Molecular Evidence and the Origin and Development of the Domesticated Sunflower (Helianthus annum, Asteraceae)

The domesticated sunflower,Helianthus annuus, is an important economic crop, yet molecular data regarding its evolution are limited. Here we review morphological, geographical, archaeological, and molecular evidence pertaining to its origin and development. New isozyme and chloroplast DNA (cpDNA) evidence is also presented. Morphological, geographical, and archaeological evidence has led to the hypothesis that the domesticated sunflower was derived from a wild/weedy form ofH. annuus possibly in the Midwest. Molecular evidence was concordant with this hypothesis. A high degree of enzymatic and cpDNA sequence similarity was observed between wild and domesticatedH. annuus, and domesticatedH. annuus contained a subset of the alleles and cpDNAs found in wildH. annuus. The extensive polymorphism in the wild plants and the virtual monomorphism in cultivated lines for both isozyme and cpDNA phenotypes further suggest a single origin of the domesticated sunflower from a very limited gene pool. In addition, Native American varieties of the domesticated sunflower were genetically more variable than other cultivated lines, possibly indicating that they gave rise to the other cultivated stocks. Molecular evidence did not, however, allow conclusions as to the exact geographic origin of the domesticated sunflower.     

Photosynthesis,dry matter accumulation and distribution in the wild sunflower Helianthus petiolaris and the cultivated sunflower Helianthus annuus as influenced by water deficits

Summary This study reports on the effects of water deficits on photosynthesis, plant growth and carbon allocation in the wild sunflower Helianthus petiolaris and in the cultivated sunflower Helianthus annuus grown under controlled conditions in the glasshouse. Water deficits reduced the rate of net photosynthesis and the dry weight of leaves, stems, roots and reproductive parts in both species. The root-to-shoot ratio of about 0.05 in H. petiolaris was lower than the root-to-shoot ratio of about 0.15 in H. annuus. Water stress did not affect the root-to-shoot ratio, but increased the percentage of roots at depth in H. annuus. The decrease in growth induced by water deficits was a consequence of a reduction in both leaf area production and net photosynthesis. Flowering occurred earlier in H. petiolaris than in H. annuus with a consequent earlier allocation of carbon to reproductive parts in the wild compared to the cultivated sunflower. The time to budding and flowering of either species was not altered by mild water stress, but was delayed by severe water deficits. During mild water stress carbon allocation to stems decreased, but that to reproductive parts increased. When plants were severely stressed and then rewatered the proportion af carbon allocated to leaves increased and the proportion allocated to stems decreased when compared to unstressed plants. The adaptative role of these features is discussed.     

Molecular Evidence and the Origin and Development of the Domesticated Sunflower (<Emphasis Type="Italic">Helianthus annum</Emphasis>, Asteraceae)

The domesticated sunflower,Helianthus annuus, is an important economic crop, yet molecular data regarding its evolution are limited. Here we review morphological, geographical, archaeological, and molecular evidence pertaining to its origin and development. New isozyme and chloroplast DNA (cpDNA) evidence is also presented.Morphological, geographical, and archaeological evidence has led to the hypothesis that the domesticated sunflower was derived from a wild/weedy form ofH. annuus possibly in the Midwest. Molecular evidence was concordant with this hypothesis. A high degree of enzymatic and cpDNA sequence similarity was observed between wild and domesticatedH. annuus, and domesticatedH. annuus contained a subset of the alleles and cpDNAs found in wildH. annuus. The extensive polymorphism in the wild plants and the virtual monomorphism in cultivated lines for both isozyme and cpDNA phenotypes further suggest a single origin of the domesticated sunflower from a very limited gene pool. In addition, Native American varieties of the domesticated sunflower were genetically more variable than other cultivated lines, possibly indicating that they gave rise to the other cultivated stocks. Molecular evidence did not, however, allow conclusions as to the exact geographic origin of the domesticated sunflower.     

