Foliar Application of Melatonin Alleviates the Deleterious Effects of Drought on the Three Most Cultivated Capsicum Species in Africa

Signaling molecules such as melatonin can modulate drought, which continues to be a serious threat to plant productivity across the world. Capsicum is an economically important crop valued for its piquancy and nutritional content, but is quite sensitive to drought. This study investigated the effect of two levels of foliar application of melatonin (0 and 50 μM) on growth parameters, pigment accumulation, and osmolyte and inorganic ion content of three Capsicum species (C. frutesence, C. chinense, and C. annum) under well-watered as well as mild and severe drought conditions. Drought exerted negative effects on growth and development of the Capsicum spp., as indicated by changes in height, decreased leaf area, biomass, and photosynthetic pigment concentrations. Drought strongly decreased chlorophyll a, b, and carotenoid content, but increased root biomass, total soluble sugar, and proline concentrations of Capsicum compared to well-watered plants. In C. frutesence, severe drought significantly enhanced Na⁺ and SO₄²⁻, while mild drought increased Ca²⁺ and SO₄²⁻. Mild and severe drought increased Na⁺, decreased K⁺ and Ca²⁺, and had no significant effects on Cl⁻ and SO₄²⁻ in C. chinense and C. annum. Foliar application of melatonin had positive but varying effects on Capsicum, as indicated by differences in growth, photosynthetic pigments, and ion accumulation. These findings pointed to beneficial effects of foliar application of melatonin in facilitating and improving drought tolerance of Capsicum via increased osmolyte accumulation, pigments, and total concentration of inorganic ions under drought conditions.