The efficacy of seven plant extracts (neem, fennel, lavender, thyme, pennyroyal, salvia and asafetida) in controlling postharvest of apple (caused by Botrytis cinerea) was evaluated in vitro and in vivo. In vitro, all plant extracts treatments inhibited spore germination. Inhibitory rates of pore germination was 17.41 and 20.83% for neem extract treatment (methanolic and aqueous extracts, respectively) with significant difference compared to control (73.6 and 85.33%) for aqueous and methanol extracts. In the storage conditions, the application of aqueous extract of neem (at concentration of 25%) resulted in 89.11% reduction of disease severity compared with the untreated control. Results of enzymes activity showed the plant extracts can increase the activity of peroxidase, phenylalanine ammonia-lyase, β-1,3-glucanase and polyphenol oxidase in the presence of pathogens, in apple fruits. However, the results of this research revealed that application of neem extracts was more effective than the application of other plant extracts. According to this study, it could be concluded that plant extracts may be useful to control postharvest disease as a safe alternative option to chemical fungicides.

The effect of salicylic acid (SA) on antioxidant enzymes activities in wheat infected with Mycosphaerella graminicola was investigated. Different concentrations of SA (0 and 2mM) were sprayed on susceptible and tolerant cultivars of wheat at a two-leaf stage. Enhanced activities of peroxidase, catalase, phenylalanine ammonia lyase, and polyphenoloxidase were determined in two wheat SA-treated cultivars in the presence or absence of pathogen. The results showed that the application of SA was more effective on antioxidant activities than pathogen. However, the highest activities of all tested enzymes were detected in cultivars treated both with SA and pathogen. Although in the earliest time of infection the antioxidant enzymes activities in susceptible cultivar were weaker than in the tolerant cultivar, the enzymes activity enhancement by SA in susceptible cultivar was observable, too. These results suggest SA as plant defense inducer could be an effective agent against M. graminicola in wheat.

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Plants have many defense mechanisms against pathogens that can be stimulated and activated by some microorganisms or chemicals. There are five types of induced resistance in plants that are included: localized acquired resistance, systemic acquired resistance, systemic gene silencing, induced systemic resistance, and systemic wounding response. Systemic acquired resistance is the most important type of induced resistance in plants that result in continuous and prolonged protection from infection against a wide range of pathogens. Formation of pathogenesis related proteins, alteration of cell wall with sedimentation and binding of polysaccharides, proteins, glycol-proteins, phenols, phytotoxins, and ligninification are the stages of occurrence of this type of resistance in plants.