Foliar spray of phosphates induces growth increase and systemic resistance to Puccinia sorghi in maize

A single foliar spray of 0‐1 M phosphate salts solution was applied to the upper side of maize (cv. Jubilee) leaves 1,2 and 3 at the five‐to six‐leaf stage, 2‐4 h before inoculation with Puccinia sorghi. This treatment induced systemic resistance against common rust as expressed by 98% reduction in the number of pustules of P. sorghi developed on leaves 5, 6 and 7, There was no damage or chlorotic stippling on the induced leaves (1, 2 and 3) as a result of the phosphate spray, A less effective, but still significant. reduction (90%) in the number of pustules was obtained when the foliar spray was applied 6 days before inoculation. One foliar spray of K₂HPO₄ on leaves 1,2 and 3,6 days before inoculation, stimulated plant growth regardless of inoculation. The foliar spray on the day of inoculation was less effective in stimulating growth. Appropriate mixtures of phosphate solutions revealed that the level of protection was not necessarily dependent on the gradual changes in the pH of the solution. The possible dual use of phosphate salts as foliar fertilizers and as agents for induced resistance is discussed.