Abstract

Thrips tabaci L. is one of the most important pests of onion in Iran. In this research, eight Iranian onion cultivars (Ghermez-e-Azarshar, Sefid-e-Kashan, Sefid-e-Native Khomein, Sefid-e-Improved Khomein, Sefid-e-Qom, Sefid-e-Kordestan, Sefid and Ghermez-e-Shahroud) were cultivated in a RCB design with four replications in Arak, between 2001 and 2003. The number of thrips on five plants was recorded every two weeks and ten days interval on non-sprayed and sprayed plots, respectively. The symptoms of pest feeding, which includes chlorosis and necrosis were rated based on a scale from 1 to 10 for usual damaging and leaf curling another symptom a 1 to 6 scale. The control field was sprayed with current insecticides every 10 days in order to decrease the thrips population. In this study, the highest number of thrips was observed on Ghermez-e-Azarshahr and Sefid-e-improved Khomein and Sefid-e-Shahroud and the lowest number was recorded on non-sprayed fields and then on Ghermez-e-Shahroud, Sefid-e-Kordestan. The highest amount of damage was observed on Ghermez-e-Azarshahr while, the lowest one for Sefid-e-Kordestan and Qom. In non-sprayed plots, the highest yield was recorded for Sefid-e-Kashan and Qom cultivars and the lowest yield for Sefid-e-Kordestan cultivar. The results of the study over the three years showed Sefid-e-Kashan and Sefid-e-Qom as the genotypes resistant to thrips, Sefid-e-improved onion of Khomein as a tolerant genotype and Ghermez-e- Azarshahr having high level of thrips density (more than 25 thrips in each plant) and high level of damage, and leaf curling is introduced as a genotype sensitive to thrips.

Key words: Onion cultivar, Thrips tabaci, resistance.