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Control of pollen dispersal is critical for the successful coexistence of genetically modified (GM) maize (Zea mays L.) and conventional maize. The impact of climate on cross-pollination by GM pollen was simulated in two field experiments with a color-recessive white-grain receptor DSP17007 and a color-dominant yellow-grain pollen donor in 2005 and 2006. The day after silk exertion of about 2500 marked single plants was taken as the basis for comparing weather data (maximum and minimum temperatures, relative humidity, wind speed, and average wind direction) with data on the cross-pollination of the white-grain receptor. Scattered significant correlations were found for all weather factors; only the minimum temperature at night had consistent negative correlations with rates of cross-pollination ranging from r = -0.22 to -0.45, indicating that the latter decreased as temperatures at night increased. In previous complementary field and growth chamber experiments, the grain set on one inbred line correlated significantly negatively with temperature up to 24 h before pollination (r = -0.55 to -0.66) because of pollen agglutination. This affects medium-distance pollen dispersals to a greater extent than short-distance ones; thus, cross-pollination with GM maize may be lower when the pollen donor has a proclivity for pollen agglutination at a high minimum temperature at night.

Currently recommended minimum isolation distances of 3 and 10 m for pedigreed seed production of annual canarygrass (Phalaris canariensis L.; 2n = 2x = 12) may not be sufficient to maintain the purity of seed lots. The objective of this study was to estimate outcrossing (OC) rates of annual canarygrass over various distances and directions, using the pubescent-hulled trait as a dominant detectable marker. In 2001 and 2002, 5- x 5-m pubescent-hulled pollinator blocks ('Cantate') were sown and surrounded by recipient rows of glabrous-hulled annual canarygrass ('CDC Maria') at Saskatoon, SK. At maturity, 0.5- x 5-m strips were harvested at 0, 0.5, 1, 2, 3, 6, 9, 12, 15, 18, 21, 24, 27, and 30 m along four transects (N, S, E, W) radiating out from the central pollinator block. Outcrossing from Cantate to recipient plants was identified by the expression of trichomes on the hulls of F1 derived seed. In both years, OC rates adjacent to the pollinator did not exceed less than or equal to 2.2%, while OC rates declined rapidly to 0% (2001) or trace levels (0.05%, 2002) at 30 m. Elevated OC to the N of the pollinator was associated with prevailing winds in both years. Maximum OC rates of less than or equal to 2.2% support the suggestion that annual canarygrass is predominantly self-fertilizing. In both years, low OC rates of less than or equal to 0.07% were observed at 24 m, suggesting that currently recommended minimum isolation distances may be inadequate to reduce outcrossed derived off-types to acceptable levels in pedigreed annual canarygrass seed.

Cross-pollination among wheat (Triticum aestivum L.) cultivars historically has not been a major concern for wheat producers. However, with the introduction of genetically engineered wheat, there may be a need to ensure genetic purity, which will require knowledge of the frequency and distance that pollen-mediated gene flow can occur in wheat. This information will be necessary to develop (i) isolation distances that maintain predictable degrees of genetic purity in seed wheat production and (ii) practices to manage pollen-mediated gene flow in commercial wheat production. Field experiments were conducted from 2000 to 2003 at five locations in Oregon, Idaho, and Washington to determine the potential for pollen-mediated gene flow among winter wheat cultivars. Each experiment was designed as a Nelder wheel with 16 equally spaced rays extending away from a central pollen source of blue aleurone wheat. Each ray was 46 m long and contained two rows each of an early- and late-flowering soft white wheat cultivar. Seed samples were collected at 1.8-m intervals along each ray and examined for blue seed, which indicated successful hybridization with the pollen source. Although blue seed was found in some samples at all five locations, most samples (98%) contained no blue seed. Pollen-mediated gene flow generally was in the direction of the prevailing wind and tended to occur more often at the sites with lower temperature and higher humidity during pollination. The maximum distance that gene flow was detected was 42 m from the pollen source and the maximum outcrossing in an individual sample was 0.45%. At four locations, no outcrossing was detected beyond 30 m from the pollen source; however, at one site, 13% of the blue seed was found between 30 and 42 m. Pollen-mediated gene flow potential may differ for other wheat cultivars and environmental conditions. Depending on the required genetic purity standards for wheat seed, an isolation distance of 45 m or more may be required.

There is an increasing concern about the preservation of genetic identity of conventional maize (Zea mays L.) and of distance required to segregate non-genetically modified (non-GM) from GM grain production since the introduction of Bacillus thuringiensis (Bt) and other transgenic events into commercial hybrids. Field experiments were conducted at three sites in Ottawa, Canada, for 3 yr to determine (i) the extent of cross-fertilization of a maize genotype by foreign pollen of neighboring hybrids and (ii) the practical distance required to isolate conventional maize hybrids from neighboring GM maize fields. At each site, yellow-kernel Bt maize was planted in the center (27 by 27 m) of a field surrounded in all directions by the distance equivalent to 24 or 48 rows (37 m) of white-kernel maize, and a 200-m non-maize crop was maintained in all directions. Phenology and weather conditions were closely monitored during the tasseling and silking period. At maturity, a thorough examination on the cross-fertilization was conducted in the white maize population. Our results showed that the rate of cross-fertilization in maize was dependent upon the distance from the pollen source, wind direction and synchronization of silking and pollen shedding of the two genotypes involved. Up to 82% out-cross was measured in the first row adjacent to the Bt maize. The level of out-cross was

