Contents - Faperta

412 Biotechnological Approaches for Pest Management and Ecological Sustainability
related species (Amand, Skinner, and Peaden, 2000). The measurement of the risk of inadvertent
dispersal of transgenes must include the assessment of accidental dispersion of
pollen. Factors to be considered include the rate of pollen spread, the maximal dispersion
distance of pollen, and the spatial dynamics of pollen movement within seed production
fi elds, none of which are known for insect-pollinated crop species.
Assessment of realistic risk for gene transfer through pollen is available for many crops
(Raybould and Gray, 1993), and agriculturally sound procedures need to be developed for
different regions (Boulter, 1995). Evidence of gene fl ow has been reported in sugarbeets
(Desplanque et al., 1999; Bartsch et al., 1999, 2003; Arnaud et al., 2003), cassava (Nassar,
2002), rice (Song et al., 2003; Chen et al., 2004), Brassica (Chevre et al., 1997), sunfl ower (Arias
and Rieseberg, 1994; Linder et al., 1998), and sorghum (Paterson et al., 1995; Arriola and
Ellstrand, 1996, 1997). Crop to weed gene fl ow has been implicated in the evolution of
enhanced weediness in wild relatives of wheat, rye, rice, soybean, sorghum, millet, beans,
and sunfl ower, and extinction of wild relatives in rice and cotton (Sun and Corke, 1992;
Ellstrand, Prentice, and Hancock, 1999). Information on pollen dispersals and gene fl ow in
different crops is discussed below.
Cotton
In cotton, pollen dispersal increases with an increase in the size of the source plot (Llewellyn
and Fitt, 1996). A buffer zone of 20 m would limit the dispersal of transgenic pollen from
small-scale fi eld tests. In China, the potential for gene introgression from Bt cotton lines
into wild or cultivated sexually compatible plants is very low, and such events are highly
unlikely to increase the weediness potential of any resulting progeny. There is no pollen
transfer between Gossypium hirsuturm L. and G. arboreum L. although these species have
been grown together in India for several decades (Figure 13.1).
Cereals
In rice, pollination of recipient plants with pollen of the transgenic plant occurs at a signifi
cant frequency (Messeguer et al., 2001). A gene fl ow slightly lower than 0.1% has been
detected in a normal side-by-side plot design. Similar results have been obtained in a
FIGURE 13.1 There are several barriers for gene fl ow and survival of interspecifi c hybrids. No intermediates
have been observed between cultivated Gossypium hirsutum and Gossypium arboreum cottons under natural
conditions.