Physiological responses of resistant and susceptible pepper plants to exogenous proline application under Phytophthora capsici stress

Phytophthora capsici Leon. is the main pathogen that limits the production of peppers. In this study, the effects of 1 and 10 mM proline (Pro), prior to exposure of resistant (CM-334) and susceptible (SD-8) pepper seedlings to P. capsici, on some physiological parameters were investigated. A lower Pro concentration (1 mM) was found to be more effective than 10 mM Pro in increasing the stress tolerance of the CM-334 cultivar. Namely, in CM-334 cultivar, the highest chlorophyll a, chlorophyll b, carotenoid, glucose and fructose content and 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activity percentage were detected on the seventh day after application of 1 mM Pro + P. capsici, while the lowest malondialdehyde (MDA) amount was measured on the third day in the same treatment. The highest ferric reducing antioxidant power (FRAP) increase was determined on the seventh day in the 10 mM Pro + P. capsici application. The effects of the same Pro treatments on the SD-8 cultivar somewhat differed; the highest amounts of chlorophyll a, chlorophyll b, anthocyanins, fructose, total protein and endogenous Pro were detected on the seventh day in the 1 mM Pro + P. capsici application, while the lowest MDA amount was measured on the third day after the 10 mM Pro + P. capsici application, the highest DPPH % and FRAP values were detected on the seventh day with 10 mM Pro + P. capsici application. Although some differences were detected between the cultivars, Pro application against the P. capsici stress in general resulted in a positive effect on photosynthetic pigments, soluble carbohydrates and antioxidant capacity in pepper. The exogenous application of Pro helped the non-resistant cultivar to overcome the stress.