Estimating out-crossing rates in spring wheat cultivars using the contact method.
MATERIALS AND METHODS
Seed of Purendo-38, an awnless, spring type blue-aleuroned wheat was obtained from the Crop Development Center, Saskatoon, SK. The blue-grained trait is a dominant gene marker that has been applied within gene flow studies (Hucl and Matus-Cadiz, 2001; Matus-Cadiz et al., 2004). Certified seed was used for all 35 cultivars tested (Table 1). Of the cultivars tested, 34 were Canadian cultivars including 19 of the Canada Western Red Spring (CWRS) class, seven of the Canada Prairie Spring (CPS) wheat class, four of the Canada Western Extra Strong (CWES) class, and four of the Canada Western Amber Durum (CWAD; Triticum turgidum L.) class. Rongotea, a New Zealand cultivar (Griffin, 1987), was grouped with CPS cultivars for presentation purposes because Rongotea has similar agronomic and quality characteristics when compared to CPS cultivars.
For the 2001 and 2002 greenhouse studies, 20 pots of Purendo-38 were seeded weekly for 5 wk starting on 25 May 2001 and 24 Sept. 2002 to ensure sufficient pollen for crossing. Recipient cultivars (one pot per cultivar) were seeded weekly for 4 wk starting on 28 May 2001 and 27 Sept. 2002 to ensure a sufficient number of spikes for crossing. Different greenhouses were used in each year of the study, with artificial light condition being more favorable in 2002 compared to 2001. In 2001, conditions were set at 24/18[degrees]C (day/night) with 18 h light and a photosynthetically active radiation level of 150 [micro]mol [m.sup.-2] [s.sup.-1]. In 2002, conditions were set at 23/18[degrees]C (day/night) with 18 h light and a photosynthetically active radiation level of 250 [micro]mol [m.sup.-2] [s.sup.-1]. Pots (15-cm diameter) were filled with Terra-Lite Redi-Earth (W.R. Grace and Co. of Canada Ltd., Ajax, ON). Six seeds were planted per pot at a depth of 2.5 cm. Seedlings were watered every 2 d and fertilized at Zadoks growth stage 12 (ZGS 12; Zadoks et al., 1974) once using 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].
When seedlings reached the two-leaf stage (ZGS 12), up to three seedlings were removed from each pot to allow three plants to establish per pot. Under these growing conditions, plants within pots produced an average of five to six tillers. All tillers were used for crossing. Each recipient cultivar was crossed with Purendo-38 by covering up to three non-emasculated spikes of a given cultivar and one Purendo-38 spike as pollen source with an individual glassine bag (5 by 19 cm). The number of recipient spikes in a bag was based on spike availability. Awns were clipped to 1 cm above their respective glume before crossing to allow glassine bags to slip easily over multiple spikes. The bags were removed 7 d after pollination to allow for normal grain development and ripening. Crossed spikes were harvested at ZGS 92 (seeding dates were maintained separate), air-dried at 24[degrees]C (40% relative humidity) for 7 d, and then individually hand threshed.
Cross-pollination events from Purendo-38 to recipient cultivars were identified by the expression of a light-blue pigment in the aleurone layer of putative [F.sub.1] seed. Seeds possessing a light-blue aleurone were visually identified using a fluorescent light box source and separated from the remaining seed lot. Putative light-blue [F.sub.1] seeds were sown in the greenhouse and resulting plants were selfed and grown to maturity to confirm the light-blue [F.sub.1] seed was the result of an out-crossing event. Before planting, the seeds were surface sterilized for 8 min using a 2.5% sodium hypochlorite and 0.1% (v/v) Tween 20 solution, rinsed for 5 min with water, followed by a rinse with 70% ethanol, and then air-dried at room temperature. Seeds were pregerminated in the dark at 15[degrees]C for 10 d in a petri dish (each containing a Whatman No. 1 filter paper) and subsequently transferred to soil. The pregerminated seeds were planted (2.5-cm depth) in 15-cm-diameter pots (three plants per pot) as described above and grown to maturity using the greenhouse conditions described for 2002. Spikes from individual plants were harvested and hand threshed separately. The [F.sub.1]-derived [F.sub.2] seed was classified as segregating (3:1 blue/nonblue seed ratio) or nonsegregating (all nonblue seeds) for the blue-aleurone trait.
Out-crossing rates were calculated for each cultivar as follows: OC (%) = 100(total number of confirmed light-blue seeds observed/total number of seeds collected) where confirmed light-blue seeds included only light-blue [F.sub.1] seeds that segregated for the blue-aleurone trait in greenhouse grow outs. In 2001 and 2002, OC rates were calculated by pooling values across the four seeding dates. Means were tested for significance (P [less than or equal to] 0.05) using one-tailed t tests (Minitab Version 13; Minitab Inc., State College, PA).
