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Gene flow in wheat at the field scale.

THE POTENTIAL for pollen-mediated gene escape over long distances is a concern associated with the release of transgenic wheat (Triticum L.) cultivars. A range of genetically engineered genes have been introduced into wheat (Janakiraman et al., 2002), but no commercial release has been reported to date. In anticipation of the release of genetically engineered wheat, field trials are currently being conducted to understand gene flow and agronomic issues surrounding the potential adoption of transgenic wheat. Research to date has not measured gene flow, the exchange of genes between different but usually related populations, over longer distances in wheat. In wheat, successful gene flow depends upon the receptivity of the stigmas, the viability of the pollen, and availability of pollen during the receptive period (Johnson and Schmidt, 1968; Waines and Hegde, 2003). These factors vary with genotype and environment (de Vries, 1971, 1972, 1974).

The occurrence of intra- and interspecific gene flow in wheat and the tendency for some cultivars to possess higher gene flow rates than others is well established. Wheat is a predominantly self-pollinating crop with a gene-flow rate of usually less than 1% (Johnson and Schmidt, 1968). Heyne and Smith (1967) reported that the extent of gene flow in commercial wheat cultivars ranged from 0 to 4% in close proximity. Higher gene flow rates including 0.1 to 5.6% (Martin, 1990) and 0.3 to 6.1% (Hucl, 1996) have been reported in wheat with plants grown in close proximity. A number of studies have observed off-types in wheat cultivars attributable to gene flow between wheat genotypes of the same species (Appleyard et al., 1979; Porter et al., 1980; Griffin, 1987; Takahasi and Isii, 1988). Interspecific gene flow rates have been studied to a limited extent. Zorun-Ko et al. (1996) reported interspecific gene flow rates of 0.04 to 0.30% from common hexaploid (T. aestivum; 2n = 6x = 42 chromosomes; BBAADD) to durum wheat (T. turgidum; 2n = 4x = 28 chromosomes; BBAA), with plants grown in close proximity. Research has indicated that low male fertility is generally associated with cultivars possessing higher gene-flow rates (Hucl, 1996; Ingram, 2000; Hucl and Matus-Cadiz, 2001). Attempts have been made to associate increased gene flow with specific plant traits such as plant height (Martin, 1990; Briggs et al., 1999) and spike characteristics (de Vries, 1971; Hucl, 1996), but no single trait has been useful in predicting whether cultivars will possess gene flow rates >1%.

Gene flow in wheat has been studied at distances of less than 48 m and has centered on the production of hybrid wheat, which has little application to most current agronomic production systems. Various studies have reported seed set on target male sterile lines at 5 to 48 m from a known pollen source (Bitzer and Patterson, 1967; Wilson, 1968; Jensen, 1968; Zeven, 1968; de Vries, 1974; Khan et al., 1973; Miller et al., 1975). Jensen (1968) reported that pollen could travel as far as 60 m. Pollen loads generally remained concentrated within 3 to 8 m of their pollen source and decreased with greater distance from the pollinator. We have detected an intraspecific gene flow rate of 0.03 to 0.09% for two male fertile common wheat cultivars at a distance of 27 m over cropped soil using a blue-grained pollinator (Hucl and Matus-Cadiz, 2001). Sampling did not extend beyond 33 m and, consequently, we speculate that low levels of gene flow may occur at distances beyond 33 m with heavier pollen loading. To date, gene flow in wheat has been studied in small-sized pollinator blocks (e.g., 5 by 5 m) located within close proximity of recipient plants.

Larger-scale field studies are needed to measure the level of pollen-mediated gene flow that may exist in larger-sized pollinator blocks located at varying distances from recipient plants. Transgenic plants with a marker gene, such as herbicide resistance, have commonly been used for investigating pollen dissemination in controlled experimental fields trials (Ingram, 2000). Our research proposes to measure gene flow over long distances in wheat in a 50- by 50-m pollinator block, with the blue-aleurone trait as a detectable marker (Keppenne and Baenziger, 1990). The blue-grained trait is a dominant gene marker that has been applied to studying small-scale gene flow (Hucl and Matus-Cadiz, 2001). Cross-pollination from blue-seeded to non-blue-seeded wheat is identified by the expression of a light-blue pigment in the triploid aleurone layer of [F.sub.1] seed. An understanding of the distance and frequency to which pollen-mediated gene flow can occur will provide information useful for (i) risk assessments considering gene-escape from transgenic to nontransgenic wheat, (ii) developing guidelines for maintaining line purity in breeding programs and pedigreed seed production, and (iii) developing strategies for managing gene flow between commercial fields. The objectives of this research were to measure gene flow rates from a blue grained pollinator Purendo-38 to (i) red-grained spring wheat cv. CDC Teal over distances of 0.2 to 160 m, (ii) amber durum wheat cv. AC Navigator over distances of 0.2 to 260 m, and (ii) CDC Teal and AC Navigator over distances of 180 to 2760 m.

MATERIALS AND METHODS

Breeder seed of Purendo-38, a spring type blue-grained wheat (Abdel-Aal and Hucl, 1999) and CDC Teal, a Canada Western Red Spring wheat cultivar (Hughes and Hucl, 1993), were obtained from the Crop Development Center, Saskatoon, SK. Certified seed of AC Navigator, a Canada Western Amber Durum cultivar (Clarke et al., 2000), was obtained from the Saskatchewan Wheat Pool.

Wheat genotypes carrying the blue aleurone trait were not documented until the artificial introgression of genes from Agropyron species (Zeven, 1991). Therefore, the blue-aleurone trait was not expected to be present in the genetic background of CDC Teal or AC Navigator. Seed lots of CDC Teal and AC Navigator used in 2001 were screened for the presence of blue-aleurone seed. Blue-aleuroned seed was not observed during the screening of 50 000 seeds of each cultivar. In 1990, a bulk population of spring wheat segregating for male-sterility and blue-aleurone, introgressed from an unknown accession of Agropyron elongatum (Host) Beauv., was obtained from Dr. D. Falk (Dep. of Crop Sci., University of Guelph, Guelph, ON). This bulk population was increased in bulk at Saskatoon, SK in 1990 and 1991. In 1992, 2000 blue seeds were handpicked and space-planted. Approximately 600 individual spikes were harvested based on reduced shattering. Of the 600 spikes, seed from 180 spikes were homogeneous for the blue-grained trait. In 1993, seed from the 180 spikes were grown in head-rows and 53 rows were determined to be homozygous for the blue-grained trait. Purendo-38 was selected from the most promising 10 homozygous lines tested over three years based on its grain color, quality, and agronomic traits. The stability of the blue-aleurone trait in Purendo-38 was verified by evaluating grain samples from 200 head-rows. Purendo-38 has been stable for the blue-aleurone trait over six generation of testing.