Morphometric Analysis of Sunflower (<Emphasis Type="Italic">Helianthus annuus</Emphasis> L.) Achenes from Mexico and Eastern North America<Superscript>1</Superscript>

Morphometric Analysis of Sunflower ( Helianthus annuus L.) Achenes from Mexico and Eastern North America. Sunflower (Helianthus annuus L.) has played a major role in the evolution of agricultural systems in the Americas. The discovery of ancient domesticated remains from archaeological deposits in pre-Columbian Mexico offers new dimensions to widely accepted viewpoints on the domestication pattern of H. annuus. Although American sunflower populations north of Mexico have been examined extensively, Mexican indigenous domesticated landraces have not been studied in any detail. In this study, we morphologically assessed wild and domesticated sunflower achenes from Mexico and compared them to similar datasets from eastern North America. Additionally, we evaluated the utility of four computer-assisted shape measurements in discriminating between wild and domesticated sunflower achenes (fruits) and compared variation in achene size among modern wild and cultivated populations from both Mexico and the U.S. We found that, of the shape parameters tested, none were informative in distinguishing wild achenes from domesticated varieties. Subsequent size analysis, using conventional parameters of length, width, and thickness, showed that modern wild populations from Mexico had smaller achenes compared to modern populations from eastern North America. Domesticated achenes unearthed from Mexican archaeological sites, however, were significantly larger than the early domesticated specimens recovered from eastern North America. Our methodological results indicate that variation in archaeological sunflower achenes is better described by conventional size parameters rather than computerized shape analysis.     

Cytogenetic analysis of interspecific hybrid Helianthus praecox × H. annuus, its parental forms, and two backcrosses

Meiosis of wild (Helianthus praecox) and cultivated (H. annuus) sunflower species, their F₁ interspecific hybrid, and two backcross generations were studied. A low level of meiotic chromosomal aberrations in the parents was detected. Interspecific hybridization between wild and cultivated sunflower accessions led to a considerable (50%) increase in the rate of meiotic aberrations in microsporocytes. Backcrossing of hybrids to cultivated sunflower decreased the chromosomal aberration rate to 12.8% in BC₁ and to 9.6% in BC₂. Cytological stability of plants was restored only in BC₂.     

Genome scan of hybridizing sunflowers from Texas (Helianthus annuus and H. debilis) reveals asymmetric patterns of introgression and small islands of genomic differentiation

Although the sexual transfer of genetic material between species (i.e. introgression) has been documented in many groups of plants and animals, genome‐wide patterns of introgression are poorly understood. Is most of the genome permeable to interspecific gene flow, or is introgression typically restricted to a handful of genomic regions? Here, we assess the genomic extent and direction of introgression between three sunflowers from the south‐central USA: the common sunflower, Helianthus annuus ssp. annuus; a near‐endemic to Texas, Helianthus debilis ssp. cucumerifolius; and their putative hybrid derivative, thought to have recently colonized Texas, H. annuus ssp. texanus. Analyses of variation at 88 genetically mapped microsatellite loci revealed that long‐term migration rates were high, genome‐wide and asymmetric, with higher migration rates from H. annuus texanus into the two parental taxa than vice versa. These results imply a longer history of intermittent contact between H. debilis and H. annuus than previously believed, and that H. annuus texanus may serve as a bridge for the transfer of alleles between its parental taxa. They also contradict recent theory suggesting that introgression should predominantly be in the direction of the colonizing species. As in previous studies of hybridizing sunflower species, regions of genetic differentiation appear small, whether estimated in terms of F_ST or unidirectional migration rates. Estimates of recent immigration and admixture were inconsistent, depending on the type of analysis. At the individual locus level, one marker showed striking asymmetry in migration rates, a pattern consistent with tight linkage to a Bateson–Dobzhansky–Muller incompatibility.     

Increased pre-dispersal seed predation in sunflower crop-wild hybrids

The fitness of crop-wild hybrids can influence gene flow between crop and wild populations. Seed predation levels in crop-wild hybrid plants can be an important factor in determining plant fitness, especially in large-seeded crops such as sunflower. To determine patterns of pre-dispersal seed predation, seeds were collected from wild sunflowers (Helianthus annuus L.) and wild×crop F₁ hybrids at three experimental field sites in eastern Kansas. Seed heads were dissected and each seed was counted and scored for categories of seed damage by lepidopteran and coleopteran larvae. Hybrid seed heads showed significantly higher levels of insect-damaged seeds. The average hybrid plant had 36.5% of its seeds (or 45.1 seeds per plant) eaten by insect larvae while the average wild plant lost only 1.8% (or 95 seeds) to seed predators. Hybrid populations had higher levels of total insect damage even when date of flowering, flower head diameter, and the number of open heads within the study site were accounted for. These results suggest that the reduced fecundity of F₁ crop-wild sunflower hybrids demonstrated in other studies may be augmented by the increased seed predation in hybrid flower heads. Fecundity estimates of crop-wild hybrid and wild plants that disregard differential seed predation levels may not accurately reflect the actual relative contributions of hybrid and wild plants to future generations. Received: 21 December 1998 / Accepted: 8 July 1999     

