Treatment of Lime Witches’ Broom Phytoplasma-Infected Mexican Lime with a Resistance Inducer and Study of its Effect on Systemic Resistance

Destruction caused by plant diseases is terrible. Mexican lime witches' broom (MLWB) is a phytoplasma disease, which has caused considerable damage in Mexican lime tree in southern parts of Iran. In order to protect the plant against this pathogen, it is required to apply an appropriate treatment to induce resistance. Moreover, for better comprehension of disease mechanism, the analysis of phytohormones as one of the most critical basic components in plant cells, probably involved in resistance mechanisms, is of great importance. In this work, Mexican lime trees infected with lime witches’-broom phytoplasma (LWBP) were treated with Previcur EnergyTm (31% fosetyl-Alluminum plus 53% propamocarb) 4/000 as the resistance inducer against phytoplasma. In the next step, phytohormone levels in healthy Mexican lime were compared with those of infected and treated lime trees. For analysis of phytohormones, one-step dispersive solid phase extraction (DSPE) combined with liquid chromatography-tandem mass spectrometry-multiple reaction monitoring (LC–MS/MS-MRM) mode was used. A total of 54 phytohormones including cytokinins, auxins, jasmonates, gibberellins, salicylic acid and abscisic acid groups were simultaneously analyzed for treated, infected, and healthy plants. Totally, 18 phytohormones from plant leave extract were detected, among which levels of 11 phytohormones including SA, JA, JA-Phe, JA-Ile, JA-Leu, OPDA, CZ, iP7G, cZ9G, TZr and 2MeStZR were significantly changed in both infected and treated plants. Result of the present study indicated that the applied treatment was able to reduce the severity score in plant. On the other hand, phytoplasma (as a biotic stress) and treatment with Previcur EnergyTm (as a resistance inducer) could affect fundamental processes in plant via regulation of phytohormone levels.