Boron, zinc and manganese suppress rust on coffee plants grown in a nutrient solution

Providing adequate nutrition to coffee plants is required to maintain plant health. The effect of five doses (0.05, 0.25, 0.50, 1.0, 2.0 and 4.0 mg L-1) of boron (B), zinc (Zn) and manganese (Mn) on the severity of rust on coffee plants grown in nutrient solution was evaluated. Micronutrients were supplied to seedlings having two pairs of fully developed leaves. The seedling plants were inoculated with spores (10(6) ml(-1)) of the coffee rust pathogen (Hemileia vastatrix). Five assessments of the severity of the rust symptoms were made starting on the 43rd day after inoculation. The area under the disease progress curve for severity (AUDPCS) was calculated. There was a statistical difference in AUDPCS (p < 0.05) with all micronutrients tested. With B and Mn, there was a 15.1% and 52.3% reduction in severity of coffee rust at doses of 4.00 and 0.25 mg L-1, respectively. With Zn there was a 78.0% decrease in AUDPCS. The three micronutrients significantly affected the concentration of total soluble phenols, nevertheless, only Mn influenced the concentration of lignin.