Intraspecific Gene Flow

In 2000 and 2001, 400 x 400-m field trials were sown in separate fields at the Kernen Crop Research Farm (KCRF), University of Saskatchewan, Saskatoon, SK. The experiment consisted of a central blue-grained pollinator block (50 by 50 m) surrounded by CDC Teal to a distance of 175 m in all directions (Fig. 1). Recipient rows were spaced 0.2 m apart. The pollinator block was seeded at a low rate (100 seeds [m.sup.-2]) over two seeding dates in alternating strips. Strips consisted of eight rows, 50 m long and 0.2 m apart. Pollinator blocks were sown on 1 May (1st planting date) and 8 May (2nd planting date) in 2000 and 24 April (1st planting date) and 2 May (2nd planting date) in 2001. The reduced seeding rate and dual seeding dates of the pollinator block were used to promote "nicking" between the two genotypes. CDC Teal was sown on 3 May 200(1 and 2 May 2001 at a rate of 250 seeds [m.sup.-2] on fallow land. Seeds were treated with the systemic fungicide Vitavax Single Solution (Uniroyal Chemical Ltd., Elmira, ON; active ingredient carbathiin, 5-dihydro-2-methyl-N-phenyl 1,4,oxathiin-3-carboximide) at the recommended rate. Fertilizer was drilled in with the seed at a rate of 7 kg [ha.sup.-1] of N and 29 kg [ha.sup.-1] of P. The soil type was a Dark Brown Chernozem (Typic boroll) Sutberland clay, clay-loam at the KCRF. Plant height, days to heading (date of 50% spike emergence), and duration of flowering (days between the first and last observed occurrence of anthesis) were collected. Data for the pollinator block were averaged over values collected at the random positions within each seeding date. Data for CDC Teal were averaged over values collected at eight positions (0.2, 25, 50, 75, 100, 125, 150, and 175 m from the pollinator) in each of four directions (N, E, S, and W). Meteorological data were collected within 3 km of the trial site by Environment Canada.

[FIGURE 1 OMITTED]

At maturity, 0.5- by 4-m strips of CDC Teal were sickled and bagged at 0.2, 1, 5, 10, 20, 40, 60, 80, 100, 120, 140, and 160 m along eight transects (N, E, S, W, NE, SE, SW, NW) radiating out from the 50- by 50-m square pollinator block (Fig. 1). Strips were harvested perpendicularly to the sides and corners of the pollinator block. Samples were dried 24 h in large forced air driers set at 35[degrees]C and subsequently threshed with a small plot combine. Samples were sorted before threshing on the basis of transect and distance. Samples harvested within each transect were threshed in descending order starting with the sample most distant from the pollinator source. A 2- by 2-m quadrant sample of barley (Hordeum vulgare L.) was threshed to clean the combine between samples from different transects. Eight thousand seeds were counted per sample with an ESC-1 electronic seed counter (model ESC120001, Agriculex Inc, Guelph, ON).

Cross-pollination events from Purendo-38 to recipient plants of CDC Teal were identified by the expression of a light-blue pigment in the aleurone layer of [F.sub.1] seed. Seeds suspected of possessing a light-blue aleurone were visually identified and kept separate from the remaining seed lot. Putative light blue seeds were sown in the greenhouse. Resulting plants were grown to maturity to confirm visual identifications as putative light blue seeds can be confused with discolored seeds because of disease or weathering, and immature seeds. Seeds were surface sterilized for 8 min in a solution of 2.5% (v/v) sodium hypochlorite and 0.1% (v/v) Tween 20, rinsed for 5 min with water, rinsed once with 70% (v/v) ethanol, and subsequently air-dried. Seeds were germinated at 15[degrees]C (in darkness) for 10 d in a Petri-dish (each containing a Whatman No.1 filter paper) before transferring to soil. Pregerminated seeds were planted (2.5-cm depth) in 15-cm-diameter pots (one plant per pot). Pots were filled with Terra-Lite Redi-Earth (W.R. Grace and Co. of Canada Ltd. Ajax, ON). Greenhouse conditions were set to 24/18[degrees]C (day/night) with 18 h light and a photosynthetically active radiation level of 250 [micro]mol [m.sup.-2] [s.sup.-1]. Plants were watered every 4 d and fertilized with Type 100 Nutricote controlled release granular fertilizer (14-14-14) (Plant Products Co. Ltd. Brampton, ON) at a rate of 0.8 kg [m.sup.-2]. Segregation among [F.sub.1]-derived [F.sub.2] seed was classified as segregating (3 blue: 1 non-blue seed ratio) or nonsegregating (all non-blue seeds) for the blue-aleurone trait.

There were 512 putative light blue seeds identified in 2000 and 213 seeds identified in 2001. The percentage of putative light blue seeds that developed to produce established plants for verification purposes was 64% in 2000 and 65% in 2001. None of the established plants produced only blue-aleuroned seed, indicating that seed admixture was not a source of contamination within this study. The number of established plants confirmed to be segregating for the blue-aleurone trait was 303 plants (59%) in 2000 and 127 plants (60%) in 2001. Unconfirmed gene flow rates were calculated as follows: gene flow (%) = (total number of putative light blue seeds observed in [s.sub.i] at [d.sub.j]/8000 seeds of [s.sub.i] at [d.sub.j]) x 100 where [s.sub.i] is the ith sample and [d.sub.j] is the jth distance. Confirmed gene flow rates were calculated as follows: gene flow (%) = (total number of confirmed light blue seeds observed in [s.sub.i] at [d.sub.j]/8000 seeds of [s.sub.i] at [d.sub.j]) x 100 where total number of confirmed light blue seeds is defined as the total number of putative light blue seeds verified to produce [F.sub.1] plants segregating for the blue-aleurone trait. Confirmed gene flow rates were expected to be lower than unconfirmed rates as less than 100% of putative light blue seeds germinated to produce established plants for verification purposes. This difference may be explained, in part, by the fact that diseased, weathered, and immature seeds are unlikely to germinate and grow to produce plants. Of the putative light blue seeds failing to produce an established plant, the proportion of these putative seeds that would have shown segregation or nonsegregation for the blue-aleuroned trait is unknown.

Interspecific Gene Flow

The same experimental design as described above was modified as follows for the interspecific gene flow experiment. In 2000 and 2001, 650- by 650-m field trials were sown in separate fields at the KCRF, University of Saskatchewan approximately 2 km from the intraspecific gene flow experiments. The experiment consisted of a central Purendo-38 pollinator block (50 by 50 m) surrounded by AC Navigator to a distance of 275 m in all directions (Fig. 1). The pollinator block was sown as described above. AC Navigator was seeded on 5 May 2000 and 4 May 2001 at a rate of 250 seeds [m.sup.-2] on fallow land. Plant height, days to heading, and duration of flowering were calculated for AC Navigator by collecting data at 10 positions (0.2, 25, 50, 75, 100, 125, 150, 175, 200, and 225 m from the pollinator) in each of four directions (N, E, S, and W). At maturity, 0.5- by 4-m strips of AC Navigator were sickled and bagged at 0.2, 1, 5, 10, 20, 40, 60, 80, 100, 120, 141), 160, 180, 200, 220, 240, and 260 m along eight transects (N, E, S, W, NE, SE, SW, NW) radiating out from the 50- by 50-m square pollinator block. Strips were harvested perpendicular to the sides and corners of the pollinator block. Spike samples were threshed using a rubber-belted de-awner. The wind-speed on the de-awner was turned off to retain shriveled seed, and consequently, chaff within samples was removed manually. Samples were sorted before threshing on the basis of transect and distance. Samples harvested within each transect were threshed in descending order starting with the sample most distant from the pollinator source. A 2- by 2-m quadrant sample of barley was threshed to clean the combine between samples from different transects.