Reevaluation of biosecurity of Ophraella communa against sunflower (Helianthus annuus)

Ophraella communa (Coleoptera: Chrysomelidae), originally from North America, has been used for biological control of common ragweed, Ambrosia artemisiifolia, in China since 2007. However, there is still a debate on whether O. communa can attack sunflowers under field conditions. To re-evaluate the biosecurity of O. communa against sunflower (Helianthus annuus), we investigated the population density of O. communa on three sunflower varieties that were intercropped with or planted in circumambience of A. artemisiifolia under field conditions. Our results showed that only very few O. communa eggs (<0.5 eggs/plant) were found on sunflower plants at the last two surveys when sunflowers were planted in circumambience of common ragweed. O. communa eggs were not found on sunflower plants at each survey when sunflowers were intercropped with common ragweed. The first–second instar larvae, third instar larvae, pupae and adults of O. communa were occasionally found on sunflower plants, but their densities were very low under either case of planting patterns. Based on these results, we conclude that sunflower is not a potential host plant for O. communa and the beetle is an effective host-specific biological control agent of common ragweed.     

Mechanisms of resistance to the brown planthopperNilaparvata lugens in wild rice (Oryza spp.) cultivars

Three wild rice species and six cultivated rice varieties were evaluated to determine their mechanisms of resistance toNilaparvata lugens (Stal.). Wild rice species,Oryza officinalis, O. punctata, andO. latifolia and cultivated rices Rathu Heenati (Bph 3), Babawee (bph 4), ARC 10 550 (bph 5), Swarnalata (Bph 6), Ptb 33 (bph 2+Bph 3) and the susceptible Taichung Native (TN 1) (no resistance gene) were included in the study. In a free choice seedbox screening test, wild rice species maintained their high level of resistance through the 48 h exposure toN. lugens nymphs while plant damage ratings of cultivated rice varieties increased with time. Wild rices were non preferred and significantly more individuals settled on susceptible TN 1 followed by cultivated rices. The quantity of food ingested and assimilated byN. lugens on wild rices was less than on cultivated resistant varieties.N. lugens caged on resistant wild rices had slow nymphal development, reduced longevity, low fecundity, and low egg hatchability as compared toN. lugens on cultivated resistant varieties.     

Leaf expansion as related to plant water availability in a wild and a cultivated sunflower

This study aimed to determine if two species of sunflower, Helianthus annus L. cv. Hysun 31 (cultivated, single-stemmed genotype) and Helianthus petiolaris Nuttall ssp. fallax (wild, many-hranched genotype) differed in the response of leaf growth to water deficits. Earlier published studies, concerned only with H. annuus, failed to reveal differences in the response of sunflowers to water stress. Plants of the two species were paired in large containers of soil and grown under high radiation in a glasshouse. One batch of plants was irrigated and the other allowed to dry so that predawn leaf water potentials declined at an average of 0.072 MPa day^?1. The dry batch was rewatered when predawn leaf water potentials reached ?0.85 MPa. The stress imposed was sufficient to curtail leaf growth so that plants in the dry treatment had only 60% of the leaf area of irrigated plants at the onset of rewatering. Both species were affected by stress to the same relative extent, though their leaf areas at this stage differed 7-fold. Both genotypes also recovered to the same degree in the long term, finally having leaf areas and gross dry matter distribution patterns which were indistinguishable from plants which were irrigated throughout. However, water stress resulted in different distribution patterns of leaf area: H. annuus produced larger leaves at the top of its single stem which compensated for the reduced area in lower leaves, whereas H. petiolaris compensated in the leaves on its branches. Leaves which emerged after the time of stress were most able to compensate in area subsequently. For example, those leaves of H. annuus which emerged one week after stress-relief were more than three times larger than comparable leaves on plants irrigated continuously. Leaf expansion rates were affected earlier in the stress cycle than leaf conductance in H. annuus, but not in H. petiolaris. But as with other plant responses to water stress, the differences between the two species were small.     

