Progress Toward Development of Canola Resistant to Attack By Root Maggots.

The cabbage root fly, Delia radicum (L.), is a chronic pest of canola (Brassica napus L.) across western Canada, and especially throughout central and northern Alberta.  The root fly causes crop damage when its larvae feed on tissues of the root cortex and vascular tissue.  Research was initiated to investigate potential resistance among intergeneric hybrid genotypes developed from crosses of Sinapis alba L. with B. napus; S. alba is the parental genotype resistant to root fly attack and B. napus is susceptible.  Some of the intergeneric genotypes were resistant to attack by D. radicum, and the mechanism of this resistance was investigated by examining light reflectance properties of susceptible and resistant genotypes, and olfactory responses of flies to these genotypes.  Light reflectance properties varied among susceptible and resistant parental lines, and the hybrids.  The amount of green light reflected from plant foliage was related to D. radicum responses, and indicated that different visual responses of female flies are influenced in part by reflectance properties.  In addition, differential olfactory responses of female flies were apparent:  significantly more males and females responded positively to olfactory cues elicited by the susceptible parent, B. napus, than to the resistant parent, S. alba.  Olfactory responses to several intergeneric hybrids were intermediate to those of the parental genotypes, but significantly lower than to the susceptible parent.  Our study determined that genes for resistance to D. radicum can be introgressed to B. napus, and that light reflectance properties of foliage and volatile odor compounds are responsible, in part, for this resistance.