Effect of Transplanting Density on Leaf Yield and Pest Tolerance of Amaranth (Amaranthus cruentus) in the Tropical Conditions

Amaranth, a food crop with a high nutritional value, stands out for its great adaptability to environmental conditions. From a sustainable agriculture perspective, adjusting the transplanting density is an essential lever for improving plant productivity and health. This study aims to evaluate the impact of transplanting density on leaf yield and tolerance to pests of amaranth. It was carried out in the south of Côte d'Ivoire, a region with a bimodal equatorial climate alternating rainy and dry seasons favourable to this crop. The trial was conducted using a randomized full block design with three transplanting densities : D1 (20 × 20 cm), D2 (10 × 20 cm) and D3 (5 × 20 cm), with three replicates. Amaranth plants were transplanted onto 16 m² boards, previously ploughed. The observations focused on the number of branches, the flowering time, the leaf yield (t/ha) and the sensitivity to pests, evaluated on a scale of 1 (very tolerant) to 5 (very sensitive). The results indicate that transplanting density positively influences the number of twigs and leaf yield. Density D2 (10 × 20 cm) produced the highest number of twigs (686 ± 20) and the highest leaf yield (16.0 ± 0.9 t/ha). Better tolerance to stem necrosis was also observed at this density (score 3.3), compared to a higher sensitivity (score 4.3) at density D1 (20 × 20 cm). In contrast, the spike density did not have a significant effect on the degree of attack of the caterpillar. Similarly, the flowering time remained stable, around 45 days after transplanting. These results highlight the importance of choosing an optimal transplanting density to improve productivity and resistance to pests without disrupting the phenological cycle. In this respect, the D2 density appears to be the best compromise, combining high productivity with better plant health.