Impact of potassium nutrition on vegetative growth, macronutrient content, and photosynthetic performance in seven cacao (<i>Theobroma cacao</i> L.) cultivars

Limited progress has been made in developing potassium-efficient cultivars for agriculturally important crops due to a lack of knowledge about the biological mechanisms in tolerant cultivars. For Theobroma cacao L. (cacao) cultivars, the characterization of potassium use efficiency (KUE) has remained largely unexplored. This study aimed to characterize the effects of potassium (K) levels on cacao morphology, biomass production, macronutrient (K, N, Mg, and Ca) accumulation, and photosynthetic performance during the vegetative growth phase. Seven cacao cultivars (FEAR5, IMC67, CAU39, FSV85, FSV89, CCN51, and FSV4) were grown under different K regimes (0, 0.04, 0.4, and 4 mM). K deficiency (0 mM) significantly reduced leaf area and biomass production. Cultivar IMC67 exhibited lower leaf, stem, and root biomasses, while FEAR5 showed no significant differences, indicating a greater tolerance to K deficiency. In roots, the accumulation of K, N, and Mg did not change significantly across K treatments for most cultivars. However, in leaves, K deficiency significantly reduced K and N accumulation in IMC67 and FSV85, while no significant difference was observed in FEAR5. The daily integral of net photosynthesis was significantly affected by K deficiency in IMC67, FSV85, and FSV89, but not in FEAR5. Overall, our study indicates cultivar-specific responses in which FEAR5 exhibited resilience under low K conditions, while IMC67 and FSV85 were more sensitive. This study is the first to characterize K nutrition dynamics in these cacao cultivars, providing a foundation for future research to identify genes and pathways crucial for improving K nutrition in cacao and informing breeding programs.