Transformation with the Arabidopsis bHLH gene 35S:GLABRA3 (GL3) produced novel B. napus plants with an extremely dense coverage of trichomes on seedling tissues (stems and young leaves). In contrast, trichomes were strongly induced in seedling stems and moderately induced in leaves of a hairy, purple phenotype transformed with a 2.2 kb allele of the maize anthocyanin regulator LEAF COLOUR (Lc), but only weakly induced by BOOSTER (B-Peru), the maize Lc 2.4 kb allele, or the Arabidopsis trichome MYB gene GLABRA1 (GL1). B. napus plants containing only the GL3 transgene had a greater proportion of trichomes on the adaxial leaf surface, whereas all other plant types had a greater proportion on the abaxial surface. Progeny of crosses between GL3 + and GL1 + plants resulted in trichome densities intermediate between a single-insertion GL3 + plant and a double-insertion GL3 + plant. None of the transformations stimulated trichomes on Brassica cotyledons or on non-seedling tissues. A small portion of bHLH geneinduced trichomes had a swollen terminal structure. The results suggest that trichome development in B. napus may be regulated differently from Arabidopsis. They also imply that insertion of GL3 into Brassica species under a tissue-specific promoter has strong potential for developing insect-resistant crop plants.

Laboratory and Þeld studies were undertaken to determine the effects of increased numbers of trichomes on seedling stems, petioles, and Þrst true leaves of Brassica napus L., canola, on the feeding and behavior of the crucifer ßea beetle Phyllotreta cruciferae (Goeze) (Coleoptera: Chrysomelidae). Seedlings of ÔWestarÕ canola with genes inserted from Arabidopsis thaliana L. for increased trichome production, called Hairy1, were tested against Westar seedlings in no-choice and choice laboratory tests, and against parental plants and other cultivars grown from seed with and without insecticide in Þeld trials at Saskatoon and Lethbridge, Canada. Analyses of prefeeding and feeding behavior in no-choice tests of Þrst true leaves found that ßea beetles interacted with their host while off Hairy1 leaves more so than beetles presented with leaves of Westar. Beetles required twice as much time to reach satiation when feeding on leaves with increased pubescence than on Westar leaves. In laboratory choice tests, ßea beetles fed more on cotyledons and second true leaves of Westar than on comparable tissues of the transgenic line. In Þeld trials, variations in feeding patterns were seen over time on cotyledons of the line with elevated trichomes. However, all four young true leaves of Hairy1 seedlings were fed upon less than were the parental lines. Feeding on Hairy1 plants frequently occurred at levels equal to or less than on cultivars grown from insecticide-treated seed. This study highlights the Þrst host plant resistance trait developed in canola, dense pubescence, with a strong potential to deter feeding by crucifer ßea beetles.

No abstract

A bioassay arena and a laboratory screening protocol were developed for assessing lines of Arabidopsis thaliana L. (Heynh.) for feeding damage by the adult crucifer flea beetle, Phyllotreta cruciferae (Goeze). The arena consists of a 96-well microtitre plate with a modified top to contain flea beetles and allow ventilation. Eight lines of A. thaliana, arranged in an 8 × 8 Latin square design, were screened simultaneously in each arena using 50 starved flea beetles. Two cotyledons and the first pair of true leaves per plant were rated visually under a dissecting microscope using a visual damage rating scale. The protocol was used to screen 29 wild ecotypes, eight mutant lines and a single transgenic line of A. thaliana. Discrimination between both cotyledon and leaf tissue was apparent for young beetles that were both non-reproductive or reproductive, but not for old reproductive beetles. Differences were observed between Asian and European ecotypes of A. thaliana, suggesting that geographic origin may play a role in susceptibility of Arabidopsis ecotypes to flea beetle feeding. The transparent testa regulatory gene mutants (lines 82, 111, 164) were most susceptible to flea beetle feeding, possibly indicating a role for anthocyanins and/or flavonoids in governing flea beetle susceptibility. Significant variation in damage levels indicates that expression of flea beetle resistance in the Arabidopsis genome is plastic, and that potential exists to use the wide array of publicly available Arabidopsis germplasm as tools in the transfer of resistance to agronomically important host plants.

The bertha armyworm (BAW), Mamestra configurata , is a significant pest of canola ( Brassica napus L. and B . rapa L.) in western North America that undergoes cyclical outbreaks every 6–8 years. During peak outbreaks millions of dollars are spent on insecticidal control and, even with control efforts, subsequent damage can result in losses worth millions of dollars. Despite the importance of this pest insect, information is lacking on the dispersal ability of BAW and the genetic variation of populations from across its geographic range which may underlie potential differences in their susceptibility to insecticides or pathogens. Here, we examined the genetic diversity of BAW populations during an outbreak across its geographic range in western North America. First, mitochondrial cytochrome oxidase 1 ( CO1 ) barcode sequences were used to confirm species identification of insects captured in a network of pheromone traps across the range, followed by haplotype analyses. We then sequenced the BAW genome and used double-digest restriction site associated DNA sequencing, mapped to the genome, to identify 1000s of single nucleotide polymorphisms (SNP) markers. CO1 haplotype analysis identified 9 haplotypes distributed across 28 sample locations and three laboratory-reared colonies. Analysis of genotypic data from both the CO1 and SNP markers revealed little population structure across BAW’s vast range. The CO1 haplotype pattern showed a star-like phylogeny which is often associated with species whose population abundance and range has recently expanded and combined with pheromone trap data, indicates the outbreak may have originated from a single focal point in central Saskatchewan. The relatively recent introduction of canola and rapid expansion of the canola growing region across western North America, combined with the cyclical outbreaks of BAW caused by precipitous population crashes, has likely selected for a genetically homogenous BAW population adapted to this crop.