Study Damage of Cabbage Aphid, BrevicorynebrassicaeL. onsome Canola Cultivars under Field Infestation, in Shahre-kord

Introduction: Cabbage aphid (Brevicorynebrassicae L.) is one of the most important pests of canola in Iran. The pest attacks to the leaves, stems, flowers and pods of the host plant. Feeding and sucking the sap from the plant tissues normally cause leaf and stem deformities and reduce the quality and quantity of the seeds. It was reported that damage caused by the pest can reduce 9 to 77% of the canola yield. Several studies indicated that host plant resistance is an important method which influences population dynamics of B. brassicae and reduces damage of the pest in the field conditions.Using resistant varieties can be the simplest, practical, effective and economical method for the pest control ascomparedwith other control methods. The aim of this investigation was to study population dynamics of the cabbage aphid on different canola cultivars under the natural field infestation and evaluate thepest influence on the studied cultivars/hybrids yield and yield components in Shahre-kord. Material and Methods: Population dynamics and damage of cabbage aphid were studied on five cultivars (including: Okapi, Licord, Talaye, Modena, Tasilo) and two hybrids (Hyola 308 and Hyola 401) of canola based on the completely randomized block design in three replicates under the field conditions. To study population dynamics of the pest, sampling was started from the beginning of the infestation (the first decade of April) and continued weekly until harvesting time. For this purpose, five plants in each replicates were selected randomly and the number of aphids (nymphs and adults) was counted on 10 cm of each stem. Moreover, at the harvesting time, 10 plants from each replicate were selected randomly and the yield and yield components includingnumber of pods, number of seed per pods, weight of 1000 seeds were measured. Statistical analysis was done using Proc ANOVA in SAS 9.1 software. Results and Discussion:Ourstudy addressed the seasonal activity and population dynamics of the canola aphid on different canola varieties under the field conditions.The results indicated that the activity of cabbage aphidwas started from the first decade of April and reached to the highest level at the flowering stage at the third decade of May. The highest (450 aphids/plant) and lowest (200 aphids/plant) population density were observed on Talaye cultivar and Hyola 401 hybrid, respectively. Similar results were reported by KhazduziNejadJamali et al. (2012) and Sarwar et al (2002).Mean comparison of yield and yield components in different canola cultivars and hybrids under the field infestation to cabbage aphid showed the highest (83.47) and lowest (12.69) number of pods in Hyola308 hybrid and Modena cultivar, respectively. Moreover, the highest (13.27) number of seeds per pod was observed in Tasilo cultivars, whereasthe highest seed weight was identifiedin Tasilo and Hyola hybrids. Themaximum and minimumyieldwere, respectively, recorded forTasilocultivar(0.41 gr/plant) and Modenacultivar(0.01 gr/plant).Our finding was similar to the results of Monfared et al (2003) who reported that Hyola 308 and Hyola 401 hybrids and Talaye and Licord varieties were resistant to the cabbage aphid. Keyhanian et al (2008) observed the highest pest population on Licord cultivar which supports our findings. However, they reported the lowest yield in Hyola401 which is in contrast with our results. The differences between the results canbe due to the influence of environmental factors on the studied cultivars. Conclusion: Our results demonstrated that Hyola 401 hybrid had the highest number of pods per plantand number of seed per pod and Tasilo cultivar had the highest yield and seed weight. In addition, the lowest yield and yield components was found for Modena cultivar. Therefore, Tasilo was the most suitable and Modena was the least suitable cultivar for growingin Shahre-kord.Sincepesticide applicationto control the pest has several disadvantages such as increasing production cost, developing resistant races, destroying natural enemies and environmental hazards,integrated pest management based on the host plant resistance is, therefore, essential for controlling the canola aphid. Usingthe resistant hybrids and cultivars can reduce insecticides hazards, protect natural enemies and help integrated management of the canola aphid