Reproductive characteristics can influence seed production and the amount and distribution of genetic variation within populations. Lotononis bainesii Baker is a subtropical forage legume from southern Africa that earlier researchers reported as having a cleistogamous form of reproduction. More recent reports suggest that species in the genus Lotononis Section Listia reproduce chasmogamously. Research from this study suggests that this species needs pollinators to produce seed and that genotypes exist that are self-incompatible. The use of sequence characterized amplified regions (SCAR) and cleaved amplified polymorphic sequence (CAPS) markers demonstrated that L. bainesii is highly allogamous.

To assess genetic and environmental variation for outcrossing in common bean (Phaseolus vulgaris L.), a bulk of nine purplehypocotyled (dominant), black-seeded, common bean lines (pollen parents) and six green-hypocotyled (recessive), white-seeded, common bean lines (seed parents) representing Mexican germplasm were used to estimate outcrossing rate. The experiment was conducted at Irvine and Riverside, CA, in mid-May and mid-July of 1989 and 1991. Outcrossing estimates were based on the proportion of purplehypocotyled progeny from green-hypocotyled parents. Approximately 1400 single-plant families were progeny tested in which 120 278 seedlings were scored for the presence of anthocyanin in the hypocotyl. Of these, 113 246 were classified as selfed progeny and 7031 as hybrid progeny, giving rise to a weighted mean outcrossing rate of 6.9%. Entire progenies from each maternal line were grown and scored, and the minimum and maximum rates of outcrossing observed ranged between 0.0 and 78.0%. Mean outcrossing rate for the six white-seeded lines ranged from 4.41 to 10.16%. However, differences in outcrossing rate among these lines were not significant, nor were differences between dates of planting, locations, or years. The combined analysis of variance showed significant location × planting date × line interaction and year × location × line interaction, indicating that environmental factors had a strong effect on rate of outcrossing in the lines examined. F.J.I.P. acknowledges support from the Consejo Nacional de Ciencia y Tecnologia, Mexico. Research supported in part by California Agric. Exp. Stn., California Dry Bean Board, and USDA, CSRS, Regional Research Project W-150. Part of the dissertation submitted by the senior author in fulfillment of the requirements for the Ph.D. degree.

Faba bean (Vicia faba L.) is a partially allogamous grain legume. Its degree of cross-fertilization (C) is influenced by genetic and environmental effects. Both sources of variation for this trait were investigated in two experiments using black seed color as a morphological marker. Genotypic variation for C among 48 inbred lines derived from the small-seeded European faba bean gene pool was evaluated at one location in Germany for 3 yr (Exp. 1). Environmental variation was evaluated with a subset of four inbred lines grown at 17 European locations, with eight locations evaluated for 2 yr (Exp. 2) [...]

Breeding alfalfa (Medicago sativa L.) with florets that are easier for honey bees (Apis mellifera L.) to trip has been proposed as a means of increasing the efficiency of pollination and improving seed yield, but the impact of selection for ease of tripping on the mating system is not known. This study was conducted to evaluate ease of tripping, self-fertility, and outcrossing rate of alfalfa populations selected for ease of tripping. Easy-to-trip, hard-to-trip, and 'CUF101' parent populations were planted in a randomized complete block design with three replicates at Davis, CA. Ease of tripping of the populations was measured, self-fertility evaluated, and open-pollinated seed harvested in each of two years. The mode of inheritance of the Peroxidase-2 and Fluorescent Esterase-I allozyme loci was verified. Allozyme genotype at these two loci was determined for progeny arrays grown from the open-pollinated seed, and the data used to calculate outcrossing rate of each population using multilocus maximum likelihood estimation procedures. The easy-to-trip population was easier to trip and the hard-to-trip population was harder to trip than the unselected parent population. Self-fertility did not differ among populations. Both Peroxidase-2 and Fluorescent Esterase-I segregated as expected for monomeric enzymes at single tetrasomic loci. The outcrossing rate of the easy-to-trip population (0.76) did not differ from the outcrossing rate of the hard-to-trip population (0.75) or the CUF101 parent population (0.77). Selection for ease of tripping is an easily utilized indirect method which may improve alfalfa seed yield and does not alter the proportion of self-pollinated seed produced

Plant breeders shape breeding and seed increase programs, in part, according to the percent outcrossing in the species. Previous reports indicated that aeschynomene, L., was almost entirely self-pollinated. The objective of these experiments was to determine percent outcrossing under greenhouse and field conditions. A completely dominant trait, glabrousness, was used to determine percent outcrossing in a pubescent line of aeschynomene in the presence of honey bees, spp., in the greenhouse and natural pollinators in the field. Mean percent outcrossing during two seasons in the greenhouse was 24%. Mean percent outcrossing was 30% at two Florida locations separated by 450 km. This level of outcrossing suggests that more rigorous isolation requirements than those currently used may be needed in breeding programs and seed increase fields where two or more lines are grown nearby.