Cross-pollination from Purendo-38 to recipient plants of AC Navigator were identified by the expression of a light-blue pigment in the aleurone layer of shriveled [F.sub.1] hybrid seed. Shriveled seeds suspected of possessing a light-blue aleurone were visually identified and confirmed by greenhouse grown-outs. The number of putative light blue seeds identified was 893 seeds in 2000 and 127 seeds in 2001. The percentage of putative light blue seeds that developed to produce established plants was 21% in 2000 and 41% in 2001. The number of established plants confirmed to be segregating for the blue-aleurone trait was 107 plants (12%) in 2000 and 52 plants (41%) in 2001.

Long-Distance Intra- and Interspecific Gene Flow

All CDC Teal and AC Navigator fields seeded at the KCRF, University of Saskatchewan were screened for light blue seeds. Breeder-derived seed of CDC Teal and certified seed of AC Navigator were used as seed sources. A total of 38 and 39 random samples were collected in 2000 and 2001, respectively. At each sampling site, a 0.5- by 4-m strip was sickled, bagged, dried, and subsequently threshed. Seeds suspected of possessing a light-blue aleurone were visually identified and confirmed using greenhouse grown outs. In 2000, the number of putative light blue seeds identified was 14 seeds (CDC Teal) and five seeds (AC Navigator). The percentage of putative light blue seeds that developed to produce established plants was 57% (CDC Teal) and 0% (AC Navigator). One established plant was confirmed to be segregating for the dominant gene marker. In 2001, seven putative light blue seeds were identified with none of them developing to produce established plants. Unconfirmed gene flow rates were calculated as follows: gene flow (%) = (total number of putative light blue seeds observed in [s.sub.i] at [d.sub.j]/total number of seeds harvested of [s.sub.i] at [d.sub.j]) x 100. Confirmed gene flow rates were calculated as follows: gene flow (%) = (total number of confirmed light blue seeds observed in [s.sub.i] at [d.sub.j]/total number of seeds harvested of [s.sub.i] at [d.sub.j]) x 100.

RESULTS

Intraspecific Gene Flow

The 9-d pollination period in 2000 was generally cooler, more humid, and wetter than the 9-d pollination period in 2001 (Table 1). In 2000, average heading date for CDC Teal was 6 July and for Purendo-38 was 9 July (1st planting date) and 11 July (2nd planting date). The estimated duration of flowering was 11 d for CDC Teal (5% anthesis on 9 July to 95% on 19 July) and 18 d for Purendo-38 (5% anthesis on 11 July to 95% on 28 July). The estimated over-lap in pollination periods between CDC Teal and Purendo-38 was about nine days (11-19 July) (Table 1). Prevailing winds were from the E, SE, and ESE during 4 d (averaging 16 km [h.sup.-1]) and from the W, WNW, or NE during the remaining 5 d (averaging 15 km [h.sup-1]) of pollination (Table 1). Daily mean wind speed during pollination was 17 km [h.sup.-1] (range = 9-26 km [h.sup.-1]). Daily mean temperature, relative humidity, and precipitation values were 17[degrees]C (range = 12-24[degrees]C), 75 % (range = 59-89%), and 1.0 mm (range = 0-4.5 mm) during pollination, respectively.

In 2001, average heading date for CDC Teal was 30 June and for Purendo-38 was 26 June (1st planting date) and 30 June (2nd planting date). The estimated duration of flowering was 9 d for CDC Teal (5% anthesis on 5 July to 95% on 13 July) and 13 d for Purendo-38 (5%0 anthesis on 1 July to 95% on 13 July. The estimated over-lap in pollination periods between CDC Teal and Purendo-38 was about 9 d (5-13 July) (Table 1). Prevailing winds were from the W for 2 d (averaging 19 km [h.sup.-1]), SSE and S for 3 d (averaging 22 km [h.sup.-1]), and N, NE, or ENE for the remaining 4 d (averaging 12 km [h.sup.-1]) of pollination. Mean wind speed during pollination was 17 km [h.sup.-1] (range = 11-27 km [h.sup.-1]). Mean temperature, relative humidity, and precipitation values were 21[degrees]C (range = 19-25[degrees]C), 62% (range = 42-81%), and 0.03 mm (range = 0-0.3 mm) during pollination, respectively. Plant heights for Purendo-38 (101 cm; SE [+ or -] 2) and CDC Teal (97 cm; SE [+ or -] 2) were similar over years. The pollination periods observed in 2000 and 2001 were expected to ensure a good level of nicking between recipient and pollinator plants. The periods of over-lap in this study may be a conservative estimate as the stigma of male-fertile plants are known to be receptive for a period of 4 to 13 d (de Vries, 1971).

Confirmed gene flow rates were higher in 2000 compared with 2001 (Table 2). Unconfirmed gene flow rates are presented in Table 2 to indicate the furthest distance from the pollinator at which putative light blue seeds were detected. In 2000, maximum confirmed gene flow rates for CDC Teal were equal to, or less than, 0.44%. Percent gene flow declined rapidly as distance increased and leveled off at trace levels ([less than or equal to] 0.01%) beyond 60 m. Percent gene flow (averaged over eight directions) was 0.20% at 0.2 m, 0.17% at 1 m, and decreased to 0.003% by 100 m. Percent gene flow at 0.2 m ranged from a low of 0.08 (east of the pollinator) and 0.09% (SE) to a high of 0.30% (N), 0.34% (W), and 0.41% (NW). No gene flow was detected at or beyond 120 m. Approximately 78% and 99% of cumulative gene flow occurred within one and 40 m of the pollinator, respectively. Average gene flow (0.2-100 m) within directions was determined to identify the primary directions in which gene flow occurred. Out-crossing (averaged over nine distances) was highest to the NW of the pollinator (0.12%) followed by the W (0.11%) and N (0.09%) directions. Gene flow (averaged over nine distances) was detected at trace levels ([less than or equal to] 0.04%) to the NE, E, SE, S, and SW of the pollinator. Gene flow levels equal to or greater than 0.01% were detected at 0.2 m (SW), 20 m (W, NE, and SE),

40 m (E and S), and 100 m (N and NW) from the pollinator. Approximately 76% of cumulative gene flow occurred to the N, W, and NW of the pollinator. Prevailing wind direction was associated with elevated gene flow rates to the N, W, and NW of the pollinator during 4 of 9 d (44%) of pollination (Tables 1 and 2).

In 2001, maximum confirmed gene flow rates for CDC Teal were equal to or less than 0.24% (Table 2). Percent gene flow declined rapidly as distance increased and leveled off at trace levels ([less than or equal to] 0.01%) at and beyond 60 m. Percent gene flow (averaged over eight directions) was 0.08% at 0.2 m, 0.06% at 1 m, and decreased to 0.002% by 80 m. Percent gene flow at 0.2 m ranged from a low of 0.01% (S and SE) to a high of 0.13% (N), 0.24% (E), and 0.11% (W). No gene flow was detected at or beyond 100 m. Approximately 79 and 99% of cumulative gene flow occurred within 5 and 40 m of the pollinator, respectively. Gene flow rates (averaged over nine distances) were highest to the east of the pollinator (0.07%). Gene flow was detected at trace levels ([less than or equal to] 0.04%) in the remaining seven directions. Gene flow levels equal to or greater than 0.01% were detected at 1 m (S), 5 m (N, NE, and SW), 10 m (W and NW), 40 m (SE), and 80 m (E) from the pollinator. Approximately 83% of cumulative gene flow occurred to the N, E, W, and NW of the pollinator. Prevailing wind direction was associated with elevated gene flow rates to the east of the experiment for only 2 of 9 d (22%) of pollination (Tables 1 and 2).

