Weed control is an important factor for the successful production of canola
[Brassica napus (L.) and B. rape (L.)] on the Canadian prairies. Tradition
ally, various pre- and post-emergent herbicides have been used to achieve t
he required level of weed control. Recently, B. napus has been genetically
engineered to express tolerance to the broad-spectrum, post-emergent herbic
ide, glufosinate-ammonium [2-amino-4-(hydroxymethylphosphinyl)butanoic acid
]. This study was conducted to determine the genetics of glufosinate-ammoni
um tolerance in a series of Agrobacterium-mediated transgenic lines of B. n
apus carrying the phosphinothricin-acetyl transferase (pat) gene from Strep
tomyces viridochromogens (Krainsky) Waksman and Henrici. Twenty R-1:F-2 and
19 R-1:BCF1 populations derived from 20 R-1 transformants were analyzed fo
r the number of transgenic inserts on the basis of their segregation patter
n for herbicide tolerance. Fifteen of the 20 transgenic lines had a single
insertion of the pat gene which behaved in a Mendelian manner and five had
insertions at two independent loci. Ten transgenics with single gene insert
s crossed in a half-diallel fashion were used to establish allelic relation
ships of transformants. The results indicated that the insertions had occur
red at different loci within the plant genome with a possibility of an asso
ciation between inserts in one case. It was concluded that transformants sh
ould be analyzed for number of transgene inserts and for genetic stability
before they may be used in breeding programs for the development of glufosi
nate-ammonium tolerant B. napus cultivars.