UNIVERSITE DE BOURGOGNE THÈSE Yongbo LIU - Université de ...

In general, herbivory had a negative effect on plant fitness (Escarre et al. 1999; Rogers
and S iemann 2002) , bu t c ertain s tudies s howed no e ffects be cause of t he c ompensatory
growth (Strauss and Agrawal 1999; Gadd et al. 2001; Hawkes and Sullivan 2001; Boalt and
Lehtila 2007). In addition, as herbivore attack following artificial leaf damage decreased with
increasing i nitial l eaf d amage, p lants i nduced b y early-season herbivory had higher relative
fitness than un-induced plants (Agrawal 1998; 1999). Thus, the effect of herbivory on plant
growth and reproduction is uncommon, and it depends on lots of factors such as plant species
(Rogers and Siemann 2002), resource level (Hawkes and Sullivan 2001; Rogers and Siemann
2002), damage time (Agrawal 1998; 1999), and herbivores (Schooler et al .2006).
A cr op-developed Bacillus t huringiensis (Bt) t ransgene i s one of m ost i mportant
transgenes employed in GM crops, because the insecticidal proteins produced by Bt are toxic
to major pests of many of the world’s most important crops such as cotton, rice, corn, oilseed
rape, and sunflower. The gene flow and introgression from Bt crops to wild relatives is likely
to r esult i n a de crease i n he rbivore da mage, t herein h ybrids pr oduced greater pl ant f itness
(survivor, growth and f ecundity) c ompared w ith a n e quivalent w ild po pulation t hat i s not
protected by Bt based resistance trait (Stewart et al. 1996; Ramachandran et al. 2000; Snow et
al. 2003; V acher e t al. 2004) . M oreover, no f itness c ost of e xpressing Bt-transgene w as
detected in the Brassiceae (Mason et al. 2003; Moon et al. 2007) and in sunflower (Snow et al.
2003), although Vacher et al. (2004) found a lower seed output in Bt hybrids than wild plants
in the absence of herbivores.
However, the plant fitness consequences of insect-resistant Bt-transgene on wild plants
are h erbivores de pendant, a nd m ost s tudies s howed a f itness i ncrease w hen pl ants w ere
protected f rom Bt-susceptible he rbivores. S tewart e t a l. (1996) d emonstrated a s ignificant
increase in biomass and seed yield in transgenic oilseed rape exposed to diamondback moth
larvae compared to nontransgenic plants in field trials. Snow et al. (2003) found 55% more
seed set on male-sterile, transgenic Bt sunflower than for a non-transgenic controls. Moon et
al. (2007) showed significantly higher biomass and seed yield in greenhouse conditions with
herbivore additions, using transgenic Bt wild B. rapa and B. rapa × B. napus hybrids (with
and w ithout t he Bt transgene). H owever, i nsect-resistant tr ait d id n ot r esult in a f itness
increase in the absence of or presence of low herbivory (Ramachandran et al. 2000; Moon et
al. 2007) . S utherland e t a l. ( 2006) f ound t hat s imulated he rbivory (only cotyledons w ere
mechanically damaged) did not have a plant fitness effect for B. napus × B. rapa hybrids and
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