Dosdall: Developing Root Maggot-Resistant Canola
Date: August 2013
Term: 3 years
Status: Completed
Researcher(s): Dr. Lloyd Dosdall, Department of AFNS, University of Alberta, Edmonton, AB
SaskCanola Investment: n/a
Total Project Cost: $674,076
Funding Partners: ACPC
Project Summary
Root maggots are serious insect pests of canola across western Canada, and especially throughout central and northern Alberta. Researchers at the University of Alberta initiated a project to develop canola germplasm resistant to infestation by root maggots. As a result of the project, resistance to root maggots in new B. napus hybrids has been developed, key biochemical compounds and mechanisms of resistance were identified, which can be used as the basis for introgression of the traits to elite commercial genotypes of canola. This host plant resistance approach integrates well with other root maggot cultural and biological control approaches already in place or being developed, and so can enhance sustainable, long-term control of this pest.
Root maggots are serious insect pests of canola across western Canada, and especially throughout central and northern Alberta. Root maggots cause damage when their larvae feed on canola root tissues. Long-term research has shown that root maggot infestations gradually increase over time when canola is grown continuously on a particular field rather than rotated with a crop that is a non-host for root maggots like wheat or field pea.
Researchers at the University of Alberta initiated a three-year project in 2010 to develop canola germplasm resistant to infestation by root maggots. The development of resistance is one key component among a suite of cultural and biological strategies for controlling root maggot infestations. The study was conducted in collaboration with Dr. L. Kott of the University of Guelph.
The major objectives were: to confirm resistance to root maggots in intergeneric hybrid genotypes developed from crosses of Sinapis alba (resistant) with Brassica napus (susceptible), and then backcrossed with the B. napus parent for several generations, to develop biochemical markers in canola germplasm and to identify the major biochemical pathways associated with root maggot resistance or susceptibility; and to determine the mechanisms of resistance to root maggot attack through behavioral studies of adult root maggots. A combination of field and laboratory trials were conducted at the Universities of Alberta and Guelph for various components of the project.
Researchers crossed several doubled haploid lines, which had previously been identified as having robust root maggot resistance, with elite canola cultivars to produce new hybrid populations. These new populations were assessed under field conditions for their susceptibilities to root maggot attack. Monocultures of B. napus, S. alba and two of the new resistant hybrid genotypes, along with mixed plantings of each genotype were seeded in plots and compared for their resistance. Segregation of resistant and susceptible genotypes occurred in this new population. Biochemical screening confirmed the results obtained in the field assessments.
Three biochemical markers that were constant and linked with root maggot resistance and susceptibility were developed and validated. Two of the markers were associated with resistant genotypes and one was associated with the susceptible lines. The markers helped identify the biochemical pathways and pointed to the presence of flavonoid compounds in the resistant material that alter concentrations of compounds highly attractive to root maggots. Flavonoids can also modify leaf reflectance properties, reducing the attractiveness of resistant canola to ovipositing females.
Researchers used three main types of behavioral laboratory and field studies focusing on visual and olfactory cues, and associational resistance to determine the mechanisms of resistance to root maggot attack. Behavioral studies confirmed that the novel resistant germplasm reflected green and ultraviolet light differently than in susceptible lines, and the odors emitted by resistant lines were less attractive to female flies than those of susceptible genotypes. In field plantings of monocultures of S. alba and B. napus, versus mixed plantings of the two parental lines along with the resistant hybrids, damage to some resistant genotypes increased as a greater proportion of susceptible B. napus plants were included in the mixture. One resistant genotype demonstrated promise for conferring root maggot resistance in susceptible plants in the field trials.
As a result of the project, researchers have developed and confirmed resistance to root maggots in new B. napus hybrids, with the resistance traits derived initially from S. alba. The key biochemical compounds associated with resistance were identified, and the mechanisms of resistance were confirmed in behavioral laboratory and field studies, which can be used as the basis for introgression of the traits to elite commercial genotypes of canola. This host plant resistance approach integrates well with other root maggot cultural and biological control approaches already in place or being developed, and so can enhance sustainable, long-term control of this pest.