RESULTS AND DISCUSSION
This 2-yr greenhouse-based study indicates that OC rates in spring wheat cultivars grown in direct spike contact under greenhouse conditions are generally at levels below 2.8% but can exceed 10% (Table 1). Generally, OC rates were less than 2.8% in 2001 and 2002, with the exception of CPS cv. Genesis (3.5% in 2002), CWES cv. Wildcat (6.3% in 2001; 4.2% in 2002), and CWES cv. Glenlea (10.6% in 2001; 8.6% in 2002). In 2001, OC rates ranged from 0 to 2.8% for CWRS cultivars (mean = 0.6), 0 to 1.5% for CPS cultivars (mean = 0.4), 0 to 10.6% for CWES cultivars (mean = 4.3), and 0 to 0.4% for CWAD cultivars (mean = 0.2). In 2002, OC rates ranged from 0 to 2.0% for CWRS cultivars (mean = 0.7), 0 to 3.5% for CPS cultivars (mean = 1.7), 1.5 to 8.6% for CWES cultivars (mean = 4.1), and 0.2 to 1.4% for CWAD cultivars (mean = 0.5).
Eighteen out of the 35 cultivars tested were prone to OC levels of [greater than or equal to] 1% in at least 1 yr of the study while Rongotea, Glenlea, and Wildcat were prone to OC, with rates of [greater than or equal to] 1% in both years. Out-crossing levels in the CPS class were significantly lower in 2001 (mean = 0.4) compared with 2002 (mean = 1.7) while OC levels in the three other wheat classes were similar in both years. These results suggest that OC rates in wheat are cultivar and greenhouse environment dependent. Twenty of the cultivars tested possessed awns (Table 1). 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), suggesting that their removal before crossing in our study may have promoted higher OC rates than would have been expected had the awns been retained. In contrast, interspecific barriers to hybridization were likely of greater importance in impeding OC rates in the CWAD class.
In wheat, successful OC depends on the receptivity of the stigma, the viability of the pollen, and availability of pollen during the receptive period (Johnson and Schmidt, 1968). These factors vary with genotype and environment (de Vries, 1971, 1972, 1974). Pollen dispersal during flowering varies with environmental factors including prevailing winds, wind speed, temperature, humidity, and precipitation (de Vries, 1971, 1972, 1974). Higher OC rates have been associated with higher wind speeds and prevailing wind directions during the flowering period of a wheat crop (Hucl and Matus-Cadiz, 2001). De Vries (1972) reported that the highest concentration of pollen dispersal occurred at temperatures between 16 and 20[degrees]C and 70 to 75% relative humidity. Daily humidity and temperature, during anthesis were not recorded in the present study and may have been useful in explaining, in part, the higher OC rates in the CPS class in 2002 relative to 2001 (Table 1). Seed production in 2002 was fourfold higher than in 2001. The higher grain production is evidence of more vigorous plant growth, likely a result of the 67% higher photosynthetically active radiation levels and cooler temperatures experienced with the planting in the fall of 2002.
Direct spike contact combined with the four seeding dates used in our current study, unlike the one (Hucl and Matus-Cadiz, 2001) and three (Hucl, 1996) seeding dates in our previous field studies, maximized the level of flowering synchrony between the donor blue-aleuroned pollen source and recipient cultivars. Hucl (1996) reported maximum OC rates for 11 wheat cultivars ranging from 5.2% (Oslo) to 0.2% (Columbus and CDC Makwa) in a field study. In the present greenhouse study, Glenlea (10.6% in 2001; 8.6% in 2002), Wildcat (6.3% in 2001; 4.2% in 2002), and Genesis (0.2% in 2001; 3.5% in 2002) tended to be prone to OC while Oslo tended toward low levels of OC (0.7% in 2001; 1.2% in 2002). In contrast, Hucl (1996) reported that under field conditions Glenlea (0.6%), Wildcat (1.1%), and Genesis (0.3%) tended to be less prone to OC relative to Oslo (5.2%). Similarly, Hucl and Matus-Cadiz (2001) also reported higher OC rates for Oslo under field conditions (3.2%) relative to the rate reported in our current study. Other research has reported that grain yield in Oslo responds differently to moisture stress under controlled environment (Baker, 1996) versus field conditions (Hucl and Graf, 1990), with Oslo showing changes in genotype rank from one environment to another only under field conditions.
