The effect of plant defense elicitors on common bean (Phaseolus vulgaris L.) growth and yield in absence or presence of spider mite (Tetranychus urticae Koch) infestation

Background The common bean plants "Phaseolus vulgaris L." is frequently attacked by the two spotted spider mite (TSSM) Tetranychus urticae, causing a substantial decrease in bean plant growth and yield as well as leaflet structure. Therefore, for commercial bean cultivation in the field controlling TSSM infection is necessary. Results Foliar application of salicylic acid (SA) or methyl jasmonate (MeJA) on common bean plants before or after two spotted spider mite infestation proved to be effective in reducing infestations. In most concentrations these elicitors significantly improved common bean plant growth i.e. had a positive effect on plant height, number of branches, shoot dry weight and leaf area per plant and bean yield. SA at 100 mg/l had the strongest positive effect. Moreover, application of elicitors significantly altered leaflet anatomical characters i.e. increased thickness of leaflet blade, thickness of palisade and spongy parenchyma as well as thickness of midrib region of the leaflet and changed the dimension of vascular bundles. Alternatively, TSSM infestation had the opposite effect on these leaflet anatomical characters. Conclusion We conclude that SA or MeJA could be used for controlling TSSM infestation, to improve plant growth and to improve bean yield in the field.