This invention provides novel methods for improving plant quality and yield in the presence of pathogens. The method increases the levels of pathogenesis-related proteins, such as PR1, phenylalanine ammonia lyase, or plant cell wall proteins such as hydroxyproline-rich glycoproteins, in a plant by contacting the plant with a plant systemic inducer and a reactive oxygen species wherein the amount of the reactive oxygen species is sufficient to increase the amount of the pathogenesis-related protein above the level induced by the plant systemic inducer in the absence of the reactive oxygen species. A preferred reactive oxygen species is peracetic acid; a preferred plant systemic inducer is salicylic acid.