Allozyme variation in domesticated annual sunflower and its wild relatives

 The annual sunflower (Helianthus annuus L.) is a morphologically and genetically variable species composed of wild, weedy, and domesticated forms that are used for ornament, oilseed, and edible seeds. In this study, we evaluated genetic variation in 146 germplasm accessions of wild and domesticated sunflowers using allozyme analysis. Results from this survey showed that wild sunflower exhibits geographically structured genetic variation, as samples from the Great Plains region of the central United States were genetically divergent from accessions from California and the southwestern United States. Sunflower populations from the Great Plains harbored greater allelic diversity than did wild sunflower from the western United States. Comparison of genetic variability in wild and domesticated sunflower by principal coordinate analysis showed these groups to be genetically divergent, in large part due to differences in the frequency of common alleles. Neighbor-Joining analyses of domesticated H. annuus, wild H. annuus and two closely related wild species (H. argophyllus T. & G. and H. petiolaris Nutt.) showed that domesticated sunflowers form a genetically coherent group and that wild sunflowers from the Great Plains may include the most likely progenitor of domesticated sunflowers. Received: 2 December 1996/Accepted: 4 April 1997     

Regeneration of fertile interspecific hybrids from protoplast fusions between Helianthus annuus L. and wild Helianthus species

The use of interesting characteristics from wild Helianthus species in sunflower breeding is limited by poor crossability or sterility of interspecific hybrids. To overcome this barrier, mesophyll protoplasts of Sclerotinia sclerotiorum-resistant clones of Helianthus maximiliani, H. giganteus and H. nuttallii were fused with hypocotyl protoplasts of H. annuus in the presence of polyethyleneglycol and dimethylsulfoxide. Fusion products were embedded in agarose and subjected to a regeneration protocol developed for sunflower protoplasts. Organogenic calli were transferred onto solid medium and emerging shoots were elongated in the absence of plant growth regulators. Rooting of shoots was induced by a 1-naphthaleneacetic acid treatment and putative hybrid plants from fusions between H. annuus + H. maximiliani and H. annuus + H. giganteus were transferred into the greenhouse. All of them exhibited a hybrid phenotype with a high percentage of rhizome producing plants. Their hybrid origin was confirmed by random amplified polymorphic DNA analysis. Plants flowered after 3–4 months and set seeds, of which 70–80% germinated. Received: 18 February 1997 / Revision received: 25 March 1997 / Accepted: 15 May 1997     

Female preference and larval performance of sunflower moth,Homoeosoma electellum,on sunflower pre‐breeding lines

The preference–performance hypothesis for insect herbivores predicts that adult females should preferentially choose hosts on which their offspring perform better. We tested this hypothesis for the sunflower moth, Homoeosoma electellum (Hulst) (Lepidoptera: Pyralidae), using 16 sunflower (pre‐breeding) lines, derived from a number of wild species of Helianthus, including Helianthus annuus L., Helianthus deserticola Heiser, Helianthus paradoxus Heiser, Helianthus praecox Engelm. & Gray ssp. hirtus (Heiser) Heiser, Helianthus praecox Engelm. & Gray ssp. runyonii (Heiser) Heiser, Helianthus petiolaris Nutt., Helianthus resinosus Small, and Helianthus tuberosus L. (Asteraceae), that are suitable for introducing wild sunflower germplasm into commercial cultivars. Female moths showed a range of ovipositional preference measures to the various lines. Combined data for three Helianthus species represented by multiple lines showed significant differences in female preference with respect to the parental species. Larval performance, determined by proportion of infested neonate larvae reaching the pupal stage, or mean pupal weight, varied across the lines and, as for the female preference data, also showed significant differences among the three parental Helianthus species represented by multiple lines. These data suggest that the characteristics in the pre‐breeding lines influencing female sunflower moth preference and larval performance likely originate from the parental species and may be consistently transferred to the derived pre‐breeding lines. Of particular note with regard to potential plant resistance mechanisms, lines derived from H. tuberosus showed consistent low preference–performance measures. Female preference and larval performance (for both measures) were strongly correlated, indicating that females preferred plants and lines on which larvae performed better, in support of the preference–performance hypothesis.     