Interspecific Gene Flow

The 11-d pollination period in 2000 was generally longer in duration, cooler, more humid, and wetter relative to the 7-d pollination period in 2001 (Table 1). In 2000, average heading date for AC Navigator was 9 July and for Purendo-38 was 10 July (1st planting date) and 12 July (2nd planting date). The estimated duration of flowering was 12 d for AC Navigator (5% anthesis on 11 July to 95% on 22 July) and 17 d for Purendo-38 (5% anthesis on 12 July to 95% anthesis on 28 July). The estimated over-lap in pollination periods between AC Navigator and Purendo-38 was about 11 d (12-22 July) (Table 1). Daily mean wind speed during 11 d of pollination was 15 km [h.sup.-1] (range = 5-26 km [h.sup.-1]). Prevailing winds were from the E, SE, and ESE during six days (averaging 14 km [h.sup.-1]) and from the W, WNW, or N during the remaining 5 d (averaging 16 km [h.sup.-1]) of pollination. Daily mean temperature, relative humidity, and precipitation values were 17[degrees]C (range = 12-24[degrees]C), 74% (59-89%), and 0.8 mm (04.5 mm) during pollination, respectively.

In 2001, average heading date for AC Navigator was 4 July and for Purendo-38 was 2 July (1st date) and 4 July (2nd date). The estimated duration of flowering was 10 d for AC Navigator (5% anthesis on 7 July to 95% on 16 July) and 9 d for Purendo-38 (5% anthesis on 5 July to 95% on 13 July). The estimated over-lap in pollination periods between AC Navigator and Purendo-38 was about 7 d (7-13 July) (Table 1). Prevailing winds were from the SSE for 2 d (averaging 19 km [h.sup.-1]), the W for 1 d (14 km [h.sup-1]), and the N, NE, or ENE for the remaining 4 d (averaging 12 km [h.sup.-1]) of pollination. During the seven days of pollination, mean wind speed was 14 km [h.sup.-1] (range = 11-20 km [h.sup.-1]), mean temperature was 21[degrees]C (range = 19-23[degrees]C), relative humidity was 66% (range = 56-81%), and mean precipitation was 0.04 mm (range = 0-0.3 mm). Plant heights for Purendo-38 (98 cm; SE [+ or -] 2) and AC Navigator (76 cm; SE [+ or -] 1) were similar over years. The pollination periods observed in 2000 and 2001 were expected to ensure a good level of nicking between recipient and pollinator plants.

Generally, confirmed gene flow rates observed in 2000 were higher than in 2001 (Table 3). In 2000, maximum gene flow rates for AC Navigator were equal to or less than 0.19% (Table 3). Percent gene flow declined rapidly as distance increased and leveled off at trace levels ([less than or equal to] 0.05%) beyond 20 m. Percent gene flow (averaged over directions) was 0.08% at 0.2 m and decreased to 0.01% by 20 m. Percent gene flow at 0.2 m ranged from a low of 0.01% (SE) to a high of 0.10% (NW), 0.11% (N and S), and 0.14% (W). No gene flow was detected at or beyond 40 m. Approximately 71 and 94% of cumulative gene flow occurred within 1 m and 10 m of the pollinator, respectively. Gene flow rates (averaged over five distances) were highest to the north of the pollinator (0.08%) followed by the west (0.05%), and northwest (0.05%). Gene flow was detected at trace levels ([less than or equal to] 0.04%) to the NE, E, SE, S, and SW of the pollinator. Gene flow levels of equal to of greater than 0.01% were detected at 0.2 m (NE and SW), 5 m (E), 10 m (S, W, and NW), and 20 m (N and SE) from the pollinator. Approximately 64% of cumulative gene flow occurred to the N, W, and NW of the pollinator. Wind direction was associated with elevated gene flow rates to the N, W, and NW of the pollinator during 6 of 11 d (55%) of pollination (Tables 1 and 3).

In 2001, maximum confirmed gene flow rates for AC Navigator were equal to or less than 0.11% (Table 3). Percent gene flow declined rapidly as distance increased and leveled off at trace levels ([less than or equal to] 0.01%) by 20 m. Percent gene flow (averaged over directions) was 0.05% at 0.2 m and decreased to 0.002% by 20 m. Percent gene flow at 0.2 m ranged from a low of zero (E) to a high of 0.08% (W) to 0.10% (N). No gene flow was detected beyond 40 m. Approximately 54 and 98% of cumulative gene flow occurred within 0.2 and 5 m of the pollinator, respectively. Gene flow rates (averaged over five distances) were highest to the north of the pollinator (0.04%) followed by the seven remaining directions ([less than or equal to] 0.02%). Gene flow levels of [greater than or equal to] 0.01% were detected at 0.2 m (S), 1 m (N, SE, SW, and W), 5 m (NE and E), and 20 m (NW) from the pollinator. Approximately 56% of cumulative gene flow occurred to the N, W, and NW of the pollinator. Prevailing wind direction was associated with elevated gene flow rates to the N, W, and NW of the experiment for only 2 of 7 d (29%) of pollination (Table 1 and 3).

Long-Distance Intra- and Interspecific Gene Flow

Long-distance intraspecific pollen-mediated gene flow was not detected beyond 300 m of the pollinator blocks (Table 4). In 2000, a trace level of long-distance intraspecific gene flow was confirmed in one of 34 samples of CDC Teal. That is, a trace gene flow rate of 0.005% was detected in CDC Teal sampled at 300 m to the NW of the pollinator. The detection of this intraspecific seed was observed within the 400- by 400-m experimental field of CDC Teal and not within an adjacent field. This gene flow occurrence was associated with prevailing winds and the elevated gene flow rates to the NW of the pollinator (Tables 1 and 2). In 2001, long-distance intraspecific gene flow was not confirmed in any of the 34 samples of CDC Teal screened. Long-distance interspecific gene flow was not confirmed in any of the four AC Navigator samples screened in 2000 or any of the six samples screened in 2001 (Table 4).

DISCUSSION

Pollen dispersal during flowering varies with plant height (de Vries, 1972), spike morphology such as the awnedness of the lemma (de Vries, 1971), and cultivar (de Vries, 1972; Hucl, 1996). Purendo-38, an awnless cultivar, was similar in plant height to CDC Teal, an awnless cultivar, indicating that the height of the pollinator source relative to CDC Teal was probably not a major factor in promoting the downward dispersal of pollen onto recipient plants in the field. In contrast, Purendo-38 was taller relative to AC Navigator, a semi-dwarf awned cultivar. This difference in plant height may have promoted the downward dispersal of pollen from taller pollinator plants onto recipient plants in the field. In contrast, the awned spikes of AC Navigator may have depressed gene flow rates in our experiment as research in hybrid wheat production has shown that the free-falling movement of pollen is impeded by the awns of male-sterile plants (de Vries, 1971). Interspecific barriers to hybridization were probably of greater importance in impeding gene flow rates. Hybrid wheat research suggests that awnless recipient and pollinator plants should be used to produce maximum seed set in male-sterile plants (de Vries, 1971). To date, CDC Teal and AC Navigator have not been characterized for their tendency to out-cross. Hucl (1996) classified 10 Canadian spring wheat cultivars as possessing a low or high tendency toward gene flow. Our research has indicated that low floret fertility is generally associated with cultivars possessing higher gene-flow rates (Hucl, 1996; Hucl and Matus-Cadiz, 2001). Further research is needed to determine the tendency of wheat cultivars toward floret infertility and gene flow. Lower levels of pollen-mediated gene movement in wheat could theoretically be achieved with wheat cultivars with low tendencies toward floret infertility and, thus, out-crossing. However, this would not limit gene flow mediated by other means (e.g., human and animal).