Based on this initial research, some cultivars appear to be consistently low out-crossers regardless of environment while others appear to be prone to OC depending on the environment. In both years, the CWES class had the highest mean OC rates of all classes studied (4.3% in 2001; 4.1% in 2002), in large part due to the cultivars Glenlea and Wildcat. Spike laxness appears to result in a greater degree of floret opening in wheat (de Vries, 1971). The CWES cultivars Glenlea and Wildcat have laxer, fusiform spikes and lower pollen stainability relative to other spring wheat cultivars (Hucl, 1996). Hucl (1996) suggested that these morphological traits may, at least in part, explain the proneness of the two cultivars toward OC under field conditions. Out-crossing rates estimated under greenhouse conditions appear to be poor predictors of OC rates under field conditions. Further research is needed to quantify genetic variability for OC and assess the nature of the G X E interaction in determining OC in wheat.
Appreciation is expressed to L. Ehman, M. Grieman, W. Schatz, K. Jackle, A. Overlid, and S. Campbell for their technical assistance.
Abbreviations: CPS, Canada Prairie Spring; CWAD, Canada Western Amber Durum; CWES, Canada Western Extra Strong: CWRS, Canada Western Red Spring; OC, out-crossing.
Baker, R.J. 1996. Oslo and Biggar spring wheats respond differently to controlled temperature and moisture stress. Can. J. Plant Sci. 76:413-416.
Briggs, K.G., O.K. Kiplagat, and A.M. Johnson-Flanagan. 1999. Floret sterility and outcrossing in two spring wheat cultivars. Can. J. Plant Sci. 79:321-328.
de Vries, A. p. 1971. Flowering biology of wheat particularly in view of hybrid seed production: A review. Euphytica 20:152-170.
de Vries, A.P. 1972. Some aspects of cross pollination in wheat (Triticure aestivum L). 1. Pollen concentration in the field as influenced by variety, diurnal pattern, weather conditions, and level as compared to the height of the pollen donor. Euphytica 21:185-203.
de Vries, A.P. 1974. Some aspects of cross pollination in wheat (Triticure aestivum L). 4. Seed set on male sterile plants as influenced by distance from pollen source, pollinator: Male sterile ratio, and width of the male sterile strip. Euphytica 23:601-622.
Griffin, W.B. 1987. Out-crossing in New Zealand wheats measured by occurrence of purple grain. N. Z. J. Agric. Res. 30:287-290.
Hucl, P. 1996. Out-crossing rates for 10 Canadian spring wheat cultivars. Can. J. Plant Sci. 76:423-427.
Hucl, R, and R.J. Graf. 1990. Evidence of cross-over interaction involving four spring wheat cultivars, p. 135-142. In New Frontiers in Prairie Agriculture. Proc. Soils and Crops Workshop. 22-23 Feb. 1990. Univ. of Saskatchewan Ext. Press, Saskatoon, SK.
Hucl, R, and M.A. Matus-Cadiz. 2001. Isolation distances for minimizing out-crossing in spring wheat. Crop Sci. 41:1348-1351.
Johnson, V.A., and J.W. Schmidt. 1968. Hybrid wheat. Adv. Agron. 20:199-232.
Matus-Cadiz, M.A, R Hucl, M.J. Horak, and K. Blomquist. 2004. Gene flow in wheat at the field scale Crop Sci. 44:718-727.
Waines, J.G., and S.G. Hegde. 2003. Intra-specific gene flow in bread wheat as affected by reproductive biology and pollination ecology of wheat flowers. Crop Sci. 43:451-463.
Zadoks, J.C., T.T. Chang, and C.F. Konzak. 1974. A decimal code for the growth stages of cereals. Weed Res. 14:415-421.
R. G. Lawrie, M. A. Matus-Cadiz, and P. Hucl *
Dep. of Plant Sciences and Crop Development Centre, Univ. of Saskatchewan, 51 Campus Dr., Saskatoon, SK, Canada S7N 5A8. Received 20 Apr. 2005. * Corresponding author (email@example.com).
