Gerald J. Seiler

Long-term introgression of crop genes into wild sunflower populations

Abstract A strategy of DNA pooling aimed at identifying markers linked to quantitative trait loci (QTLs), ‘Sequential Bulked Typing’ (SBT), is presented. The method proposed consists in pooling DNA from consecutive pairs of individuals ranked phenotypically, i.e., pools are formed with individuals ranked (1st, 2nd), (3rd, 4th),…, (N-1st, Nth). The N/2 pools are subsequently amplified using the polymerase chain reaction (PCR). If the whole population is typed the number of PCRs per marker is halved with respect to individual typing (IT). But if this strategy is combined with selective genotyping of extreme individuals savings can be further increased. Two extreme cases are considered: in the first one (SBT0), it is assumed that only presence or absence of a given allele can be ascertained in a pool; in the second one (SBT1), it is further assumed that differences between allele band intensities can be distinguished. The theory to estimate by maximum likelihood the QTL effect and its position with respect to flanking markers is presented. The behaviour of IT and SBT was studied using stochastic computer simulation in backcross and F2 populations. Three percentages of subpattern distinction (0, 50 and 100%) two population sizes (n=1200 and 600) and two QTL effects (a=0.1 and 0.25 standard deviations) were considered. SBT1 had the same power as individual genotyping at half the genotyping costs in all situations studied. Accuracy of QTL location is not increased with a dense number of markers, as opposed to individual typing. As a result DNA pooling is not useful for accurate location of the QTL but rather to pick up genome regions containing QTLs of at least moderate effect. The theory developed provides the general theoretical framework to deal with any DNA pooling strategy aimed at detecting QTLs.

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.

Introgression between the Cultivated Sunflower and a Sympatric Wild Relative, Helianthus petiolaris (Asteraceae)

High rates of hybridization and introgression have been reported between the cultivated sunflower and its wild progenitor (both Helianthus annuus), raising concerns that neutral or favorable transgenes might escape and persist in wild H. annuus populations. However, little consideration has been given to the possibility that other wild sunflower species may hybridize with the cultivated sunflower. Here, we estimate the frequency of hybridization and introgression between the cultivated sunflower and Helianthus petiolaris, a closely related wild species whose range almost completely overlaps that of the cultivated sunflower in the central and northern plains and which hybridizes extensively with wild H. annuus. Assays of 21 cultivar‐specific AFLP (amplified fragment length polymorphism) markers in 159 individuals from four sympatric populations of H. petiolaris revealed low rates of introgression, with average marker frequencies per population ranging from 0.006 to 0.026. Twenty‐seven individuals had a hybrid ancestry, and all hybrids appeared to represent later‐generation backcrosses. There was significant heterogeneity in rates of introgression for different markers, and eight of the 21 markers failed to introgress into any of the four populations. This and other evidence indicate that the H. petiolaris genome may be differentially permeable to introgression. These data indicate that (1) beneficial and neutral transgenes will take much longer to move into H. petiolaris populations than into wild H. annuus; (2) the risk of escape may depend on the genomic location of the transgene; and (3) escape is likely to be sporadic, occurring in some populations and not others and at different times. Thus, risk assessment in wild H. annuus is of more immediate concern than in H. petiolaris.

Sunflower genetic, genomic and ecological resources

Long a major focus of genetic research and breeding, sunflowers (Helianthus) are emerging as an increasingly important experimental system for ecological and evolutionary studies. Here, we review the various attributes of wild and domesticated sunflowers that make them valuable for ecological experimentation and describe the numerous publicly available resources that have enabled rapid advances in ecological and evolutionary genetics. Resources include seed collections available from germplasm centres at the USDA and INRA, genomic and EST sequences, mapping populations, genetic markers, genetic and physical maps and other forward‐ and reverse‐genetic tools. We also discuss some of the key evolutionary, genetic and ecological questions being addressed in sunflowers, as well as gaps in our knowledge and promising areas for future research.

Fitness effects and genetic architecture of plant–herbivore interactions in sunflower crop–wild hybrids

*Introgression of cultivar alleles into wild plant populations via crop-wild hybridization is primarily governed by their fitness effects as well as those of linked loci. The fitness of crop-wild hybrids is often dependent on environmental factors, but less is understood about how aspects of the environment affect individual cultivar alleles. *This study investigated the effects of naturally occurring herbivory on patterns of phenotypic selection and the genetic architecture of plant-herbivore interactions in an experimental sunflower crop-wild hybrid population in two locales. *Phenotypic selection analyses suggested that cultivar alleles conferring increased size were generally favored, but at one site cultivar-like flowering time was favored only if three types of herbivory were included in the selection model. Quantitative trait locus (QTL) mapping identified three regions in which the cultivar allele conferred a selective advantage for a number of co-localized traits. Quantitative trait loci for several measures of insect herbivory were detected and, although the cultivar allele increased herbivory damage at the majority of these QTLs, they rarely colocalized with advantageous cultivar alleles for morphological traits. *These results suggest that a subset of cultivar traits/alleles are advantageous in natural environments but that herbivory may mitigate the selective advantage of some cultivar alleles.

