In an experiment, you find that exposing leaves to methyl salicylic acid vapor prior to exposing them to a pathogen results in an avirulent infection, whereas exposing untreated control leaves to the same pathogen results in virulent infection. This is likely an example of:

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Quizplus · Accepted Answer

Systemic acquired resistance is a systemic response of plants to fight against pathogens. It is induced by a signal molecule, such as salicylic acid, which spreads throughout the plant to activate defense responses in uninfected parts of the plant. In this experiment, exposing leaves to methyl salicylic acid vapor prior to exposing them to a pathogen resulted in the activation of systemic acquired resistance, which made the plant resistant to the pathogen. This is why the infection was avirulent.

In an Experiment, You Find That Exposing Leaves to Methyl