Pretreatment with spermidine and proline reverses inhibitory effects of Phytophthora capsici stress in pepper

Abstract

Phytophthora blight (Phytophthora capsici Leon.), which is one of the most important disease factors incurring great economic losses, causes root crown rot. When pepper seedlings were pretreated with 0.1 mM spermidine (spd), 1 mM spd, 0.1 mM spd + 1 mM proline, 0.1 mM spd + 10 mM proline, 1 mM spd + 1 mM proline and 1 mM spd + 10 mM proline and then exposed to P. capsici, they improved their tolerance to subsequent P. capsici-induced oxidative damage. It was detected that cultivar 'Sirena RZ F1' was resistant to P. capsici and it was determined that cultivar 'Sera Demre-8' exhibited sensitive reaction. P. capsici stress caused an increase in total phenolic, malondialdehyde (MDA) and hydrogen peroxide (H2O2) levels, as well as peroxidase (POX) and polyphenol oxidase (PPO) activities in leaves of pepper seedlings. Application of exogenous spermidine and spermidine + proline further increased PPO and POX activity, total phenolic amount. On the other hand, these applications in two cultivars and all days decreased the disease severity, necrosis length and MDA and H2O2 amounts. These data show that antioxidants, especially polyphenol oxidase, peroxidase and total phenolic appear to protect pepper seedlings against stress-related damage. Moreover, spermidine and spermidine + proline have the potential to scavenge directly free radicals and promote the activity of antioxidant enzymes in pepper seedlings under P. capsici stress. In addition, it was also identified that especially 0.1 mM spd, 1 mM spd and 0.1 mM spd + 1 mM proline applications decreased the colony growth of P. capsici and the amount of zoospores. Therefore, we suggest that spermidine and spermidine + proline could play a protective role in protecting the pepper seedlings from P. capsici stress.