Investigating the Quantitative and Qualitative Characteristics and Resistance to Thrips of Onion Genotypes

To evaluate quantitative and qualitative traits as well as thrips resistance of onion genotypes, an experiment was conducted at Behbahan Agricultural Research Station, Behbahan, Khuzestan, Iran from 2013 to 2015. The experiment was a split plot based on a randomized complete block design with three replications. Pesticide-treated and pesticide-free plots were considered as sub plots and ten onion genotypes (Behbahan, Padook, Ramhormoz, Iranshahr, Borazjan, Dorcheh Esfahan, and Kamerei Khomain landraces, Primavera and Texas early grano cultivars and improved population of Behbahan onion) were considered as main plots. The seeds were sown in nursery bed in early October and the seedlings were transplanted into the field at 2-3 leaf stage in mid-November. The bulbs were harvested when 50-80% of foliage top had fallen and collapsed. Among different thrips species the Thrips tabaci Lindeman was the predominant in the experimental field. To control the thrips, the pesticide was applied 4 and 3 times in the first and second years of experiment, respectively. Leaf length, total and marketable yield, mean bulb weight and bulb dry matter percentage were significantly higher in the pesticide-treated plots than in the pesticide-free plots. However, thrips population was significantly lower   in the pesticide-treated plots than the pesticide-free ones. Also, the spraying had not significant effect on the number of leaves. Due to the lack of significant differences between total and marketable yield of Ramhormoz genotype in the pesticide-treated plots and pesticide-free plots, it can be concluded that this genotype is capable of resisting thrips, at least in part, compared to the other genotypes. While Texas early grano cultivar produced the highest yield in the pesticide-treated plots, in the pesticide-free plots the highest yield belonged to Primavera cultivar. According to the results obtained, it can be concluded that the Texas early grano and Primavera cultivars are suitable for cultivation in the presence and absence of anti-thrips pesticides, respectively.