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Field trial
Seeds of c onventional he rbicide-susceptible B. napus cv. D rakkar, wild B. j uncea, BC1J,
BC1N, and F2 were sown in Giffy 7 pots (Jiffy Prod. Int., Norway) in the greenhouse in order
to promote simultaneous germination, and then the seedlings were transplanted into the field
in Dijon on April 2007. In one experiment, B. juncea, BC1J and F2 were randomly planted in a
bare field. In another place, B. napus, B. juncea, BC1N and F2 were planted randomly in the
field with four blocks. Each block included three rows 30cm apart and 11m long, with one
plant every 0.6 m. The blocks were enclosed in an insect-proof net (12 m wide /15 m large /2
m high, 2 mm mesh) to prevent insect attack, and houseflies were continuously provided in
order to f acilitate r andom p ollination. M ost B. j uncea plants f lowered very early i n t hat
experiment so that they were hardly comparable to the other plant t ypes and were no m ore
considered in the following study.
The B. napus versus B. j uncea morphology ( large v ersus s mall ha bit) w as vi sually not ed
before fl owering. T he fl ower s izes o f a ll BC1N a nd F2 plants w ere v isually rated in tw o
categories: as large as that of B. napus and small. In order to estimate the DNA content of the
plants, w henever pos sible, a pi ece of f resh l eaf w as s ampled t o pe rform f low c ytometry as
described by Akinerden [19] and estimate (the G1 peak) with B. juncea as the control. When
the first pods were about to open, the surviving plants were harvested. The vegetative parts
were separated from the pods and dried in an oven for 48h at 80°C and weighted. Seed weight
and s eed num ber w ere measured. T he w eight of o ne t housand s eeds was cal culated an d
expressed as per-seed weight.
Up to 2000 seeds of every harvested plant were sown in the greenhouse and sprayed with
chlorsulfuron as described above. In order to assign a phenotype to the BC1N and F2 plants,
we considered that a resistant one would ideally produce 75 % of resistant offspring if entirely
self-fertilized, w hile a s usceptible one would p roduce no r esistant s eedlings. Because o f
possible biased segregations after the interspecific h ybridization and the backcrosses on t he
one ha nd, a nd be cause of s ome pot ential c ross-pollination t hat c ould ha ve oc curred i n t he
field on t he ot her ha nd, w e i nterpreted a s s usceptible a ll t he pl ants s howing a p rogeny
containing less than 5 % resistant seedlings, which could correspond to a maximum rate of
fertilization by resistant pollen. Otherwise the plant was designated as resistant.
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