Pollen dispersal during flowering varies with environmental factors such as prevailing winds, wind speed, temperature, humidity, and precipitation (de Vries, 1971, 1972, 1974). Gene flow was generally dependent on wind direction during the flowering period of the crop (Tables 2 and 3). In 2000, elevated gene flow rates were generally observed to the N, W, and NW of the pollinator. Wind direction and gene flow rates showed a weaker association in 2001 compared with 2000, indicating that gene flow rates should not be based on experiments oriented in only one direction from the pollinator. Pollination periods in 2001 were generally hotter, less humid, and drier relative to pollination periods in 2000, indicating that the elevated gene flow rates observed in 2000 were probably promoted by cooler, more humid, and wetter conditions. De Vries (1972) reported that the highest concentration of pollen dispersal appeared to be released at a temperature of 16 to 20 [degrees]C and relative humidity of 70 to 75%. Wheat pollen grains have been reported to be viable for 15 to 20 min, or up to 30 min under optimal conditions (de Vries, 1971). In the present study, the weather conditions in 2000 fall within the optimum range reported by de Vries (1972). Environmental conditions from year to year are considered random factors of factors that cannot be controlled be the researcher. Consequently, the weather conditions in some years will promote relatively high gene flow rates and conditions in other years will depress gene flow rates.

Intra- and interspecific pollen-mediated gene flow rates remained below 0.5% and declined rapidly with distance from the pollinator. Confirmed intraspecific pollen mediated gene flow rates declined from 0.44 to 0.01% over a distance of 100 m from the pollinator in 2000 (Table 2). In 2001, confirmed gene flow rates declined from 0.24 to 0.01% over a distance of 80 m from the pollinator. In both years, intraspecific gene flow declined to trace levels ([less than or equal to] 0.01%) by 60 m from the pollinator. Confirmed interspecific pollen mediated gene flow rates declined from 0.19% to 0.05% in 2000 and from 0.11 to 0.01% in 2001 over a distance of 20 m from the pollinator (Table 3). Interspecific gene flow declined to trace levels of [less than or equal to] 0.05% in 2000 and [less than or equal to] 0.01% in 2001 by 20 m from the pollinator. In Canada, a maximum impurity tolerance of 0.01% (one off-type per 10 000 plants x 100) in Foundation or Registered seed and 0.05% in Certified seed has been deemed acceptable in wheat production (Anonymous, 1994). Minimum isolation requirements, from another genotype of the same wheat species, of 3 m for the production of Foundation, Registered, or Certified seed are currently recommended. Recently, we recommended increasing the isolation distance from 3 m to at least 30 m to mitigate out-crossed derived off-types in the subsequent generation of pedigreed seed (Hucl and Matus-Cadiz, 2001). Our current results, based on a 50- by 50-m pollen source, support our earlier findings, based on a small 5- by 5-m pollen source (Hucl and Matus-Cadiz, 2001), that an isolation distance of at least 30 m may be required to limit off-type impurities to 0.01%.

One case of long-distance intraspecific pollen-mediated gene flow was confirmed at a rate of 0.005% at a distance of 300 m to the NW of the 2000 pollinator block (Table 4). This gene flow event probably resulted from wind-mediated pollen movement promoted by strong and prevalent winds. The possibility of insect-mediated pollen movement cannot be discarded, but the amount of insect pollination, if any, in wheat is currently not known. The detection of trace gene flow rates at distances of 300 m from the pollinator field suggest that attaining 100% genetic purity in pedigreed seed lots is unattainable without geographic separation. Another implication of these findings is that geographic separation of wheat with various novel traits or genetic backgrounds, including transgenic and nontransgenic material, may be required for maintaining purity within breeding programs. Genetic purity of breeder, select, foundation, registered, and certified seed is of great importance since the degree of impurity within these seed lots, used to produce pedigreed seed of establish a commercial crop, can become a source from which crop cultivars can become contaminated with novel traits.

The genetic stability, fitness, and fertility of hybrids have been listed as important factors affecting gene flow in plants (Barton and Dracup, 2000). Intraspecific pollen mediated gene flow was confirmed over longer distances from the pollinator compared with interspecific gene flow (Tables 2, 3, and 4). The shrunken endosperm of the interspecific hybrids, unlike the fully developed endosperm of intraspecific hybrids, probably reduces the possibility of gene introgression in subsequent generations because of reduced seedling establishment. Little research is available regarding the stability, fitness, and fertility of intra- and interspecific wheat hybrids. Our study will be useful in assessing the risk posed by transgenic wheat cultivars. When considering the risk posed by the introduction of a new wheat cultivar, the distance and frequency to which pollen mediated gene flow occurs is considered, as is any potential ecological consequence of gene transfer.

Pollen dispersal during flowering varies with pollinator field size (de Vries, 1974). Hybrid wheat production studies have studied optimum sizes of pollinator blocks for cross-pollination. These studies generally use small pollinator plots and, thus, have limited application in estimating the amount of gene flow taking place between commercial-scale fields. Caution must be applied to extrapolating the gene flow rates reported in the present study to larger-scale field studies using commercial-scale pollinator sources because our study may underestimate the level of gene flow rate that may be occurring between commercial-scale fields. In addition, trace gene flow rates of 0.005% may occur at distances exceeding 300 m from commercial-scale pollinator sources. Further research is needed to determine the level of gene flow occurring between neighboring commercial-scale wheat fields.

In summary, our results suggest that (i) gene flow will be a minor contributor to product admixture and (ii) a tolerance level of 0% transgenic wheat in nontransgenic wheat grain, as currently demanded by some groups of producers and consumers, is unrealistic. Tolerance levels, probably ranging from 1 to 5%, will have to be established on the basis of the impurities arising from various transgene contributors such as breeder and certified seed purity, gene flow from neighboring fields, crop volunteers, occurrence of gene introgression from related or weedy interspecific hybrids, mechanical admixture, and grain handling.
Table 1. Meteorological data ([+ or -] SD) for the estimated
pollination period between Purendo-38 and CDC Teal and AC
Navigator in 2000 and 2001.

