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

difficult to predict. Similarly, it is not known if the transgenic plant could totally replace the
wild type. Experiments are needed to answer these questions. However, it is risky to prepare
such “w ild t ransgenic” material, an d ev en ex periments w ith s uch m aterial ar e f orbidden i n
several countries. We therefore simulated the response to insect damage of the resistant and
the w ild p lants b y c lipping le aves. Intact p lants w ithout c lipped le aves r epresented th e
introgressed insect-resistant plants. With different proportions of leaves clipped, and different
ratios of plants with clipped versus plants without clipped leaves in mixed populations, we
investigated th e e ffect o f c ompetition f or limite d r esources o n th e r espective r eproductive
potential of resistant and susceptible plants.
MATERIAL AND METHODS
Eight Brassica juncea seeds were planted at the periphery of 18*18*20 cm pots. In order to
simulate t he p erformance o f t ransgenic i nsect-resistant an d i nsect-susceptible w ild
populations, t he e xperimental tr eatment consisted in c lipping s ome o f th e le aves a s th ey
appeared on s ome plants, but not on ot hers. Leaves were clipped if necessary from the fourleaf
stage up to the opening of the first flower for each plant. When the plants were about 60
cm tall, four poles with ropes were used to maintain the plants within a given volume. The
positions of pot s w ere c hanged e very w eek i n or der t o m inimize t he e dge e ffect. T his
experiment was carried out in a greenhouse at 12 and 22 °C for night and day.
Different percentages of NC plants
We created five treatments of varying proportions of plants with non-clipped leaves (NC): 0,
25, 50, 75 a nd 100 % . O ne out of e very t wo s uccessive l eaves w as clipped i n t he c lipped
plants ( CP). C P a nd N C pl ants w ere di sposed a t r andom i n t he pot s a ccording t o t he
percentage.
Different proportions of clipped leaves
In another set of pots, we assayed four clipping treatments: one of every four leaves (1/4), one
out of two (1/2), two successive leaves out of four (2/4) and three out of four (3/4). For these
84