Oil concentration and fatty acid composition of achenes ofHelianthus species (Asteraceae) from Canada

The cultivated sunflower (Helianthus annuus) is one of the four most important annual crops in the world grown for its edible oil. Species of the genusHelianthus served as the ancestral stock for the present cultivated sunflower. The wild relatives are a valuable genetic reservoir for improving the crop species. This study examined oil concentration and fatty acid composition in oil of two annualHelianthus species (31 populations) and four perennial species (32 populations) from the prairie provinces of Canada. The highest average oil concentration was observed in annualH. petiolaris with 31.3%. Among the perennials,H. maximiliani Schrad. had the highest average oil concentration with 31.1%.Helianthus tuberosus L. had the highest average palmitic (16:0) acid concentration with 8.0%, while the lowest value was observed inH. petiolaris with 4.0%. The highest average stearic (18:0) acid concentration was found inH. annuus with 2.9%, whileH. petiolaris had the lowest with 2.3%. The highest average oleic acid (18:1) was observed in H. petiolaris (18.4%), and the highest linoleic (18:2) was observed inH. maximiliani (77.4%). The variability within the wild species appears to be sufficient for altering oil and fatty acid characteristics in cultivated sunflower.     

Behavioral and physiological responses of rice leaffolder Cnaphalocrocis medinalis to selected wild rices

Of four wild rices evaluated, Oryza perennis and O. punctata showed resistance to rice leaffolder, Cnaphalocrocis medinalis (Guenée), whereas O. australiensis and O. nivara were moderately resistant. C. medinalis larvae showed a strong nonpreference for settling and feeding on Oryza australiensis, O. perennis and O. nivara as compared to susceptible IR36 rice variety. Among wild rices tested, however, only O. australiensis, was more preferred for larval settling and feeding than resistant TKM6 plants. The growth index of C. medinalis on all wild rices, except O. punctata was significantly lower than on IR36 and TKM6 plants. First-instar larvae caged on O. perennis showed significantly lower larval and pupal weights than those on other wild rices. Incorporation of dry leaf powder of O. punctata and O. perennis wild rices in an artificial diet caused high larval mortality. Ovipositing gravid females showed less preference for wild rices than for IR36 and TKM6 plants.Based at the International Rice Research Institute (IRRI), P.O. Box 933, Manila, Philippines     

Sublethal effects of chlorantraniliprole and thiamethoxam seed treatments when Lysiphlebus testaceipes feed on sunflower extrafloral nectar

The extrafloral nectar (EFN) of sunflower, Helianthus annuus L., is an important summer resource for many insects and represents a potential route of exposure to systemic insecticides applied as seed treatments to cultivated varieties. Among the many parasitoids that utilize sunflower EFN, Lysiphlebus testaceipes (Cresson) (Hymenoptera: Braconidae) is an important generalist parasitoid of cereal aphids in North America. This study evaluated the performance of adult wasps fed EFN of sunflower plants grown from seed treated with chlorantraniliprole and thiamethoxam. Consumption of EFN from treated sunflower seedings caused no lethal effects, but reduced the numbers of greenbug nymphs, Schizaphis graminum Rondani, attacked and parasitized when wasps foraged in Petri dish arenas. Whereas control females self-superparasitized every fourth host, those exposed to chlorantraniliprole did not. Offspring developmental time and adult emergence were unaffected by either treatment, but thiamethoxam greatly reduced the proportion of female offspring.     

The tortoise beetle Physonota maculiventris (Chrysomelidae: Cassidinae) is suitable for release against the weedy Mexican sunflower Tithonia diversifolia (Asteraceae) in South Africa

The biology and host range of the defoliating beetle Physonota maculiventris Boheman (Chrysomelidae: Cassidinae) were studied in quarantine to determine its suitability for release as a biological control agent against Mexican sunflower, Tithonia diversifolia (Hemsl.) A. Gray (Asteraceae), in South Africa. Females laid 5.25?±?0.25 (mean?±?SE) egg batches during their lifetimes, with each batch consisting of approximately 33 eggs. Larvae were highly gregarious as early instars and both larvae and adults fed voraciously, often defoliating the plants completely. The life cycle of the beetle was completed in 67.5?±?7.5 days under quarantine conditions. Among the 58 test plant species subjected to no-choice tests, P. maculiventris developed successfully on T. diversifolia and some sunflower (Helianthus annuus L.) cultivars. However, only minor damage was recorded on non-target species, notably the exotic weed Xanthium strumarium L. and some H. annuus cultivars. Also, survival to adulthood was considerably lower on sunflower cultivars than on the target weed during these tests. During choice tests, P. maculiventris oviposited and developed successfully on T. diversifolia only, with only minor feeding damage on some H. annuus cultivars, suggesting that the beetle’s field host range will be confined to the target weed. Risk analysis also showed that P. maculiventris presents an extremely low risk to non-target plant species (e.g. within the tribe Heliantheae and other close relatives). The study concluded that P. maculiventris is safe for release in South Africa and an application for its release is being considered by the relevant South African regulatory authorities.     

