen mother cell degeneration took place in a premeiotic stage.
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Helianthus petiolaris (Asteraceae) native to North America has naturalized in Argentina. The extensive overlapping with sunflower crop regions, the coincidence of life cycles and the common pollinators facilitate interspecific crosses with sunflower, H. annuus var. macrocarpus. To estimate the occurrence of crop-to-wild and wild-to-crop gene flow, off-type plants in progenies of pure stands of both species flowering in coincidence and the presence of crop alleles in H. petiolaris populations were investigated in 26 wild populations and nine crop fields. Morphological traits and RAPD markers were used to attempt hybrid characterization. Off-type individuals were found in frequencies of 0.5 and 0.3% among crop progenies and wild populations, respectively. Off-type plants showed intermediate values for metric morphological traits and low fertility traits. Some off-type plants proved to carry crop alleles based on molecular analysis. The average frequency of cultivar-marker introgression across the wild populations was very low (0.02). Although observed hybridization rates seem to be low, the extension of crop-wild overlapping in Argentina make hybrid formation a noticeable process. Therefore, the new sunflower varieties and eventually GM varieties would transfer their traits through pollen flow and they would persist in H. petiolaris populations. KeywordsCrop-wild hybridization-Introgression-Morphological traits-RADP markers
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Cytoplasmic male-sterile lines CMS89 and CMSBaso of sunflower (Helianthus annuus) differ from the fertile lines HA89 and Baso in a mitochondrial DNA sequence in the vicinity of theatpA gene. In addition, the transcriptional pattern of theatpA gene is changed in male-sterile lines compared to fertile ones. Besides one main transcript in the fertile lines, the male-sterile lines additionally show larger transcripts. Investigation of Baso and CMSBaso revealed that the two fertility-restored lines of CMS89 have the same transcripts as CMSBaso or a combination of CMSBaso and CMS89. Comparing the mitochondrialin organello translation products we observed a unique 16 kDa protein, which is expressed in male-sterile lines carrying theH. petiolaris cytoplasm but is not detectable in fertile lines withH. annuus cytoplasm. The 16 kDa protein can also be observed in restored lines but not inH. petiolaris. As the expression of the 16 kDa polypeptide seems to be linked to the interspecific cross betweenH. petiolaris andH. annuus it may play a role in CMS. By different criteria such as molecular mass, isoelectric point and peptide fingerprinting the subunit of the F1-ATPase of male-sterile and fertile lines is very similar if not identical.
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The localization of two wild annual Helianthus species recently established in Argentina, H. annuus and H. petiolaris, were found to be connected with climate, soil, and agroecosystem variables. The habitats of both species, being mainly roadsides, were strongly related to disturbance, but they were also found in riparian areas and within crops. Microhabitat conditions allowed clear differentiation among the species’ preferences, H. petiolaris appeared associated with sandy soils with low organic matter content, while H. annuus showed preference for more fertile and fine textured soils. In the western region of the country, irrigation strongly modified the environment favoring H. annuus. No variables allowed characterization of the three sites, where both species grew together.
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Wild sunflower Helianthus annuus originates from North America and has naturalised in Argentina where it is considered invasive. The present study attempts to assess the genetic diversity using two different molecular marker systems to study the wild genetic patterns and to provide data applicable to conservation and breeding uses. Ten natural populations sampled throughout the wild range and six inbred lines were studied using inter-simple sequence repeat (ISSR) and simple sequence repeats (SSR) markers. A total of 64 ISSR bands and 29 SSR alleles were produced from 106 wild and cultivated plants. We found 9 ISSR private bands and 21 SSR private alleles in wild accessions, but no private bands/alleles were found in cultivated sunflowers. Molecular variability in wild populations was approximately 60% higher than in inbred lines. Local wild sunflowers kept considerable diversity levels in comparison with populations in the centre of origin (approximately 70%) and therefore they might possess a potential for adaptive evolutionary change. Analysis of molecular variance (AMOVA) indicated population structure with nearly 20% of genetic variability attributable to between-population differentiation. Principal coordinate analyses (PCO) grouped wild populations from different geographic locations, and a Mantel test showed low congruence between genetic distance (GD) and geographic distances (GGD); hence, molecular data could not rule out multiple wild introduction events. Low correlations were found between ISSR and SSR GD at individual and population levels; thus, divergent evolutionary groups were not evident in local wild sunflowers. Several genetic diversity criteria were utilised to assign conservation value and certain wild populations emerged as interesting sites for more extensive sampling.