Spermine and its interaction with proline induce resistance to the root rot pathogen Phytophthora capsici in pepper (Capsicum annuum)

Abstract

The root rot pathogen Phytophthora capsici can severely damage production of peppers (Capsicum annuum). This study examined the effect of exogenous spermine and spermine in combination with proline on disease severity in pepper inoculated with P. capsici, as well as the effect of the treatments on P. capsici growth and zoospore development. Peroxidase, catalase, and polyphenol oxidase activity, the levels of phenolic compounds, malondialdehyde (MDA), and hydrogen peroxide (H2O2), and fresh and dry weight were measured on the 3rd, 5th, and 7th days after P. capsici infection. Disease severity and size of the necrotic lesions increased with the degree of injury caused by the pathogen and decreased in resistant varieties. The cultivar CM-334 exhibited the highest resistance to P. capsici followed by Amazon F1 whereas other genotypes were susceptible to the disease. Treatments with spermine and spermine + proline prior to inoculation decreased the severity of disease, the length of the necrotic lesions, and the MDA and H2O2 levels in all genotypes, and increased peroxidase, catalase, and polyphenol oxidase activity, the total level of phenolics, and fresh and dry weight, when compared to the untreated, inoculated plants. In addition, 1 mM spermine, 1 mM spermine + 1 mM proline, and 1 mM spermine + 10 mM proline decreased colony growth of P. capsici and zoospore production. This study showed that spermine and spermine + proline induced defense responses and increased resistance to P. capsici infection in pepper.