The biology and ecology of hexaploid wheat (Triticum aestivum L.) and its implications for trait confinement

Abstract

Willenborg, C. J. and Van Acker, R. C. 2008. The biology and ecology of hexaploid wheat (Triticum aestivum L.) and its implications for trait confinement. Can. J. Plant Sci. 88: 997Á1013. This review summarizes the biological and ecological factors of hexaploid wheat (Triticum aestivum L.) that contribute to trait movement including the ability to volunteer, germination and establishment characteristics, breeding system, pollen movement, and hybridization potential. Although wheat has a short-lived seedbank with a wide range of temperature and moisture requirements for germination and no evidence of secondary dormancy, volunteer wheat populations are increasing in relative abundance and some level of seed persistence in the soil has been observed. Hexaploid wheat is predominantly self-pollinating with cleistogamous flowers and pollen viability under optimal conditions of only 0.5 h, yet observations indicate that pollen-mediated gene flow can and will occur at distances up to 3 km and is highly dependent on prevailing wind patterns. Hybridization with wild relatives such as A. cylindrica Host., Secale cereale L., and Triticum turgidum L. is a serious concern in regions where these species grow in field margins and unmanaged lands, regardless of which genome the transgene is located on. More research is needed to determine the long-term population dynamics of volunteer wheat populations before conclusions can be drawn with regard to their role in trait movement. Seed movement has the potential to create adventitious presence (AP) on a larger scale than pollen, and studies tracing the movement of wheat seed in the grain handling system are needed. Finally, the development of mechanistic models that predict landscape-level trait movement are required to identify transgene escape routes and critical points for gene containment in various cropping systems. ) qui concourent au flux de certains caracte`res, dont la repousse spontane´e, la germination et les parame`tres de l'implantation, le syste`me de reproduction, le de´placement du pollen et le potentiel d'hybridation. Bien que les semences du ble´n'aient pas une grande longe´vite´et que leur germination soit lie´e a`maintes contraintes thermiques et hydriques, sans e´vidence de dormance secondaire, les peuplements a`re´ge´ne´ration naturelle sont de plus en plus nombreux et on note une certaine persistance des semences dans le sol. Le ble´hexaploı¨de est essentiellement autogame; ses fleurs sont cle´istogames et, dans les conditions optimales, le pollen n'est viable que 0,5 h. Pourtant, des observations indiquent que le pollen est responsable d'un flux ge´ne´tique jusqu'a`une distance de 3 km, mais que le phe´nome`ne de´pend fortement de la direction des vents dominants. L'hybridation avec des espe`ces sauvages apparente´es telles A. cylindrica Host., Secale cereale L. et Triticum turgidum L. est tre`s pre´occupante dans les re´gions ou`ces espe`ces poussent a`la lisie`re des champs et dans les terres incultes, peu importe le ge´nome portant le transge`ne. Il faudr...

Outcrossing in Early‐Stage Spring Wheat Breeder Seed Development

“…The biological and regulatory implications of gene fl ow in wheat have been the subject of a number of recent literature reviews (Waines and Hegde, 2003;Gaines et al, 2007a;Willenborg and Van Acker, 2008. The biological and regulatory implications of gene fl ow in wheat have been the subject of a number of recent literature reviews (Waines and Hegde, 2003;Gaines et al, 2007a;Willenborg and Van Acker, 2008.…”

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O utcrossing (OC) in wheat and the potential for gene fl ow have received increased attention in the last decade with transgenic traits approaching commercialization. The biological and regulatory implications of gene fl ow in wheat have been the subject of a number of recent literature reviews (Waines and Hegde, 2003;Gaines et al, 2007a;Willenborg and Van Acker, 2008. ) To date research in wheat has focused on genotypic diff erences in OC (Hucl, 1996) and the level of OC over a range of distances and fi eld scales representing experimental small plot work (Hucl and Matus-Cádiz, 2001), breeder seed plots (Matus-Cádiz et al, 2004; Hanson et al, 2005), and commercial production (Matus-Cádiz et al, 2007).

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Crop Genotype and Plant Population Density Impact Flowering Phenology and Synchrony between Cropped and Volunteer Spring Wheat

“…However, there are ecological and agricultural concerns associated with the cultivation of transgenic crops. Of particular importance with regard to risk assessment and property rights protection is the migration of transgenes to the same species (intraspecific gene flow), including neighboring nontransgenic crops and volunteer crop plants (Ellstrand, 2003; Gruber et al, 2007; Willenborg and Van Acker, 2008).…”

“…A recent report indicates that transgenic wheat is already being field‐tested in Australia (Finkel, 2008). Cultivar purity should be relatively simple and easy to maintain in wheat because it is predominantly a self‐fertilizing species (Willenborg and Van Acker, 2008). However, because its mating system allows for partial intermating (<1%), off‐types attributable to outcrossing are consistently identified (Prakash and Singhal, 2003; Hucl et al, 2004).…”

“…By employing a variety of crop characteristics such as varied planting dates, growth habits, fertility requirements, and herbicide requirements, crop rotations may be an effective strategy for managing volunteer wheat, where persistence tends to be limited to 2 yr (Harker et al, 2005). However, volunteer wheat persistence of up to 5 yr has been recorded (Beckie, 2001) and the high frequency of wheat in the crop rotation may not provide the level of control necessary to prevent trait movement (Leeson et al, 2005; Willenborg and Van Acker, 2008). Monocultures of continuous wheat, wheat‐fallow‐wheat‐fallow, or wheat‐wheat‐fallow are common to Northern Great Plains rotations (Gan et al, 2003; Zentner et al, 2002) and as a result, volunteer wheat is a common weed that is increasing in frequency in western Canada (Leeson et al, 2005).…”