Influence of temperature on primary and lateral root growth of sunflower seedlings

Abstract Roots play a major role in maintaining the supply of water and nutrients to plant tissues. There are numerous environmental factors such as temperature that can influence the growth and function of root systems. While we have some information about rooting depth in sunflower, we lack information about early root growth and its response to temperature in diverse genotypes based on wild sunflower species. The wild progenitors of the crop species are potential sources for enhancing the rooting system of cultivated sunflower. Root growth characteristics of seedlings of six genetically diverse sunflower ( Helianthus ) genotypes and two cultivated hybrids were evaluated during a 10-day period to determine early chronological root growth as influenced by temperature. Root growth was evaluated at temperatures of 10–40°C in 5°C increments. Primary root length, lateral root length, number of lateral roots, root fresh weight, and hypocotyl length and fresh weight were determined beginning at 3 days after planting (DAP), 7 DAP, and 10 DAP. An analysis of variance indicated that genotypes, temperatures, and days were significant sources of variation for primary and lateral root lengths, number of lateral roots, root branching density, root fresh weight, and hypocotyl length and fresh weight. Averaged over all genotypes, primary and lateral root growth was greatest in the 25–30°C temperature range at 10 DAP. Generally, very little root growth occurs at 10, 15 or 40°C. Semi-dwarf hybrid 471D had the greatest primary and lateral root growth at 30°C with 154 cm, as well as the highest number of lateral roots with 48 roots per plant. Interspecific genotypes had similar total root growth compared to cultivated hybrid 894 at 30°C. Temperature-dependent root growth information will be useful in crop modeling of sunflower. There appears to be a temperature-specific response in laboratory evaluated sunflower genotypes, but further studies are needed to correlate the studies with rooting responses under field conditions.

Identification of resistance to new virulent races of rust in sunflowers and validation of DNA markers in the gene pool.

Sunflower rust, caused by Puccinia helianthi, is a prevalent disease in many countries throughout the world. The U.S. Department of Agriculture (USDA)-Agricultural Research Service, Sunflower Research Unit has released rust resistant breeding materials for several decades. However, constantly coevolving rust populations have formed new virulent races to which current hybrids have little resistance. The objectives of this study were to identify resistance to race 336, the predominant race in North America, and to race 777, the most virulent race currently known, and to validate molecular markers known to be linked to rust resistance genes in the sunflower gene pool. A total of 104 entries, including 66 released USDA inbred lines, 14 USDA interspecific germplasm lines, and 24 foreign germplasms, all developed specifically for rust resistance, were tested for their reaction to races 336 and 777. Only 13 of the 104 entries tested were resistant to both races, whereas another six were resistant only to race 336. The interspecific germplasm line, Rf ANN-1742, was resistant to both races and was identified as a new rust resistance source. A selection of 24 lines including 19 lines resistant to races 777 and/or 336 was screened with DNA markers linked to rust resistance genes R(1), R(2), R(4u), and R(5). The results indicated that the existing resistant lines are diverse in rust resistance genes. Durable genetic resistance through gene pyramiding will be effective for the control of rust.

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.ResumenEl girasol cultivado (Helianthus annuus) es uno de las cuatro mñs importantes cosechas anuales en el mundo crecido para su aceite comestible. Especies delHelianthus sirvió como el surtido de los antepasados para girasol cultivado. Los parientes salvajes son un precioso récursos geneticó para mejorar la especies de cosecha. Este estudio examino la concentración de aceite y la compositión del ácido graso fueron determinados de dos especies deHelianthus anuales (31 poblaciones) y quatro especies perennes (32 poblaciones) procedentes de provincias de llanura de Canadá. El promedio mayor de concentración de aceite se observó en la anualH. petiolaris con 31.3%. Entre las especies perennes, laH. maximiliani tuvo el promedio mayor de concentración de aceite con 31.1%.Helianthus tuberosus tuvo el promedio mayor de concentratión de âcidos grasos, palmético (16:0) con 8.0%, mientras los valores más bajos fueron observados en la H. petiolaris con 4.0%. El promedio mayor de concentratión de esteârico (18:0) ácidos fueron observados in anuales laH. annuus con 2.9%, mientrosH. petiolaris las valores más bajos con 2.3%. El promedio mayor âcido oléico (18:1) se observó en laH. petiolaris (18.4%) y el mayor ácido linoléico (18:2) se observó en laH. maximiliani (77.4%). La variabilidad con en las especies silvestres parece haber suficiente para selectión y alteratión de las caracterésticas de aceite y ácido graso del girasol cultivado.

Ecological characterization of wild Helianthus annuus and Helianthus petiolaris germplasm in Argentina.

Fil: Poverene, Maria Monica. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Bahia Blanca. Centro de Recursos Naturales Renovables de la Zona Semiarida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiarida; Argentina

Genetic Variability for Mineral Concentration in the Forage of Jerusalem Artichoke Cultivars

SummaryOne of the potential uses of Jerusalem artichoke (Helianthus tuberosus L.) is as a forage crop. Information on inherent differences in forage nutritional quality is essential if the quality of the forage is to be improved through breeding. The objectives of this study were to determine the genotypic variability among and within forage of Jerusalem artichoke cultivars for the concentration of N, P, Ca, Mg, K and the Ca/P ratio at flowering, to determine if selection among and within cultivars is feasible, to estimate the magnitude of the genotype × environment interaction, and to examine the relationships among mineral concentrations in the forage. Ten cultivated Jerusalem artichoke cultivars grown in an irrigated field nursery at Bushland, TX were evaluated for N, P, Ca, Mg, K, and the Ca/P ratio in the forage at flowering over a 2-yr period. Cultivars, cultivar × year, and error variances were estimated to calculate the phenotypic variance. Estimates of the within-population variances were also determined. The adequacy of Jerusalem artichoke forage at flowering for maintenance of a ruminant animal was classified as follows: N, Ca, Mg, K as adequate, P inadequate, and the Ca/P ratio as excessive. There were genotypic differences among the ten cultivars for N, P, Ca, Mg, K, and the Ca/P ratio for both years and averaged across years. The magnitude of the genotypic variance components indicated that a substantial proportion of the total variation for these elements was due to cultivar, indicating the possibility of improving these elements. However, further studies on heritability and response to selection will be required before conclusions can be reached concerning the likelihood of successfully breeding for these traits.