Physiological and metabolic changes of Cucurbita pepo leaves in response to zucchini yellow mosaic virus (ZYMV) infection and salicylic acid treatments

The changes of some physiological and biochemical parameters in pumpkin (Cucurbita pepo cv Eskandarani) leaves associated with zucchini yellow mosaic virus (ZYMV) infection and the effect of exogenous application of salicylic acid (SA) were studied in this paper. In comparison to the untreated leaves, ZYMV infected leaves showed many symptoms, including severe mosaic, size reduction, stunting and deformation. Results from analysis of physiological parameters indicated that viral infection and SA treatments affected metabolism. Viral infection decreased pigment, protein and carbohydrate levels. But with all SA treatments, the protein and carbohydrate contents are noticeably increased. Moreover, the other biochemical parameters showed variable alterations. The peroxidase (POX, EC 1.11.1.7) activity and proline contents were induced by both viral infection and SA treatments. In addition, protein patterns represent some newly synthesized polypeptides which reflect formation of pathogenesis related proteins in all treatments. SA treatment increases the plant resistance against ZYMV. This can be noticed through reduction of percentage of the infected plants, decrease in disease severity and virus concentration of the plants treated with SA then inoculated with virus. All results show significant changes in metabolism affected by either viral infection or SA treatments and also indicate that exogenous SA plays an important role in induction of defense mechanism against ZYMV infection.