Resistance Components of Canola, Brassica napus L. Genotypes to Cabbage Aphid Brevicoryne brassicae (L.)

Cabbage aphid is a key pest of canola. Resistance of 21 canola genotypes to cabbage aphid was studied in a completely randomized block design in the field and greenhouse during 2006-2008. In each year، two separate experiments، each with three replications، were performed under natural infestation and no-infestation conditions in the field. Infestation index and functional reduction of grain yield were evaluated in the field experiment to compare the tolerance of the genotypes. In order to evaluate greenhouse tolerance، the genotypes were planted in pots at two sets of completely randomized design. One set of plants of each genotype was infested with insects while another set were kept insect-free to be used as control for the same genotype. Reduction of stem length and damage indices were recorded. To evaluate antibiosis effect of genotypes، intrinsic rate of increase of cabbage aphids were estimated on each genotype in a completely randomized design with 10 replications. Results showed that infestation index rate was different among genotypes، years and sampling times. The genotype ‘Opera’ had the lowest infestation index (4. 23). Combined analysis of variance for traits of grain yield loss and its components indicated significant differences among genotypes. Damage indices and stem length reduction of genotypes were significantly different in the greenhouse. Intrinsic rate of increase (rm) also was significantly different among the genotypes in the greenhouse. ‘Okapi’ with rm= 0. 21 female/female/day had the lowest intrinsic rate of increase. In conclusion، ‘Okapi’ and ‘Opera’ genotypes should the highest plant resistance index، 23. 58 and 19. 78، respectively.