Crop-to-wild hybridization has the potential to introduce beneficial traits into wild populations. Gene flow from genetically engineered crops, in particular, can transfer genes coding for traits such as resistance to herbicides, insect herbivores, disease, and environmental stress into wild plants. Cultivated sunflower (Helianthus annuus) hybridizes spontaneously with wild/weedy populations (also H. annuus), but little is known about the relative fitness of F1 hybrids. In order to assess the ease with which crop-to-wild introgression can proceed, we compared characteristics of F1 wild-crop progeny with those of purely wild genotypes. Two nontransgenic, cultivated varieties were crossed with wild plants from three different regions-Texas, Kansas, and North Dakota. Seed burial experiments in the region of origin showed that wild-crop seeds had somewhat higher germination rates (less dormancy) than wild seeds from Kansas and North Dakota, while no differences were seen in seeds from Texas. Progeny from each type of cross were grown in outdoor pots in Ohio and in a weedy field in Kansas to quantify lifetime fecundity and flowering phenology. Flowering periods of hybrid and wild progeny overlapped considerably, especially in plants from North Dakota and Texas, suggesting that these hybrids are very likely to backcross with wild plants. In general, hybrid plants had fewer branches, flower heads, and seeds than wild plants, but in two crosses the fecundity of hybrids was not significantly different from that of purely wild plants. In Ohio, wild-crop hybrids from North Dakota appeared to be resistant to a rust that infected 53% of the purely wild progeny, indicating a possible benefit of "traditional" crop genes. In summary, our results suggest that F1 wild-crop hybrids had lower fitness than wild genotypes, especially when grown under favorable conditions, but the F1 barrier to the introgression of crop genes is quite permeable.

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 (SBT(0)), it is assumed that only presence or absence of a given allele can be ascertained in a pool; in the second one (SBT(1)), 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. SBT(1) 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.

Sunflower (Helianthus annuus L.) is one of the few crops native to the United States. The current USDA–ARS National Plant Germplasm System (NPGS) crop wild relatives sunflower collection is the largest extant collection in the world, containing 2519 accessions comprising 53 species—39 perennial and 14 annual. To fully utilize gene bank collections, however, researchers need more detailed information about the amount and distribution of genetic diversity present within the collection. The wild species are adapted to a wide range of habitats and possess considerable variability for most biotic and abiotic traits. This represents a substantial amount of genetic diversity available for many agronomic traits for cultivated sunflower, which has a very narrow genetic base. Sunflower ranked fifth highest among 13 crops of major importance to global food security surveyed from the mid‐1980s to 2005 in the use of traits from crop wild relatives. The estimated annual economic contribution of the wild species for cultivated sunflower is between US$267 to 384 million. Most of the value is derived from the PET1 cytoplasm from wild H. petiolaris, disease resistance genes, abiotic salt tolerance, and resistance to imidazolinone and sulfonylurea herbicides. Crop wild relatives provide a wide range of valuable attributes for traditional and molecular breeding, as well as for ecological experimentation, and have enabled rapid advances in ecological and evolutionary genetics. The wild species of Helianthus continue to contribute specific traits to combat emerging pests and environmental challenges and, at the same time, are preserved for future generations.

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Summary• 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.

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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.