The Most Tolerant Canola Genotypes to the Damage of Cabbage Aphid in Miandoab Region of West Azerbaijan Province

Canola (Brassica napus L.) is the most important oilseed crop in Iran that its acreage during the last decade have been significantly increased. Due to increase in the acreage of canola, pests of this crop have been increased correspondingly. One of the most important pests of this crop is Brevicoryne brassicae (L.) that causes direct damage on yield and indirect damage through application of chemical treatments. One of the best ways to reduce the damage of these pests is the use of resistant cultivars. In this study, the resistance of 12 genotypes of canola to the cabbage aphid during two cropping seasons (2009-2010 and 2011-2012) was tested in a field experiment using a randomized complete block design with three replications in Agricultural Research Station of Miandoab. In each year, one experiment was conducted under natural condition and another experiment with the same genotypes was conducted where chemical treatments were applied. Infection indices were calculated from square roots of mean for aphid infected shoot length × average number of aphids in one centimeter of infected stem × percentage of contaminated plots to cabbage aphid and index of yield reduction was calculated based on grain yield of canola genotypes in infected fields compared to control fields. In the autumn survey of treatments, no contamination was observed but spring contamination of canola genotypes with aphid provided suitable conditions to evaluate tolerance of the genotypes. At the grouping of genotypes, the indices of yield reduction for Opera, Zarfam, Orient and Licord were the lowest and these genotypes can be considered as tolerant genotypes in Miandoab and similar regions. Genotypes SLM046 and RGS003 had the highest indices of yield reduction and were grouped as susceptible genotypes.