Significance of foliar sprayed salicylic acid in kidney bean resistance against Tetranychus urticae (Trombidiformes: Tetranychidae) attack

The two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), is capable of dramatically decreasing growth and yield of bean plants (Phaseolus vulgaris L.) in Egypt. Aiming to offer an alternative method to be used for its control, we evaluated the effect of salicylic acid (SA) on induced resistance in bean seedlings against spider mite attack. Possible defense responses that were involved were also elucidated. The 9 and 18-day results proved that foliar application of SA at 50 and 100 mg l-1 has a clear influence on containing mite populations, with higher efficiency observed at the higher concentrations. Consistent with the incidence of induced resistance and defense reactions, the remarkable increase in peroxidase (POD), polyphenol oxidase (PPO) activities and phenolic and flavonoid contents was detected in SA and/or the infestation bean treatments. In contrast, catalase (CAT) activity showed a different trend, as it was significantly decreased in the leaves subjected to individual infestation. The highest levels of all tested enzymes and compounds were noticed after 18 days at 100 mg l-1 SA combined with the infestation treatments. In addition, increased mite population density led to a reduction in chlorophyll content, but SA was able to partly revert that loss in a concentration and time–dependent manner with 100 mg l-1 concentration being more effective at 18 days following application. Together, these results indicate that SA treatments at the proper concentration and time could potentiate the resistance in bean plants against T. urticae.