L. and Gossypium barbadense
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- 8.6 Weed risk assessment of cotton
- Section 9 Potential for Vertical Gene Transfer
- 9.1 Intraspecific crossing
8.5 Control measuresThe control of cotton volunteers is important both in cotton fields and outside the fields in areas such as roadsides and drains. There are three types of cotton volunteers that need to be controlled: seedling cotton, established cotton, and regrowth or ‘ratoon’ cotton. Herbicides can be used to control seedling cotton volunteers. Glyphosate has been the most common herbicide used to control these volunteers but, with the uptake of Roundup Ready® and Roundup Ready Flex® GM G. hirsutum, alternative herbicides are being used, including glufosinate ammonium. However, the use of glufosinate ammonium is limited on G. hirsutum volunteers as its effectiveness on G. hirsutum seedlings at the 4 and 8 leaf stage offers incomplete control. Also the commercial release of LibertyLink® G. hirsutum in 2006 means that glufosinate ammonium tolerant G. hirsutum is now available. Other herbicides such as bromoxynil, carfentrazone and a combination of paraquat and diquat have been shown to be effective (Roberts et al. 2002). Cultivation is also a very effective method to control seedling cotton volunteers (Australian Cotton Cooperative Research Centre 2002c). Established or ratoon cotton plants, whether GM or non-GM, are difficult to control by herbicides alone. Instead, established or ratoon cotton plants are most effectively controlled by mechanical methods involving mulching, root cutting and cultivation (Roberts et al. 2002). Cotton volunteers are actively managed on-farm by mechanical methods involving mulching, root cutting and cultivation (using cultivators, graders, excavators or chippers), application of herbicides (if in the seedling stage) or burning (Australian Cotton Cooperative Research Centre 2002c; Charles et al. 2002; Roberts et al. 2002). A range of herbicides may be used to control cotton volunteers (at the seedling stage) that emerge after harvest. Herbicides containing carfentrazone-ethyl or paraquat and diquat as active constituents are currently registered by the APVMA for control of volunteer cotton, including Roundup Ready® G. hirsutum volunteers (APVMA Pubcris database). Integrated weed management strategies stress the need to avoid relying on one control method (Roberts & Charles 2002). To avoid development of glyphosate resistant weeds for example, it is recommended that the application of glyphosate alone should not be used as the sole management strategy.
In summary, as a volunteer (rather than as a crop), cotton is considered to:
This is consistent with previous assessments of cotton in Australia described in Section 8.2, and provides a baseline for the assessment of GM cotton. Section 9 Potential for Vertical Gene TransferThe possibility of genes transferring from G. hirsutum to other cultivated cotton species, including feral populations, and native Australian Gossypium species organisms is addressed below. There are two potential barriers which must be overcome before gene flow can occur successfully. Pre-zygotic barriers include geographic separation, differences in floral phenology, different pollen vectors and different mating systems such as stigmatic or stylar incompatibility systems. Post-zygotic barriers include genetic incompatibility at meiosis, selective abortion, lack of hybrid fitness and sterile or unfit backcross progeny (Brown et al. 1997). 9.1 Intraspecific crossingCotton is generally self-pollinating, however cross-pollination can occur (see Section 4). In Australia, cross-pollination between adjacent individuals occurs, albeit at relatively low frequencies. For example, as noted in Section 4.2, Llewellyn and Fitt (Llewellyn & Fitt 1996) estimated that cross-pollination between G. hirsutum plants in adjacent rows accounted for only 1 to 2% of seeds. Crossing between cultivated cotton and feral cotton populations is also possible and viable seeds would be generated if it occurred. The likelihood of this occurring is remote, however, given the geographic separation of feral cotton populations from existing cotton plantations (see Section 8). Geographic distances between these feral populations and most cotton growing regions exceeds conceivable pollinator foraging ranges and therefore serves as an effective natural barrier to cross-pollination. However, certain potential cotton growing areas in the NT, particularly areas in the Roper and Sturt Plateau regions, may occur in relatively close proximity to some feral cotton populations. In these areas, there is an increased probability of out-crossing to feral cotton populations. Directory: internet internet -> Applications and limitations internet -> Natural Resources Conservation Service Conservation Practice Standard internet -> Practice Exercise Created By Stavros Charalambous The Internet internet -> It’s a good Topic internet -> National Preventative Health Strategy – the roadmap for action internet -> Downloading gps gr-3 Surveys Summary of Procedure internet -> 3G300m-how to setup the 3g router Mode? Product line: 3g question categories: Function configurations Note internet -> Installation Work has never been simpler or easier internet -> All applications must be submitted by 12/01/2015 to be eligible Download 0.64 Mb. Share with your friends:
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