Calcium and potassium contents in nutrient solution on Phoma leaf spot intensity in coffee seedlings¹

Intensidade da mancha de Phoma em mudas de cafeeiro sob doses de cálcio e de potássio em solução nutritiva

ABSTRACT

Coffee is one of the main export commodities of Brazilian agribusiness. Phoma leaf spot [Phoma tarda (Stewart) Boerema & Bollen] is one of the most important coffee fungal diseases in Brazil. Therefore, this study aimed to evaluate the intensity of Phoma leaf spot in coffee seedlings supplied with different rates of Ca⁺² and K⁺. The study was conducted under controlled conditions in a growth chamber, at the Department of Phytopathology - UFLA, from February 2010 to December 2011. The assay was repeated twice under the same conditions. The nutrient solutions consisted of five concentrations of K⁺ (3, 4, 5, 6, 7 mmol L^-1) and Ca⁺² (2, 4, 6, 8 and 10 mmol L^-1). The experiment was arranged in a randomized block design, with 25 treatments and three replicates, with two plants per plot. The areas under incidence progress curve (AUIPC) and severity (AUSPC) were calculated. At the lowest rate of Ca²⁺ (2 mmol L^-1) and highest K⁺ (6 and 7 mmol L^-1), approximately, the AUIPC was the smallest. For the AUSPC, the lowest rates of Ca⁺² and K⁺ resulted in the lowest severities. Supply of Ca⁺² and K⁺ in nutrient solution reduced AUIPC and AUSPC of Phoma leaf spot, and these nutrients can be recommended for the management of the disease.

Key words:
incidence; severity; Phoma tarda (Stewart) Boerema & Bollen; Coffea arabica L.; mineral nutrition