Effects of cabbage aphid Brevicoryne brassicae (L.) on yield and its components in canola genotypes (Brassica napus L.)

Canola (Brassica napus L.) is one of oilseed plants that has caught the attention of Iranianfarmers. Cabbage aphid Brevicoryne brassicae (L.) is one of the important pests of canola in Urmia region. Regarding to the importance of this pest, an investigation was carried out under both conditions of field and green house in order to evaluate the resistance of 21 canola genotypes against cabbage aphid during 2005-2008. Under field conditions, two separate experiments, each of three replications were performed based on complete randomized blocks designs under both natural infestation and no-infestation conditions to assess tolerance. Natural infestations occurred in all three experimental years. The evaluation of tolerance under field conditions was performed based on the indices as yield loss, 1000 kernal, the number of seed per capsule, and the number ofcapsules per main and accessory stems. Data analysis indicated highly significant differences (p%1) among different genotypes from the stand point of the studied indices. The genotypes Opera, Sahara and Okapi had the least index of yield loss, and the genotypes Geronimo, Talent and Celisius had the most highest index of yield loss. Based on cluster analysis, the genotypes Opera and Sahara were placed in tolerant group and the genotypes Talent, ARG-91004, Geronimo, Celisius and ARC-5 were classified as members of susceptible group. The evaluation of 21 genotype tolerance based on randomized plots design with three replications was carried out in two separate infected to aphid and control treatments under greenhouse conditions during two experimental years. Results indicated differences (p%1) among various genotypes from the view point of their disformation and stem growth decrease indices. Considering these two indices, two genotypes Okapi, and Opera were placed in tolerant group, and the genotypes Talent, Geronimo, Ebonite, ARG-91004, and ARC-5 were known as members of the susceptible group. The comparison of the results obtained through field and green house experiments illustrated that Geronimo was highly susceptible to cabbage aphid, and the genotypes Opera had an acceptable resistance applicable in the integrated management programs against cabbage aphid.