Resistance to cabbage aphid (Brevicoryne brassica L.) in 27 rapseed(Brassica
napus L.) lines, hybrids and varieties, and a wild species of Sinapis arvensis were evaluated in a field experiment under natural infestation in 2000-2001. The experiment was arranged in a completely randomized block design with four replications. To compare resistance of rapeseed entries to aphid, a sampling method called Infestation Index was used as a criterion. This index was calculated by multiplication of infested stem length by proportion of infested plants. Sampling was extended from flowering stem stage to harvest. In the sampling method, length of infested stem that was covered by aphid colonies was measured, and plants, which were infested by more than one centimeter in length, counted as infested plants. Means of infestation index in each sampling interval indicated that trends of infestation from beginning to mid April tend to increase and decrease thereafter. In this experiment, Hyola308, Hyola401, Eurol, PF, Okapi, Hyola330 and Shiralee were recognized as resistant as they were not significantly different from Sinapis arvensis as a resistant check. Remaining entries were classified as partial resistant and susceptible, according to their levels of infestation.
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