Nickel enhances rice resistance against Bipolaris oryzae infection

Background and aims Brown spot, caused by Bipolaris oryzae , is one of the most important diseases reducing rice yield worldwide. In order to reduce the use of fungicides, more environmentally friendly alternatives for disease control need to be available to growers. The hypothesis that rice resistance against brown spot could be boosted by nickel (Ni) was investigated in this study. Methods Rice plants (cultivar Metica-1, susceptible to brown spot) were grown in nutrient solution with (0.1 mM Ni; + Ni plants) and without Ni (-Ni plants) and challenged with B. oryzae . Histopathological changes, photosynthetic performance, activities of defense and antioxidant enzymes as well as concentrations of metabolites (hydrogen peroxide, superoxide anion radical, malondialdehyde, phenolics, and lignin) were determined. Results Fungal hyphae massively colonized leaf tissues of -Ni plants compared to + Ni plants resulting in intense cellular damage as indicated by the higher concentration of malondialdehyde. High peroxidase (POX) activity for + Ni inoculated plants occurred at the earlier stage of fungal infection. Great lipoxygenase activity for -Ni plants possibly contributed for brown spot development. The -Ni infected plants showed less photochemical performance (lower values for maximum photochemical efficiency of photosystem II) compared to + Ni infected plants. Conclusion Rice resistance to brown spot was increased by Ni and was a result of the potentiation of defense reactions (greater activities of β -1,3-glucanase and POX) and reduced impairment of the photosynthetic apparatus.