Physiological, Biochemical, and Molecular Responses of Young Cacao Plants Grown in Coastal Plain Compacted Soil, with Location and Phosphorus Limitation.

In the cacao growing region of Bahia, Brazil, there are large areas of coastal plain soils, which normally do not support cacao cropping because of their adverse chemical and physical limitations. The main objectives of this work were to evaluate growth, photosynthesis, antioxidative metabolism, and gene expression in young plants of CCN 51 cacao genotype grown in coastal plain compacted soil, with location and phosphorus limitation. A cohesive yellow oxisol was placed in polyvinyl chloride tubes with 0.24 m (height) × 0.1 m (internal diameter). The tubes were subdivided into three rings of 0.08 m height connected with tape. In the upper and lower rings soil density was maintained at 1 kg dm⁻³. In the lower ring, two levels of soil P (low—200 mg dm⁻³ soil and ideal—400 mg dm⁻³ soil) were evaluated. In the middle ring five soil densities (1; 1.3; 1.4, 1.5, and 1.7 kg dm⁻³) were maintained. Changes were observed in the leaves number, leaf area and root dry biomass. There were variations in the activity of dismutase superoxide, catalase, ascorbate peroxidase and guaiacol peroxidase enzymes, involved in antioxidative leaf and root metabolism. Changes in the expression of the Cu–Zn–sodcyt, Cu–Zn–sodchl and per-1 gene transcripts were observed. Mechanical stress promoted by soil compaction, associated to variations in dose and P location, reduced the root length of the young cacao plants in relation to the volume, increased its diameter in the compacted layer and decreased the activity of most of the enzymes and expression of genes related to antioxidative metabolism, mainly in root level. [ABSTRACT FROM AUTHOR]