                         Prevailing
Day       Cultivar          wind        Wind speed       Temperature

                                      km [h.sup.-1]      [degrees]C

                               2000

11 July   CDC Teal        W           15 [+ or -] 6    18 [+ or -] 3
12 July   CDC Teal/AC
            Navigator     W           13 [+ or -] 6    19 [+ or -] 5
13 July   CDC Teal/AC
            Navigator     E           13 [+ or -] 6    22 [+ or -] 6
14 July   CDC Teal/AC
            Navigator     SE          21 [+ or -] 15   24 [+ or -] 5
15 July   CDC Teal/AC
            Navigator     WNW         26 [+ or -] 12   17 [+ or -] 2
16 July   CDC Teal/AC
            Navigator     WNW         23 [+ or -] 6    15 [+ or -] 3
17 July   CDC Teal/AC
            Navigator     ESE         22 [+ or -] 7    12 [+ or -] 4
18 July   CDC Teal/AC
            Navigator     NE          13 [+ or -] 5    13 [+ or -] 1
19 July   CDC Teal/AC
            Navigator     E            9 [+ or -] 3    13 [+ or -] 4
20 July   AC Navigator    ESE         11 [+ or -] 3    15 [+ or -] 4
21 July   AC Navigator    SE           9 [+ or -] 5    18 [+ or -] 5
22 July   AC Navigator    W            5 [+ or -] 3    22 [+ or -] 6

                               2001

5 July    CDC Teal        SSE & S     27 [+ or -] 6    25 [+ or -] 6
6 July    CDC Teal        W           24 [+ or -] 11   20 [+ or -] 6
7 July    CDC Teal/AC
            Navigator     W           14 [+ or -] 7    21 [+ or -] 7
8 July    CDC Teal/AC
            Navigator     NE          11 [+ or -] 4    23 [+ or -] 5
9 July    CDC Teal/AC
            Navigator     N           12 [+ or -] 5    21 [+ or -] 7
10 July   CDC Teal/AC
            Navigator     SSE         18 [+ or -] 7    23 [+ or -] 5
11 July   CDC Teal/AC
            Navigator     SSE         20 [+ or -] 9    21 [+ or -] 3
12 July   CDC Teal/AC
            Navigator     NE & ENE    14 [+ or -] 5    20 [+ or -] 3
13 July   CDC Teal/AC
            Navigator     NE          12 [+ or -] 5    19 [+ or -] 6

                             Relative
                           humidity (%)

                                                 Total
Day       Cultivar       Maximum   Minimum   precipitation

                                                  mm

                          2000

11 July   CDC Teal          99       60            0
12 July   CDC Teal/AC
            Navigator       99       46            0
13 July   CDC Teal/AC
            Navigator       94       43            0
14 July   CDC Teal/AC
            Navigator       82       35            3.5
15 July   CDC Teal/AC
            Navigator       96       61            0.5
16 July   CDC Teal/AC
            Navigator       92       61            0
17 July   CDC Teal/AC
            Navigator       95       47            4.5
18 July   CDC Teal/AC
            Navigator       98       80            0.2
19 July   CDC Teal/AC
            Navigator      100       61            0
20 July   AC Navigator      95       51            0
21 July   AC Navigator      90       55            0.5
22 July   AC Navigator     100       40            0

                          2001

5 July    CDC Teal          70       23            0
6 July    CDC Teal          77       27            0
7 July    CDC Teal/AC
            Navigator       88       28            0
8 July    CDC Teal/AC
            Navigator       82       34            0
9 July    CDC Teal/AC
            Navigator      100       26            0
10 July   CDC Teal/AC
            Navigator       82       30            0
11 July   CDC Teal/AC
            Navigator       94       60            0
12 July   CDC Teal/AC
            Navigator      100       62            0.3
13 July   CDC Teal/AC
            Navigator      100       39            0

Table 2. Confirmed and unconfirmed (in parentheses) percent gene
flow rates for CDC Teal at various distances and directions from
a blue-grained pollinator grown at Saskatoon, SK, in 2000 and 2001.

Distance from
pollinator (m)           North          NE           East

                               2000

0.2                   0.30 (0.63)   0.10 (0.15)   0.08 (0.15)
1                     0.30 (0.49)      0 (0.05)   0.21 (0.29)
5                     0.06 (0.09)      0 (0)      0.01 (0.03)
10                    0.16 (0.21)   0.03 (0.03)      0 (0)
20                       0 (0)      0.01 (0.01)   0.01 (0.01)
40                       0 (0.03)      0 (0)      0.01 (0.01)
60                       0 (0)         0 (0)         0 (0)
80                       0 (0)         0 (0)         0 (0)
100                   0.01 (0.01)      0 (0)         0 (0)
120                      0 (0)         0 (0)         0 (0)
140                      0 (0)         0 (0)         0 (0)
160                      0 (0)         0 (0)         0 (0)
Average (0.2-100 m)   0.09          0.02          0.04

                               2001

0.2                   0.13 (0.13)   0.03 (0.03)   0.24 (0.28)
1                     0.05 (0.10)   0.04 (0.04)   0.15 (0.18)
5                     0.03 (0.06)   0.03 (0.03)   0.08 (0.10)
10                       0 (0)         0 (0)      0.10 (0.13)
20                       0 (0.01)      0 (0)      0.05 (0.08)
40                       0 (0.01)      0 (0)      0.01 (0.01)
60                       0 (0.01)      0 (0)         0 (0)
80                       0 (0)         0 (0)      0.01 (0.01)
100                      0 (0)         0 (0)         0 (0)
120                      0 (0)         0 (0)         0 (0)
140                      0 (0)         0 (0)         0 (0)
160                      0 (0)         0 (0)         0 (0)
Average (0.2-100 m)   0.02          0.01          0.07

Distance from
pollinator (m)             SE           South           SW

                               2000

0.2                   0.09 (0.13)    0.15 (0.30)    0.10 (0.20)
1                        0 (0.01)    0.04 (0.04)       0 (0.01)
5                        0 (0)       0.01 (0.01)       0 (0)
10                       0 (0)          0 (0)          0 (0)
20                    0.03 (0.03)       0 (0)          0 (0)
40                       0 (0.01)    0.01 (0.03)       0 (0.03)
60                       0 (0)          0 (0.03)       0 (0)
80                       0 (0)          0 (0)          0 (0)
100                      0 (0.01)       0 (0)          0 (0)
120                      0 (0)          0 (0)          0 (0)
140                      0 (0)          0 (0)          0 (0)
160                      0 (0)          0 (0)          0 (0)
Average (0.2-100 m)   0.01           0.02           0.01

                               2001

0.2                   0.01 (0.05)    0.01 (0.08)    0.03 (0.03)
1                     0.01 (0.01)    0.03 (0.03)       0 (0.03)
5                     0.01 (0.08)       0 (0.01)    0.01 (0.06)
10                    0.03 (0.05)       0 (0.01)       0 (0.01)
20                    0.03 (0.03)       0 (0.05)       0 (0)
40                    0.03 (0.04)       0 (0)          0 (0)
60                       0 (0)          0 (0)          0 (0)
80                       0 (0)          0 (0)          0 (0)
100                      0 (0)          0 (0)          0 (0)
120                      0 (0)          0 (0)          0 (0)
140                      0 (0)          0 (0)          0 (0)
160                      0 (0)          0 (0)          0 (0)
Average (0.2-100 m)   0.01          0.004          0.004

