The introduction of transgenic crops can bring benefits for farmers and the environment but raises three main reasons of concern: (1) genetic flow from genetically modified (GM) crops to conventional crops in nearby fields, through pollination; (2) genetic flow from GM crops to wild relatives (hybridization) and, subsequently, to conventional crops; (3) diffusion of volunteer transgenic plants, i.e. GM plants which emerge within conventional crops, from seeds or propagules set by GM crops grown on the same fields in previous years. Other reasons of concern are mainly related to herbicide resistant GM crops, which may encourage a less efficient use of herbicides, contributing to the spread of resistant weeds and to herbicide residue accumulation in plant tissues and in the environment. The risk of genetic flow is crop-dependent and must be considered and minimised for a safe coexistence of GM and conventional crops. Genetic flow has been studied in detail in corn and canola, the outcrossing crops for which GM varieties are widespread, and recent literature is reviewed in this chapter. There are several ways to reduce the above mentioned problems. Suitable design of genetic constructs, male and female sterility, flowering control, transgene mitigation strategies, chloroplast engineering, are all technologies that can help to reduce or prevent the flow of transgenes and their possible impact on the environment. Agronomic practices play an important role. A first factor is the careful selection of fields, to ensure a good spatial separation between GM and conventional crops and to avoid cross pollination. Distances must be established according to the mating system and the pollen dispersal capacity of each GM crop species of interest. For GM crops, measures have also to be taken to minimize seed shedding before and during harvesting and to ensure an accurate cleaning of harvesting machinery and stocking equipments. Crop rotation is a very important factor to avoid the problem of volunteer plants. Indeed, volunteer GM plants are particularly dangerous if a conventional crop follows strictly a GM crop of the same species. Therefore, the selection of an appropriate rotation cycle is fundamental, according to seed viability and dormancy patterns of the different GM species. Concerning tillage, ploughing is always advisable after a GM crop, to obstacle the germination of GM seeds in the following season. In the case of species with a very prolonged seed viability in soil, ploughing should be carried out about 4-5 weeks after harvesting, to stimulate seed germination before seed burial. On the contrary, in the case of species characterised by a shortly persistent seed-bank, ploughing should be carried out immediately after harvesting. Other agro-technological tools are false-seed bed preparation and the adoption of weed control measures to eliminate volunteer plants, as well as wild relatives of GM crops from field borders.

Le piante geneticamente modificate nell'agricoltura umbra

ONOFRI, Andrea;ROSELLINI, Daniele;TEI, Francesco;VERONESI, Fabio
2006

Abstract

The introduction of transgenic crops can bring benefits for farmers and the environment but raises three main reasons of concern: (1) genetic flow from genetically modified (GM) crops to conventional crops in nearby fields, through pollination; (2) genetic flow from GM crops to wild relatives (hybridization) and, subsequently, to conventional crops; (3) diffusion of volunteer transgenic plants, i.e. GM plants which emerge within conventional crops, from seeds or propagules set by GM crops grown on the same fields in previous years. Other reasons of concern are mainly related to herbicide resistant GM crops, which may encourage a less efficient use of herbicides, contributing to the spread of resistant weeds and to herbicide residue accumulation in plant tissues and in the environment. The risk of genetic flow is crop-dependent and must be considered and minimised for a safe coexistence of GM and conventional crops. Genetic flow has been studied in detail in corn and canola, the outcrossing crops for which GM varieties are widespread, and recent literature is reviewed in this chapter. There are several ways to reduce the above mentioned problems. Suitable design of genetic constructs, male and female sterility, flowering control, transgene mitigation strategies, chloroplast engineering, are all technologies that can help to reduce or prevent the flow of transgenes and their possible impact on the environment. Agronomic practices play an important role. A first factor is the careful selection of fields, to ensure a good spatial separation between GM and conventional crops and to avoid cross pollination. Distances must be established according to the mating system and the pollen dispersal capacity of each GM crop species of interest. For GM crops, measures have also to be taken to minimize seed shedding before and during harvesting and to ensure an accurate cleaning of harvesting machinery and stocking equipments. Crop rotation is a very important factor to avoid the problem of volunteer plants. Indeed, volunteer GM plants are particularly dangerous if a conventional crop follows strictly a GM crop of the same species. Therefore, the selection of an appropriate rotation cycle is fundamental, according to seed viability and dormancy patterns of the different GM species. Concerning tillage, ploughing is always advisable after a GM crop, to obstacle the germination of GM seeds in the following season. In the case of species with a very prolonged seed viability in soil, ploughing should be carried out about 4-5 weeks after harvesting, to stimulate seed germination before seed burial. On the contrary, in the case of species characterised by a shortly persistent seed-bank, ploughing should be carried out immediately after harvesting. Other agro-technological tools are false-seed bed preparation and the adoption of weed control measures to eliminate volunteer plants, as well as wild relatives of GM crops from field borders.
2006
9788887652116
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11391/130629
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