Common lambsquarters is highly competitive in many cropping systems and has demonstrated resistance to several herbicide mechanisms of action. However, predicting the spread of resistance is difficult due to limited information about gene flow. We conducted research to determine the potential for movement of resistance alleles in common lambsquarters under field conditions. Chenopodium giganteum (a member of the C. album aggregate) that has a dominant magenta phenotypic marker was used as a pollen parent in gene flow experiments. A wild-type accession of common lambsquarters was used as a seed parent. Seed parents were grown in a soybean field and arranged in concentric circles 2 to 15 m from a center which contained 24 pollen parents. The concentric circles were divided into eight directions. Pollen movement was estimated by determining the percentage of progeny with the magenta phenotype from seed parents. Average cross-pollination across directions was greatest (3.0%) at 2 m and decreased to low levels (0.16%) 15 m from the center, consistent with observations of other primarily self-pollinated species. Cross-pollination was greatest (P < 0.10) in the south-southwest, west-southwest, and west-northwest directions, approximately 180° from the prevailing wind direction during the time of pollen shed. Since common lambsquarters does not have an active dispersal mechanism for seeds, pollen-mediated gene flow may play an important role in the transfer and frequency of resistance alleles within and between populations.

With the extensive adoption of transgenic crops, an understanding of transgene flow isessential to manage gene flow to non-GM crops. Thus, a flexible and accurate numericalmodel is required to assess gene flow through pollen dispersal. A three-dimensionalatmospheric model combined with a diffusion transport model would be a useful tool forpredicting pollen dispersal since it would be flexible enough to incorporate the effectsof factors such as the spatial arrangement of crop combinations, land use, topography,windbreaks, and buildings. We applied such a model to field measurements of gene flowbetween two adjacent maize (Zea mays) cultivars, with suppression effectsdue to windbreaks, in an experimental cornfield in Japan. This combined model reproducedthe measured cross-pollination distribution quite well in the case of maize plots withplant windbreaks slightly taller than the maize and without windbreaks, but the modelunderestimated the effect of a 6-m-tall windbreak net beyond 25 m from the donor pollensource on cross-pollination. The underestimation was most probably due to the problem ofassimilated wind data. The model showed that the 6-m-tall windbreak and the plant windbreak suppressed average cross-pollination rate by about 60% and 30%, respectively.Half-tall and coarser mesh windbreak net suppressed cross-pollination rates by 40% byreducing the swirl of donor pollen by reduced wind speed.

Modeling pollen dispersal to predict cross-pollination is of great importance for the ongoing discussion of adventitious presence of genetically modified material in food and feed. Two different modeling approaches for pollen dispersal were used to simulate two years of data for the rate of cross-pollination of non-GM maize (Zea mays (L.)) fields by pollen from a central 1 ha transgenic field. The models combine the processes of wind pollen dispersal (transport) and pollen competition. Both models used for the simulation of pollen dispersal were Lagrangian approaches: a stochastic particle Lagrange model and a Lagrangian transfer function model. Both modeling approaches proved to be appropriate for the simulation of the cross-pollination rates. However, model performance differed significantly between years. We considered different complexity in meteorological input data. Predictions compare well with experimental results for all simplification steps, except that systematic deviations occurred when only main wind direction was used. Concluding, it can be pointed out that both models might be adapted to other pollen dispersal experiments of different crops and plot sizes, when wind direction statistics are available. However, calibration of certain model parameters is necessary.

