Insect Control and Dosage Effects in Transgenic Canola Containing a Synthetic Bacillus thuringiensis cryIAc Gene

Abstract

The seeds of a number of Brassica L. species are cultivated for the production of oil. Collectively, the oilseed Brassica sp., generally referred to as rapeseed, supply more than 13% of the world's supply of edible oils and rank third behind soybean and oil palm in importance. The term "canola" was adopted by the Canadians in 1979 and used to describe oilseed Brassica cultivars that produce oils containing less than 2% erucic acid and to describe defatted seed meals with less than 30 pmol g-' of aliphatic glucosinolates. Brassica napus L. canola cultivars are currently dominant in U.S. production, although canola-quality Brassica rapa (synonymous with Brassica campestris) cultivars also exist (Raymer et al., 1990).Production of canola in the U.S. has grown at a modest rate during the last 10 years from virtually O in 1985 to 165,000 ha in 1995 (C. Boynton, U.S. Canola Association, personal communication). As production of canola continues to grow, insect problems are expected to become more serious (Lamb, 1989). This may be particularly true as canola production expands in the southeastern United States and California, where mild winter temperatures are likely to lead to increased herbivory, as compared with the much cooler areas (e.g. Canada), where canola has historically been produced. Ubiquitous lepidopteran Brassica specialists, such as the DBM and the CBL, and generalist lepidop-terans, such as the BAW and CEW, may increase in importance where canola is grown in warmer regions (Buntin and Raymer, 1994). This scenario may be especially viable with regard to generalist herbivores, since glucosinolates, a hypothesized antiherbivorant to generalist insects (Giamoustaris and Mithen, 1995), have been bred out of canola-quality rapeseed. Transgenic canola cultivars with insecticidal properties will certainly play a major role in integrated pest management strategies for canola pests (Talekar and Shelton, 1993;Evans and Scarisbrick, 1994). The objectives for this study were 2-fold. (a) To determine the effect of Bt expression in B. napus on antibiosis for severa1 lepidopteran insects. Unlike the related Bt soybean study (Stewart et al., 1996), in which only few, low-expressing synthetic Bacillus thuringiensis insecticidal crystal protein ( B t crylAc) plants were produced, the likelihood of obtaining a wide range of B t expression is greater using a species that is more amenable to genetic transformation, such as B. napus. (b) To develop biological tools to test models pertaining to biotechnological risk assessment. It is possible that a plant species, such as B. napus, that is able to persist in nonagricultural environments could become more weedy in a transgenic form if the transgene confers an increment of fitness and the plant is naturalized in areas of its cultivation. Thus, we developed the B t canola to ultimately test population-leve1 ecological hypotheses.

Genetic Transformation, Recovery, and Characterization of Fertile Soybean Transgenic for a Synthetic Bacillus thuringiensis cryIAc Gene

“…The reasons for the decreased expression are not clear. Using the same construct we (Stewart et al, 1996) have produced transgenic canola with expression levels of up 0.4%, and Singset et al (1996) have produced transgenic peanut with expression levels of 0.18%. It is generally accepted that, when producing severa1 independently transformed plants, expression levels are greatly variable.…”

TransgenicBt-producingBrassica napus:Plutella xylostellaselection pressure and fitness of weedy relatives

“…Although no commercial lines of Bt-producing Brassica napus L. have been released, experimental transgenic Bt-producing B. napus lines have been generated that confer selective advantage in the presence of Brassica-defoliating insects, including diamond back moth (Plutella xylostella L.), cabbage looper (Trichoplusia ni Hübner) and corn earworm [Helicoverpa zea (Boddie)] (Halfhill et al, 2001;Stewart et al, 1996Stewart et al, , 1997Ramachandran et al, 1998a). A number of transgenic Bt-producing Brassica vegetable crops are also being developed, including broccoli (B. oleracea L. var.…”

The Biology of Canadian Weeds. 137. Brassica napus L. and B. rapa L.

“…These findings indicated that transgene location in the genome and accumulation of transgenes may affect fitness in volunteer populations of B. napus. In the United States, Stewart et al (1996) produced a series of transgenic B. napus lines containing the insecticidal Bt transgene and evaluated these in the laboratory and the field (Stewart et al 1997). Under insect selection pressure in the field, transgenic plants had increased fitness due to reduced defoliation compared with their non-transgenic counterparts when allowed to naturalize following cultivation.…”