Table 1. Out-crossing rates (%) for cultivars crossed in 2001 and 2002 using the direct spike contact method. Out- crossing Class ([dagger]) Cultivar Awn type 2001 CWRS AC Abbey Awned 0 Laura Awned 0.23 McKenzie Awned 0 Prodigy Awned 0 Superb Awned 0.42 AC Cadillac Awnless 0 AC Cora Awnless 0 AC Domain Awnless 1.25 AC Eatonia Awnless 0 AC Elsa Awnless 0.81 AC Intrepid Awnless 0 AC Majestic Awnless 1.52 AC Splendor Awnless 0 CDC Bounty Awnless 0 CDC Makwa Awnless 2.76 CDC Teal Awnless 0 5600HR Awnless 1.47 Katepwa Awnless 0.94 Roblin Awnless 1.26 Mean ([+ or -] SE) 0.6a (0.2) ([double dagger]) CPS AC Crystal Awned 0 AC Foremost Awned 0.27 AC Karma Awned 0 AC Taber Awned 0.67 Biggar Awned 0 Genesis Awned 0.23 Oslo Awned 0.72 Rongotea Awned 1.48 Mean ([+ or -] SE) 0.4b (0.2) CWES Bluesky Awned 0.45 CDC Rama Awned 0 Wildcat Awned 6.28 Glenlea Awnless 10.63 Mean ([+ or -] SE) 4.3a (2.5) CWAD AC Avonlea Awned 0 AC Navigator Awned 0.42 Plenty Awned 0 Sceptre Awned 0.31 Mean ([+ or -] SE) 0.2a (0.1) Statistics Grand mean 0.9a Standard error ([+ or -] SE) 0.3 Minimum 0 Maximum 10.6 Total Out- number of crossing seeds Class ([dagger]) Cultivar 2002 2001 CWRS AC Abbey 0.22 210 Laura 1.24 437 McKenzie 1.27 281 Prodigy 1.22 278 Superb 1.95 237 AC Cadillac 0 271 AC Cora 0.33 271 AC Domain 0.43 319 AC Eatonia 0.71 284 AC Elsa 0.41 371 AC Intrepid 0.33 149 AC Majestic 0.25 197 AC Splendor 0.19 233 CDC Bounty 0.26 310 CDC Makwa 0.32 326 CDC Teal 1.25 261 5600HR 0.69 614 Katepwa 0.50 213 Roblin 0.98 317 Mean ([+ or -] SE) 0.7a (0.1) 294 (23) CPS AC Crystal 1.51 423 AC Foremost 0.71 369 AC Karma 2.31 283 AC Taber 1.34 299 Biggar 0.68 342 Genesis 3.47 427 Oslo 1.22 279 Rongotea 2.09 338 Mean ([+ or -] SE) 1.7a (0.3) 345 (21) CWES Bluesky 2.11 442 CDC Rama 1.52 212 Wildcat 4.18 223 Glenlea 8.55 348 Mean ([+ or -] SE) 4.1a (1.6) 306 (55) CWAD AC Avonlea 0.26 81 AC Navigator 1.43 238 Plenty 0.33 242 Sceptre 0.15 318 Mean ([+ or -] SE) 0.5a (0.3) 220 (50) Statistics Grand mean 1.3a 298 Standard error ([+ or -] SE) 0.3 16 Minimum 0 81 Maximum 8.6 614 Total number of seeds Class ([dagger]) Cultivar 2002 CWRS AC Abbey 1372 Laura 1527 McKenzie 1577 Prodigy 1316 Superb 1178 AC Cadillac 1103 AC Cora 1215 AC Domain 1163 AC Eatonia 1696 AC Elsa 1224 AC Intrepid 906 AC Majestic 1201 AC Splendor 1034 CDC Bounty 1173 CDC Makwa 1586 CDC Teal 1357 5600HR 1167 Katepwa 1410 Roblin 1325 Mean ([+ or -] SE) 1291 (47) CPS AC Crystal 1523 AC Foremost 987 AC Karma 951 AC Taber 821 Biggar 1326 Genesis 1210 Oslo 1478 Rongotea 764 Mean ([+ or -] SE) 1133 (104) CWES Bluesky 1328 CDC Rama 988 Wildcat 1005 Glenlea 1193 Mean ([+ or -] SE) 1129 (81) CWAD AC Avonlea 1170 AC Navigator 630 Plenty 1204 Sceptre 1291 Mean ([+ or -] SE) 1074 (150) Statistics Grand mean 1211 Standard error ([+ or -] SE) 41 Minimum 630 Maximum 1696 ([dagger]) CWRS, Canada Western Red Spring; CPS, Canada Prairie Spring; CWES, Canada Western Extra Strong; CWAD, Canada Western Amber Durum. ([double dagger]) Means followed by different letters within a row are different at P [less than or equal to] 0.05 using one-tailed t tests.
|Printer friendly Cite/link Email Feedback|
|Author:||Lawrie, R.G.; Matus-Cadiz, M.A.; Hucl, P.|
|Date:||Jan 1, 2006|
|Previous Article:||Outcrossing in annual canarygrass.|
|Next Article:||The 4E-ms system of producing hybrid wheat.|