The release of genetically engineered apple trees raises the question of their potential environmental impact, and the transfer via pollen of transgenes to cross-compatible cultivars of Malus domestica and Malus species is deemed to be the greatest source for environmental exposure. The hybrid TNR 31-35, a descendant of Malus sieversii var. sieversii f. niedzwetzkyana, carrying a homozygous, dominant gene responsible for red pigmentation in all plant parts, was used to assess gene flow in an apple scion repository of genetic resources. The red pigmentation provides a morphological marker that enables large-scale evaluation of cross-fertilization under natural conditions. In two consecutive years, 60 and then 56 apple trees of 38 different Malus domestica cultivars were selected to serve as pollen-receptor trees. In these two years, 6876 and then 5513 seeds, respectively, were gathered from pollen-receptor trees located at different distances, 2–100 m from 15 pollen-dispenser trees. In total, 11 797 seedlings were examined. An average of 1.8% and 1.4%, respectively, of all seedlings obtained showed red-colored leaves. Considering both years of sampling, 69% of the seeds fertilized by TNR 31-35 were found at less than 10 m from the nearest pollen-dispenser tree. Almost 91% of all seeds fertilized by TNR 31-35 were found at less than 60 m from the nearest pollen-dispenser tree, which is equal to 30 adjacent trees along the row. In this study, pollen was dispersed at least 104 m. After phenotypical evaluation, seedlings selected as red-colored were investigated by simple sequence repeat (SSR) analysis. Each seedling was tested with at least one heteromorphic SSR-marker, which allows the verification of TNR 31-35 as the male parent. All but four seedlings showed one allele specific for the appropriate fruiting tree and the second allele specific for the pollen-dispenser TNR 31-35.

The orchid family is renowned for its enormous diversity of pollination mechanisms and unusually high occurrence of non-rewarding flowers compared to other plant families. The mechanisms of deception in orchids include generalized food deception, food-deceptive floral mimicry, brood-site imitation, shelter imitation, pseudoantagonism, rendezvous attraction and sexual deception. Generalized food deception is the most common mechanism (reported in 38 genera) followed by sexual deception (18 genera). Floral deception in orchids has been intensively studied since Darwin, but the evolution of non-rewarding flowers still presents a major puzzle for evolutionary biology. The two principal hypotheses as to how deception could increase fitness in plants are (i) reallocation of resources associated with reward production to flowering and seed production, and (ii) higher levels of cross-pollination due to pollinators visiting fewer flowers on non-rewarding plants, resulting in more outcrossed progeny and more efficient pollen export. Biologists have also tried to explain why deception is overrepresented in the orchid family. These explanations include: (i) efficient removal and deposition of pollinaria from orchid flowers in a single pollinator visit, thus obviating the need for rewards to entice multiple visits from pollinators; (ii) efficient transport of orchid pollen, thus requiring less reward-induced pollinator constancy; (iii) low-density populations in many orchids, thus limiting the learning of associations of floral phenotypes and rewards by pollinators; (iv) packaging of pollen in pollinaria with limited carry-over from flower to flower, thus increasing the risks of geitonogamous self-pollination when pollinators visit many flowers on rewarding plants. All of these general and orchid-specific hypotheses are difficult to reconcile with the well-established pattern for rewardlessness to result in low pollinator visitation rates and consequently low levels of fruit production. Arguments that deception evolves because rewards are costly are particularly problematic in that small amounts of nectar are unlikely to have a significant effect on the energy budget of orchids, and because reproduction in orchids is often severely pollen-, rather than resource-limited. Several recent experimental studies have shown that deception promotes cross-pollination, but it remains unknown whether actual outcrossing rates are generally higher in deceptive orchids. Our review of the literature shows that there is currently no evidence that deceptive orchids carry higher levels of genetic load (an indirect measure of outcrossing rate) than their rewarding counterparts. Cross-pollination does, however, result in dramatic increases in seed quality in almost all orchids and has the potential to increase pollen export (by reducing pollen discounting). We suggest that floral deception is particularly beneficial, because of its promotion of outcrossing, when pollinators are abundant, but that when pollinators are consistently rare, selection may favour a nectar reward or a shift to autopollination. Given that nectar-rewardlessness is likely to have been the ancestral condition in orchids and yet is evolutionarily labile, more attention will need to be given to explanations as to why deception constitutes an ‘evolutionarily stable strategy’.