Foliar sprays of NPK fertilizers induce systemic protection against Puccinia sorghi and Exserohilum turcicum and growth response in maize

One spray of 0.1 M aqueous solutions of NPK fertilizers on the upper sides of maize leaves 1, 2, and 3, 2-4 h prior to inoculation, induced systemic resistance (ISR) against northern leaf blight (NLB) caused by Exserohilum turcicum and Puccinia sorghi which were developed on leaves 4, 5, 6, and 7. ISR was expressed as a reduction in the number and area of lesions of E. turcicum and in the number of sporulating or non-sporulating pustules of P. sorghi on leaves 4, 5, 6, and 7. The reduction in the number of NLB lesions ranged from 51% (KH₂PO₄) to 69% (K₂HPO₄) and their size reduction ranged from 73% (KNO₃) to 91% (K₂HPO₄) as compared with water prayed plants. The reduction in the number of pustules of P. sorghi ranged from 66 to 77%. Fertilizers consisting of various combinations of N, P and K in every case induce similar levels of protection in either host-pathogen system. The induced protection was evident regardless of the leaf position or the rate of NPK accumulation in the upper protected leaves. High fresh weight was detected in the induced plants which expressed the greatest induced protection against NLB and common rust. The possible dual use of NPK fertilizers - to supply nutrients to plants foliarly and at the same time to activate the mechanism(s) for induction of systemic protection to P. sorghi and E. turcicum in maize - is discussed.