Heavy agricultural use of fertilizers has been implicated in degradation of the environmental quality of lakes, rivers and aquifers. There is also widespread public concern about the use of pesticides, including fungicides, on farms and their potential effect on our environment and food. However, it is certain that the use of fungicides as part of intensive agriculture has stabilized our food supply and permitted millions of people to live longer lives. Data from our laboratory and others have indicated that foliar sprays of phosphate and potassium salts can induce systemic protection against foliar pathogens in various crops such as cucumber, maize, rose, grapevine, apple, mango and nectarine. Expression of disease tolerance is dependent on a number of factors including use of fertilizers and pesticides. Therefore, the possible dual role of NPK fertilizers in activation of the mechanism(s) which induce plant protection against pathogens was studied. Data from the application of this concept to various host-pathogen interactions are presented in the present review. A single phosphate spray of 0.1 M solution induced a systemic protection against powdery mildew in cucumber caused by Sphaerotheca fuliginea and against common rust in maize caused by Puccinia sorghi, and northern leaf blight (NLB) caused by Exserohilum turcicum. This systemic protection against powdery mildew in cucumber, common rust or NLB in maize was obtained on upper leaves after NPK fertilizer application on the lower leaves. In both the latter host-pathogens interactions, growth increase was also observed in maize plants as a result of one foliar spray of phosphates. In addition, it was evident throughout all the experiments that a single application of phosphates was effective in suppressing the lesions of powdery mildew on the diseased foliage of cucumber, greenhousegrown roses, field grown mango, nectarine and grapevine. This phenomenon was investigated in combination with fungicides.

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