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esistant hybrid populations might increase under herbivore pressure in mixed stands with a
wild population. Weis and Hochberg (2000) demonstrated that the effect of herbivore pressure
on the relative biomass advantage of resistant plants was magnified by plant density. Vacher
et a l. ( 2004) f ound t hat hi gh-density patches of hi ghly d amaged wild pl ants a re t he m ost
vulnerable to Bt-transgene invasion.
According to the tentative regression equations proposed in Fig 1 and Table 2, there is
a p ossibility t hat t he p erformances o f N C p lants d ecreased w ith i ncreasing NC p ercentage.
The lowest v alues appeared in the pure stands o f NC plants. The most i ntense competition
was in the pure stands of NC plants where there were no CP plants. This could be expected, as
more healthy insect-resistant plants have to share the limited resources available in the pot.
Because selection for the plants possessing the transgene would lead to populations consisting
of 100 % insect-resistant plants, our data indicate that the overall reproductive output of the
resistant popul ation w ould be t he s ame a s a s usceptible, i nsect-attacked popul ation. Thus,
when the resistant plants are in the minority, the fitness advantage for insect-resistant hybrids
is obvi ous, but a s t he f requency o f i nsect-resistant h ybrids i ncreases, ne ighbor competition
limits t heir g rowth. T herefore, c hanging t he po pulation f rom s usceptible to in sect-resistant
would not result in different demographic kinetics in resource-limited habitats.
CONCLUSION
In t his s tudy, w e ha ve not s tudied t he f itness of t he f irst h ybrid ge neration a fter t he
interspecific hybridization between B. napus and B. juncea. Experiments on t hat topic show
that transgenes are likely to persist in the wild populations (Di et al., 2009). In turn, we have
simulated the fate of stabilized introgressants having the transgene for insect-resistance within
a B. juncea population. The effect of simulated herbivory and competition on t he vegetative
and reproductive performances of transgenic plants and wild relatives was clear. Our results
showed t hat c lipping l eaves s ignificantly r educed s ilique num bers, f inal bi omass a nd s eed
output of B. juncea. Clipping leaves had an increasingly negative influence on the survival of
CP pl ants a s t he pr oportion of c lipped l eaves i ncreased. H owever, t he d evelopment of N C
plants w as not obvi ously impacted, i rrespective of the pr oportion of c lipped l eaves of C P
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