Characterization of Chlorosis and Evaluation of Its Impact on the Phenology of the Cashew Tree in the Bagoué Region, Northern Côte d’Ivoire

Abstract

The cashew tree (Anacardium occidentale L.) occupies an important place in the economy of Côte d’Ivoire, which has become the world's leading producer of cashew nuts since 2015. However, orchards are characterized by low yields, in the order of 350 to 500 kg/ha, attributable to various constraints including foliar chlorosis. This chlorosis, which appears to affect cashew tree remains poorly documented. This study aims to determine the effect of chlorosis on the phenology of the cashew tree in the Bagoué region, in northern Côte d'Ivoire. The experiment consisted of monitoring chlorosis, flowering, and fruiting for 24 months on cashew trees aged 20-25 years. Statistical analyses (Student's t-test, ANOVA, Newman-Keuls, α = 5%) indicated that dominant nutritional deficiencies were linked to nitrogen (47.25%), phosphorus (18.99%), and potassium (18.24%), representing 84.48% of cases. Chlorosis has no effect on the type of flower. Zinc and iron deficiencies have caused significant dried flowers. Increased chlorosis severity reduced fruit number by 75% and decreased the mass of apples during the two production seasons. For nuts, only their mass was influenced by chlorosis during the 2023 - 2024 season, with an average value of 8.61 ± 0.69 g versus 6.63 ± 2.48 g, respectively for high and very high severity levels. Deficiencies in nitrogen, phosphorus, potassium and sulfur were associated with significantly lower production levels. Chlorosis is mainly expressed during the vegetative phase with a prevalence of 88 to 89%, between May and October, and disappears almost completely during the flowering and fruit-setting phase which occurred from November to February of each year. Severe deficiencies in several mineral elements negatively impact flower and fruit production of cashew trees.