Physiological, biochemical and molecular responses of young cacao plants grown in compacted and phosphorus-limited coastal plain soil

Authors: TOSTO, T.F. - University Of Santa Cruz - Brazil; ALMEIDA, A.A.F. - University Of Santa Cruz - Brazil; PAIVA, A.Q. - University Of Santa Cruz - Brazil; AHNERT, D - University Of Santa Cruz - Brazil; Baligar, Virupax

Submitted to: Journal of Plant Growth Regulation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/18/2022
Publication Date: 7/9/2022
Citation: Tosto, T., Almeida, A., Paiva, A., Ahnert, D., Baligar, V.C. 2022. Physiological, biochemical and molecular responses of young cacao plants grown in compacted and phosphorus-limited coastal plain soil. Journal of Plant Growth Regulation. 42:2389–2407. https://doi.org/10.1007/s00344-022-10712-3.
DOI: https://doi.org/10.1007/s00344-022-10712-3

Interpretive Summary: In the cacao growing region of Bahia, Brazil, there are large areas of coastal plain soils, which normally do not support cocoa cultivation because of their low fertility and presence of high density subsurface soil layer. Presence of such chemical and physical soil constraints are affecting sustainable production of cacao in this region. In this paper we report that the mechanical stress promoted by soil compaction, associated with variations in the soil phosphorus levels, reduced the root length and increased its diameter in the compacted layer and decreased the activity of most of the enzymes involved in the antioxidant system. Foliar gas exchange and chlorophyll fluorescence emission did not prove to be good indicators to test the levels of imposed stresses. This information on plant traits will be useful for scientists in identification soil areas that have high density subsurface layers and low available phosphorus to improve cacao sustainability and productivity in cacao growing region of Brazil.

Technical Abstract: In the cacao growing region of Bahia, Brazil, there are large areas of coastal plain soils, which normally do not support cocoa cultivation because of their adverse chemical and physical limitations. Objective of the present study is to evaluate the photosynthesis, growth, antioxidant metabolism and gene expression in young cacao plants of the genotype CCN 51 grown in compacted coastal plain soil with fertilization and phosphorus (P) localization. A cohesive yellow latosol was placed in polyvinyl chloride (PVC) tubes, with dimensions of 0.24 m (height) x 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. When analyzing leaf gas exchange and chlorophyll fluorescence emission, no significant differences were found between the evaluated parameters. Changes were observed in the number of leaves, leaf area and dry biomass of the roots. In contrast, the plant height, stem diameter, and the dry stem and leaf biomass were not influenced by the soil densities, location and soil P doses. There were variations in the activity of the enzymes dismutase superoxide, catalase, ascorbate peroxidase and guaiacol peroxidase, 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. The mechanical stress caused by the compaction of the soil of the coastal plain, associated with the location and the doses of P, promoted restrictions to the root growth and development of the whole plant of the cacao genotype CCN 51.