Distance from
pollinator (m)           West           NW        Average

                             2000

0.2                   0.34 (0.61)   0.41 (0.63)    0.20
1                     0.44 (0.73)   0.38 (0.69)    0.17
5                     0.15 (0.16)   0.04 (0.09)    0.04
10                    0.04 (0.06)   0.13 (0.16)    0.04
20                    0.01 (0.01)   0.04 (0.06)    0.01
40                       0 (0)      0.03 (0.04)    0.01
60                       0 (0)      0.01 (0.14)    0.002
80                       0 (0)      0.01 (0.01)    0.002
100                      0 (0)      0.01 (0.01)    0.003
120                      0 (0)         0 (0)       0
140                      0 (0)         0 (0)       0
160                      0 (0)         0 (0)       0
Average (0.2-100 m)   0.11          0.12

                             2001

0.2                   0.11 (0.15)   0.09 (0.13)    0.08
1                     0.13 (0.23)   0.06 (0.09)    0.06
5                     0.01 (0.03)   0.01 (0.03)    0.02
10                    0.04 (0.05)   0.03 (0.03)    0.02
20                       0 (0)         0 (0.03)    0.01
40                       0 (0.03)      0 (0.03)    0.01
60                       0 (0)         0 (0.01)    0
80                       0 (0.04)      0 (0)       0.002
100                      0 (0.04)      0 (0)       0
120                      0 (0)         0 (0)       0
140                      0 (0.04)      0 (0.01)    0
160                      0 (0)         0 (0)       0
Average (0.2-100 m)   0.03          0.02

Table 3. Confirmed and unconfirmed (in parentheses) percent gene
flow rates for AC Navigator at various distances and directions
from a blue-grained pollinator grown at Saskatoon, SK, in 2000
and 2001.

Distance from
pollinator (m)          North           NE           East

                                2000

0.2                  0.11 (0.89)   0.04 (0.26)    0.05 (0.35)
1                    0.19 (0.93)      0 (0.11)    0.06 (0.20)
5                    0.05 (0.36)      0 (0.13)    0.01 (0.23)
10                   0.03 (0.23)      0 (0.15)       0 (0.10)
21                   0.01 (0.05)      0 (0.04)       0 (0.05)
40                      0 (0.08)      0 (0.05)       0 (0.04)
60                      0 (0.05)      0 (0.03)       0 (0.03)
80                      0 (0.03)      0 (0.06)       0 (0)
100                     0 (0)         0 (0)          0 (0.03)
120                     0 (0.04)      0 (0.01)       0 (0)
140                     0 (0)         0 (0)          0 (0.01)
160                     0 (0.04)      0 (0.01)       0 (0)
180                     0 (0)         0 (0)          0 (0.01)
200                     0 (0)         0 (0.01)       0 (0.01)
220                     0 (0.01)      0 (0.08)       0 (0)
240                     0 (0.05)      0 (0.01)       0 (0.05)
260                     0 (0.03)      0 (0.01)       0 (0.05)
Average (0.2-20 m)   0.08          0.01           0.03

                                2001

0.2                  0.10 (0.25)   0.05 (0.05)       0 (0)
1                    0.11 (0.25)   0.01 (0.04)       0 (0.01)
5                       0 (0)      0.01 (0.01)    0.01 (0.06)
10                      0 (0)         0 (0)          0 (0.01)
20                      0 (0)         0 (0)          0 (0.01)
40                      0 (0)         0 (0)          0 (0)
60                      0 (0)         0 (0)          0 (0)
80                      0 (0)         0 (0)          0 (0)
100                     0 (0)         0 (0)          0 (0)
120                     0 (0)         0 (0)          0 (0)
140                     0 (0)         0 (0)          0 (0)
160                     0 (0)         0 (0)          0 (0)
180                     0 (0)         0 (0)          0 (0)
200                     0 (0)         0 (0)          0 (0)
220                     0 (0)         0 (0)          0 (0)
240                     0 (0)         0 (0)          0 (0)
260                     0 (0)         0 (0)          0 (0)
Average (0.2-20 m)   0.04          0.02          0.003

Distance from
pollinator (m)           SE           South          SW

                              2000

0.2                  0.01 (0.31)   0.11 (0.43)   0.04 (0.23)
1                       0 (0.05)   0.04 (0.21)      0 (0.06)
5                    0.03 (0.15)      0 (0.15)      0 (0.08)
10                   0.01 (0.05)   0.01 (0.10)      0 (0.01)
21                   0.05 (0.19)      0 (0.05)      0 (0.06)
40                      0 (0.05)      0 (0.01)      0 (0.01)
60                      0 (0.08)      0 (0)         0 (0)
80                      0 (0.06)      0 (0.03)      0 (0.05)
100                     0 (0)         0 (0)         0 (0)
120                     0 (0.01)      0 (0.04)      0 (0.01)
140                     0 (0.03)      0 (0)         0 (0.03)
160                     0 (0.01)      0 (0)         0 (0.04)
180                     0 (0.05)      0 (0.03)      0 (0)
200                     0 (0.05)      0 (0)         0 (0)
220                     0 (0)         0 (0)         0 (0)
240                     0 (0.03)      0 (0)         0 (0)
260                     0 (0.01)      0 (0)         0 (0)
Average (0.2-20 m)   0.02          0.03          0.01

                              2001

0.2                  0.05 (0.05)   0.04 (0.06)   0.06 (0.13)
1                    0.01 (0.03)      0 (0)      0.03 (0.03)
5                       0 (0.01)      0 (0.03)      0 (0)
10                      0 (0.03)      0 (0)         0 (0.01)
20                      0 (0.01)      0 (0)         0 (0)
40                      0 (0.04)      0 (0)         0 (0)
60                      0 (0)         0 (0)         0 (0)
80                      0 (0)         0 (0)         0 (0)
100                     0 (0)         0 (0)         0 (0)
120                     0 (0)         0 (0)         0 (0)
140                     0 (0)         0 (0)         0 (0.01)
160                     0 (0)         0 (0)         0 (0)
180                     0 (0)         0 (0)         0 (0)
200                     0 (0)         0 (0)         0 (0)
220                     0 (0)         0 (0)         0 (0.01)
240                     0 (0)         0 (0)         0 (0)
260                     0 (0)         0 (0)         0 (0)
Average (0.2-20 m)   0.01          0.01          0.02

Distance from
pollinator (m)           West          NW        Average

                             2000

0.2                  0.14 (0.64)   0.10 (0.71)    0.08
1                    0.03 (0.24)   0.04 (0.29)    0.04
5                    0.05 (0.16)   0.05 (0.16)    0.02
10                   0.04 (0.10)   0.06 (0.24)    0.02
21                      0 (0.10)      0 (0.06)    0.01
40                      0 (0.14)      0 (0.09)    0
60                      0 (0.15)      0 (0.08)    0
80                      0 (0)         0 (0)       0
100                     0 (0)         0 (0.05)    0
120                     0 (0.08)      0 (0.01)    0
140                     0 (0)         0 (0.03)    0
160                     0 (0.05)      0 (0.01)    0
180                     0 (0.04)      0 (0.01)    0
200                     0 (0)         0 (0.04)    0
220                     0 (0)         0 (0)       0
240                     0 (0)         0 (0.05)    0
260                     0 (0)         0 (0)       0
Average (0.2-20 m)   0.05          0.05

                             2001

0.2                  0.08 (0.13)   0.04 (0.08)    0.05
1                    0.04 (0.06)   0.04 (0.04)    0.03
5                       0 (0)      0.01 (0.04)    0.01
10                      0 (0.01)      0 (0)       0
20                      0 (0)      0.01 (0.01)    0.002
40                      0 (0)         0 (0.03)    0
60                      0 (0.01)      0 (0)       0
80                      0 (0)         0 (0.03)    0
100                     0 (0)         0 (0)       0
120                     0 (0.01)      0 (0)       0
140                     0 (0)         0 (0)       0
160                     0 (0)         0 (0.01)    0
180                     0 (0)         0 (0)       0
200                     0 (0)         0 (0)       0
220                     0 (0)         0 (0)       0
240                     0 (0)         0 (0)       0
260                     0 (0)         0 (0)       0
Average (0.2-20 m)   0.02          0.02

Table 4. Unconfirmed and confirmed percent gene flow rates for CDC
Teal and AC Navigator at various distances (180 to 2760 m) and
directions from two blue-grained pollinator sources grown at
Saskatoon, SK, in 2000 and 2001.