Genetic relationships among domesticated and wild sunflowers (Helianthus annuus,Asteraceae)

Randomly amplified polymorphic DNA (RAPD) loci were used to investigate the origin and genetic relationships of the domesticated sunflower and its wild relatives. A total of 13 primers was employed for the PCR amplifications, from which 68 polymorphic loci were scored. Analysis of RAPD data supports the origin of the domesticated sunflower from wildH. annuus. The high RAPD identity between wild and domesticatedH. annuus (I = 0.976 to I = 0.997) is concordant with a progenitorderivative relationship. However, the identities are very high and therefore provide little information regarding the geographic origin of the domesticated sunflower. Nonetheless, some inferences concerning relationships among domesticated sunflower accessions can be made. The native American varieties and old landracesform a genetically cohesive group based on RAPD evidence, probably due to their origin prior to the use of interspecific hybridization in the development of sunflower cultivars. In contrast, the modern cultivars are not genetically cohesive, perhaps due to the extensive use of intraspecific and interspecific hybridization in the development of modern sunflower varieties. Likewise, little concordance was observed between the geographical origin and genetic clustering of wild populations—an observation probably best explained by the weedy, human dispersed nature of wildH. annuus populations. The information presented here may be a reliable indicator of genetic relationships among wild and domesticated sunflower accessions. However, the processes generating the observed relationships are complex, and the occurrence of unexpected groupings or absence of predicted ones will probably remain difficult to understand.     

Intra-individual heterogeneity of rDNA allows the distinction between two closely related species in the Genus Helianthus

The Ribosomal DNAs of Helianthus annuus and H. argophyllus were analysed. Total DNA from single individuals of six cultivated lines, one wild ecotype ofH. annuus, and three ecotypes of H. argophyllus, were digested with various restriction enzymes. Hybridisation of Southern blots with sunflower ribosomal probes containing most of the interspacer regions (R3) or the 25 s coding region (R2) reveals different patterns from those expected: while no difference between H. annuus and H. argophyllus had been observed in previous rDNA RFLP analysis, our study clearly distinguished the two species on the basis of two different patterns when using R3 and BamHI, BstYI, or EcoRI/BamHI. Furthermore, the sum of the fragment weights of the BamHI restriction patterns was much greater than that of the rDNA entire unit-weight space. The co-existence of different rDNA units within single individuals is proposed as a model to explain these results. Four rDNA units were distinguished, which differed in their state of methylation and by the presence of mutations at two BamRI restriction sites. H. annuus individuals displayed two types of rDNA units while H. argophyllus individuals displayed four types.     

The persistence of cultivar alleles in wild populations of sunflowers five generations after hybridization

 The development of transgenic plants has heightened concern about the possible escape of genetically engineered material into the wild. Hybridization between crops and their wild relatives provides a mechanism by which this could occur. While hybridization has been documented between several crops and wild or weedy relatives, little is known about the persistence of cultivar genes in wild populations in the generations following hybridization. Wild and weedy sunflowers occur sympatrically with cultivated sunflowers throughout much of the cultivation range, and hybridization is known to occur. We surveyed two cultivar-specific RAPD markers in 2700 progeny in a naturally occurring population of wild Helianthus annuus over five generations following a single generation of hybridization with the cultivar. Moderate levels of gene flow were detected in the first generation (42% hybrids at the crop margin) and cultivar allele frequencies did not significantly decline over four subsequent generations. These results indicate that gene flow from cultivated into wild populations of sunflowers can result in the long-term establishment of cultivar alleles in wild populations. Furthermore, we conclude that neutral or favorable transgenes have the potential to escape and persist in wild sunflower populations. Received: 1 November 1996/Accepted: 17 January 1997