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

Whether a popul ation w ill e volve t o e quilibrium a lso de pends on t hat p opulation’s
reproductive output and the subsequent plant density of its progeny, which in turn determines
the population d ynamics (Meirmans et al., 2008). Therefore, w e address whether there is a
population maximum seed production for a given percentage of resistant plants under insect
pressure, since resistant plants could benefit from resources that would otherwise have been
consumed b y s usceptible pl ants ( Friess & M aillet, 1997; R odriguez & Brown, 1998 ).
Enhanced seed production could make a population better able to disperse at a cer tain point
during i ts e volution f rom 0 t o 100 % r esistant, m aking i t m ore i nvasive t han t he o riginal
population a nd pot entially m ore t roublesome for e cosystem conservation a nd a griculture.
Conversely, reduced seed production could result in only rare occurrence of insect-resistant
plants.
Oilseed rape (Brassica napus, AACC, 2n=38) is a model crop for transgenic studies,
and Bt-transgenic oilseed rape conferring insect-resistance has been studied for years (Stewart
et al., 1997). Although Ramachandran et al. (2000) found that Bt-transgenic oilseed rape is a
superior c ompetitor c ompared t o non -transgenic oi lseed r ape unde r pr essure from t he
diamondback moth, there are few studies of variation in the competitive interaction when the
frequency o f i nsect-resistant p lants i ncreases. B. j uncea (AABB, 2n= 36), one of t he w ild
relatives of B. napus, is a tetraploid species that is preferentially self-pollinated but that has a
considerable outcrossing rate. It is frequently found as a weed in arable fields and is a ruderal
component of roadsides a nd w aste s ites i n C hina. B. napus and w ild B. j uncea are h ighly
compatible, a nd h ybrids a nd s ubsequent ba ckcross ge nerations ha ve s uccessfully b een
obtained by open pollination (Frello et al., 1995; Bing et al., 1996; Song et al., 2007, Liu et
al., 2010). T he r elatively high c ompatibility raises a bi osafety concern; t ransgene
introgression could occur from transgenic oilseed rape to wild B. juncea. This could then lead
to pe rsistence of t heir hybrids o r ba ckcross p rogeny i n t he w ild B. j uncea habitats a nd,
consequently, t he oc currence of t ransgenic i nsect-resistance w ithin B. j uncea populations
following interspecific hybridization.
The obj ectives of our s tudy w ere: ( 1) t o de tect va riation i n c ompetitive in teractions
between insect-resistant and susceptible plants present at different proportions in mixed stands
under t wo di fferent e xperimental c onditions; ( 2) t o de termine w hether i ntraspecific
competition a mplifies o r d iminishes th e s elective a dvantage o f r esistance; ( 3) to s tudy
adaptive s trategies ( resource allocation) und er v arious c onditions, i ncluding he rbivory and
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