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 expresse d 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 pu stules was obtained when the foliar spray was applied 6 days before in oculation. One foliar spray of K2HPO4 on leaves 1, 2 and 3, 6 days bef ore inoculation: stimulated plant growth regardless of inoculation. Th e foliar spray on the day of inoculation was less effective in stimula ting 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 di scussed.