Assessing the damage of onion thrips (Thrips tabaci) on six cultivars of red bean under field conditions

IntroductionLegumes are a rich source of protein and dietary fiber. A good combination of legume protein with whole grains can eliminate malnutrition and amino acid deficiency in humans. Beans are one of the most important crops that are used in the nutrition of the people of the world and are very important due to their high nutritional value and relatively easy storage. Thrips is one of the pests that reduces bean yield. The different developmental stages of Thrips tabaci, by settling on underside of the bean leaves and feeding on the plant sap, cause silvery leaf spots which the black feces of the pest are visible inside them. These signs of damage indicate the presence of Thrips tabaci. This pest is active in bean fields in all season and cause damage. Onion thrips is the most well-known thrips in the world and causes significant damage to onion, cotton, lettuce, tomato and few other plants. It also carries some viral diseases. Materials and MethodsPhaseolus vulgaris is one of the most important legumes cultivated in most countries of the world. This crop is attacked by various pests including onion thrips. This study was conducted in two years in field condition by planting cultivars Yaghut, Goli, Dadfar, Derakhshan, Ofogh and Akhtar (control) in a randomized complete block design with four replications in two experiments with spraying and non-spraying treatments, at Arak. To assess population changes, sampling was weekly done from the beginning to the end of the growing season. For sampling, five plants were randomly selected from each plot and scored based on the amount of damage and contaminated leaf area. Yield and yield components were also calculated. The results of this study were analyzed using SAS 9.1 statistical software and the means were compared by Tukey test in 1% and 5%. Results and DiscussionIn this study, Yaghoot and Dadfar cultivars had the highest yields with 2775.3 and 2735.3 kg/ha, respectively. On the other hand, Goli cultivar had a lower damage scale and a lower yield reduction percentage compared to other cultivars, but its yield (2110 kg/ha) was lower than other cultivars except the control. The two-year results of this study showed that the highest population of thrips in different stages of nymphs and adults were observed in Akhtar (7.01 and 2.15) and Derakhshan (5.93 and 1.65) cultivars. Population densities of onion thrips on seven cultivars and one soybean genotype were examined by Sedaratian et al. (2010). The results showed that the highest and the lowest population of thrips was observed on (Dpx and KS-3494 genotype) and on (L17 and Taller) respectively. This is not consistent with the results of the present study due to differences in the crop types studied. Kalafchi et al., (2002) examined the resistance of cultivars based on census of onion thrips population and evaluation of crop agronomic characteristics. These researchers evaluated nine onion varieties for damage. Red Azarshahr cultivar with the highest number of thrips and the highest damage to other cultivars was sensitive, and Sefid-Qom cultivar with the lowest number of thrips, was less contaminated. The results of this study are different from the results of recent studies due to differences in employed product and cultivars. The bean plant growth type has a significant effect on the resistance of the cultivars to the two spotted mite. Generalizing this result to the onion thrips needs to more researches. Compounds such as phytic acid, lectin and trypsin inhibitors can affect the biology of the onion thrips. This is similar to the results of the present study due to differences in populations studied as well as differences in yield and damage scale. ConclusionBased on the results of this study, Yaghut due to higher yield and Goli cultivars due to less damage scale priority for cultivation in the area.