Development of rutabaga cultivars resistant to cabbage maggot

Project Code PRR10-140

Project Lead

Laima Kott  University of Guelph

Objective

To Develop and promote adoption of resistant cultivars to cabbage maggot in rutabaga

Summary of Results

Background

Brassicaceae crops in all production regions in Canada suffer from losses attributed to the cabbage maggot, Delia radicum L. (Diptera: Anthomyiidae) and closely-related species. Its management relies primarily on applications of chemical insecticides. Three active ingredients are currently registered for use against this pest, including cypermethrin (in British Columbia only), cyantraniliprole, and chlorpyrifos. When this project was initiated, growers relied heavily on chlorpyrifos; however, research in 2013 confirmed that 75% of populations tested in British Columbia were chlorpyrifos-resistant. Additional studies are currently ongoing to document the extent of resistance to chlorpyrifos in Brassica growing regions nationwide. Reduced risk alternatives are required to replace conventional insecticides and to become part of routine integrated management of cabbage maggot in these crops.

Approaches

The project aimed to develop and promote adoption of rutabaga cultivars resistant to cabbage maggot, an approach strongly supported by industry. Funded for the first three years by the rutabaga growers’ association in Ontario (SWORGA, South Western Ontario Rutabaga Growers’ Association), Dr. Laima Kott established the testing protocols and developed the first generation of plants with resistance to the pest. Growers from all regions expressed an interest in seeing this work completed and the project became part of the national Reduced-Risk Strategy for Cabbage Maggot Management in Brassica Crops. In the following years, screening and back-crossing were designed to produce breeding lines that carry resistance to cabbage maggot while expressing the phenotype of the most popular commercially rutabaga cultivar, the Laurentian.

Results

The work was accomplished by utilising both classical and laboratory breeding methods. The gene of resistance originated from a cruciferous weed, Sinapis alba, which was first introduced into canola by numerous breeding cycles to form the resistant canola double haploid (DH) line RM01-700. Moving the trait from the canola line into rutabaga required a minimum of 4 backcrossing cycles. Each cycle consisted of crossing the root maggot resistant parent (canola in the first cross) by rutabaga cv. Laurentian. Plants of the F1 hybrid generation were subjected to double haploid production wherein all progeny were 100% homozygous. These DHs were screened to identify those with the strongest resistance to cabbage maggot. A new backcrossing cycle then took place using the selected DH lines as parents for crossing to Laurentian, which would then become the backcross (BC1) generation. With each cross the rutabaga proportion of the genotype was increased, while the canola portion of the cross was diminished, with the exception that the resistance trait was maintained from the canola parent. After 4 such breeding cycles, ending at backcross BC3, the resulting product were rutabaga genotypes carrying the resistance trait. The BC3 generation makeup of the progeny is 93.5% rutabaga and 6.5% canola. Horticulturally, they resemble the Laurentian rutabaga in terms of root shape, size, colour, and flavour.

Between the crossings, the DH lines were subjected to laboratory tests to select the line(s) with best resistance to be used as a parent in the next crossing generation. Leaf extracts of the DH rutabagas were analyzed for the presence and quantity of specific chemical markers that correspond with the resistance trait. Field trials were also conducted as a definitive method to assess root maggot damage in the new lines. The first group of BC3 DHs was ready for field tests in 2013, and subsequently lines were selected from that initial population. Trials were carried out in a rutabaga producer’s field near Milverton, Ontario, an area known to have history of cabbage maggot infestations. Commercial management practices common to the area were used, including crop rotation between subsequent years. The tested lines were compared against the commercial Laurentian rutabaga crop grown on the same farm (‘sprayed control’), and against untreated control from the trial plots (‘unsprayed control’). Trials were conducted in four replications and the rutabagas were scored as the percent of damaged area per root in ten plants per plot.

Three DH lines, identified as 88, 136, and 148, showed the least level of root maggot damage among all the new lines. They also exhibited significantly lower level of damage as compared with the unsprayed Laurentian check. The University of Guelph holds the Intellectual Property over this technology and its Catalyst Centre has offered these lines to interested parties for seed production and testing through a commercialization process. Seed production and testing is underway, and a decision regarding commercial production is pending.

Should this resistant cultivar become available to growers, the new rutabaga would potentially require fewer insecticide applications than is currently recommended. In turn, this could reduce the costs associated with the purchase and the application of these chemicals. It will represent a safer alternative for human health and the environment, and be less vulnerable to restrictions when exporting the commodity to international markets.

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