Nitrogen, phosphorus and potassium nutrition effects on flowering and reproduction in an F1 segregating population of the Theobroma cacao L. CCN-51 cultivar

• NPK affects flowering time and intensity, and fruiting in cacao. • Low NPK delays flowering and reduces its intensity. • Excess N reduces flowering compared with optimal N. • Fruiting numbers increase with increasing N dose. • Pollen viability and germination are not affected by NPK availability. Cacao ( Theobroma cacao L.) is a globally significant perennial crop primarily cultivated in tropical regions, where it provides employment to millions of people. Crop productivity is chronically low, and it is imperative to have good information on the cacao plant nutrient demands to maximize yield. The objective of this study was to assess the effects of nitrogen (N), phosphorus (P), and potassium (K) availability on flowering time, flowering intensity, pollen viability, and fruiting of cacao ( Theobroma cacao L.). An F1 segregating population of the CCN-51 cultivar was studied, as this is a well-defined commercially important hybrid cultivar, and because the vast majority of cacao is grown from hybrid seeds. Using a lysimeter setup, young seedlings were grown from the age of 9 months with different levels of N, P, and K loads. Low N, P, and K doses significantly delayed flowering time and reduced the number of flower cushions and flowering intensity. At the highest N dose, flowering intensity was lower than at intermediate N doses. Pollen viability and germination, on the other hand, were not affected by changes in N, P, and K input concentrations. Flowering intensity was the same on the trunk and canopy of a given tree, regardless of the treatment. Nitrogen availability played an important role in natural fruit set in this first year of fruiting, with increasing N resulting in increasing natural fruit set. This study shows the importance of N, P and K optimization for cacao reproduction. Optimizing nutrient availability could have a great impact on its productivity and yield.