                                                    No. of
                                                   putative    No. of
           Pollinator    Distance     Direction     light      total
            source      from polli-      from        blue      seeds
Genotype   ([dagger])    nator (m)    pollinator    seeds     screened

                                   2000

CDC Teal      One           220           NE          0        22 507
                            260           SE          0        16 613
                            260           SW          0        15 234
                            300           W           4        20 557
                            300           NW          1        18 983
                            450           SW          0        18 996
                            550           SW          0        19 782
                            560           W           0        21 475
                            590           NW          4        21 917
                            630           SW          0        15 596
                            700           SW          0        17 066
                            820           W           0        19 272
                            820           NW          0        12 831
                            840           SW          0        17 138
                            980           W           0        17 616
                            990           NW          0        14 454
                           1000           SW          0        18 025
                           1060           SW          0        20 678
                           1200           SW          0        19 118
                           1210           SW          1        27 825
                           1380           SW          0        17 731
                           1420           SW          0        17 881
              Two           670           NW          2        12 934
                            790           NW          0        13 983
                            890           NW          0        20 762
                           1010           NW          0        13 740
                           1030           NW          1        13 873
                           1100           NW          0        19 141
                           1130           NW          1        17 077
                           1290           NW          0        24 940
                           1440           NW          0        15 826
                           1590           NW          0        22 099
                           1640           NW          0        15 823
                           2110           NW          0        24 191
AC Navi-      Two           340           SW          0        12 791
  gator                     480           NE          0        13 220
                            510           NW          4        13 384
                            580           SE          1        15 852

                                   2001

CDC Teal      One           180           N           0        20 328
                            210           NE          0        22 405
                            230           W           0        17 925
                            240           NW          0        19 671
                            260           SW          1        21 588
                            280           NW          0        17 513
                            300           SE          0        22 467
                            320           SW          0        20 843
                            330           NE          0        21 951
                            460           SE          0        22 411
                            580           E           0        25 199
                            590           NE          0        18 610
                            590           NE          0        20 599
                            610           SW          0        23 430
                            640           SE          0        23 324
                            710           SE          0        24 478
                            750           SW          0        18 405
                            760           SW          6        20 623
                            850           SE          0        24 459
                            880           SW          0        26 433
                           1100           SW          0        25 829
                           1210           SW          0        21 954
              Two           970           NW          0        16 816
                           1110           NW          0        11 693
                           1230           NW          0        14 376
                           1260           NW          0        13 993
                           1430           NW          0        17 172
                           1510           NW          0        18 761
                           1540           NW          0        14 020
                           1610           NW          0        19 767
                           2030           NW          0        19 896
                           2360           NW          0        21 244
                           2760           NW          0        30 931
AC Navi-      Two           420           NW          0        13 025
  gator                     420           NE          0        13 920
                            490           SE          0        15 576
                            510           SW          0        12 855
                           1110           NW          0        12 448
                           1280           NW          0        11 485

           Pollinator    Distance     Unconfirmed   Confirmed
            source      from polli-    gene flow    gene flow
Genotype   ([dagger])    nator (m)     rate (%)     rate (%)

                               2000

CDC Teal      One           220          0            0
                            260          0            0
                            260          0            0
                            300          0.02         0
                            300          0.01         0.005
                            450          0            0
                            550          0            0
                            560          0            0
                            590          0.02         0
                            630          0            0
                            700          0            0
                            820          0            0
                            820          0            0
                            840          0            0
                            980          0            0
                            990          0            0
                           1000          0            0
                           1060          0            0
                           1200          0            0
                           1210          0.004        0
                           1380          0            0
                           1420          0            0
              Two           670          0.02         0
                            790          0            0
                            890          0            0
                           1010          0            0
                           1030          0.01         0
                           1100          0            0
                           1130          0.01         0
                           1290          0            0
                           1440          0            0
                           1590          0            0
                           1640          0            0
                           2110          0            0
AC Navi-      Two           340          0            0
  gator                     480          0            0
                            510          0.03         0
                            580          0.01         0

                               2001

CDC Teal      One           180          0            0
                            210          0            0
                            230          0            0
                            240          0            0
                            260          0.004        0
                            280          0            0
                            300          0            0
                            320          0            0
                            330          0            0
                            460          0            0
                            580          0            0
                            590          0            0
                            590          0            0
                            610          0            0
                            640          0            0
                            710          0            0
                            750          0            0
                            760          0.03         0
                            850          0            0
                            880          0            0
                           1100          0            0
                           1210          0            0
              Two           970          0            0
                           1110          0            0
                           1230          0            0
                           1260          0            0
                           1430          0            0
                           1510          0            0
                           1540          0            0
                           1610          0            0
                           2030          0            0
                           2360          0            0
                           2760          0            0
AC Navi-      Two           420          0            0
  gator                     420          0            0
                            490          0            0
                            510          0            0
                           1110          0            0
                           1280          0            0

([dagger]) Pollinator source one = central 50 x 50-m blue-grained
pollinator block surrounded by the 400 x 400-m experimental field
of CDC Teal; Pollinator source two = central 50 x 50-m blue-grained
pollinator block surrounded by the 600 x 600-m experimental field
of AC Navigator.


ACKNOWLEDGMENTS

Appreciation is expressed to the staff of the Crop Development Center, including L. Ehman, G. Trowell, E. Epp, and P. Bulka for their technical assistance throughout the research. This research was funded by a grant from the Monsanto Company (St. Louis, MO).

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M. A. Matus-Cadiz, P. Huel, * M. J. Horak, and L. K. Blomquist

M.A. Matus-Cadiz, P. Hucl, and L.K. Blomquist, Department of Plant Sciences and Crop Development Centre, University of Saskatchewan, 51 Campus Dr., Saskatoon, SK, Canada S7N 5A8; M.J. Horak, Ecological Technology Center, Monsanto Co., 800 North Lindbergh Blvd, St. Louis, MO 63141, USA. Received 14 Mar. 2003. * Corresponding author (hucl@sask.usask.ca).
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Title Annotation:Crop Breeding, Genetics & Cytology
Author:Matus-Cadiz, M.A.; Hucl, P.; Horak, M.J.; Blomquist, L.K.
Publication:Crop Science
Date:May 1, 2004
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