Growth, physiological, nutrient uptake efficiency and shade tolerance responses of cacao genotypes under different shades

Authors: AREVALO-GARDINI, E. - Tropical Crop Institute (ICT); FARFAN, A - Tropical Crop Institute (ICT); BARRAZA, F - Tropical Crop Institute (ICT); AREVALO-HERNANDEZ, C. - Tropical Crop Institute (ICT); ALEGRE, J. - La Molina National Agrarian University; Baligar, Virupax

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/27/2021
Publication Date: 7/30/2021
Citation: Arevalo-Gardini, E., Farfan, A., Barraza, F., Arevalo-Hernandez, C.0., Alegre, J., Baligar, V.C. 2021. Growth, physiological, nutrient uptake efficiency and shade tolerance responses of cacao genotypes under different shades. Agronomy. 11:1536. https://doi.org/10.3390/agronomy11081536.
DOI: https://doi.org/10.3390/agronomy11081536

Interpretive Summary: Cacao is an understory tree that is cultivated under varying cultural practices ranging from full-sun monocultures to multi-strata agroforestry systems. Under multi-strata agroforestry cultivation, cacao is subjected to excess shading due to overgrown and unmanaged shade trees. Intra specific variations among wild and domesticated juvenal cacao genotypes were observed for growth, physiological and nutritional traits and tolerance to shade and the negative affect of heavy shading on cacao growth and development. Among 58 genotypes tested, 14 genotypes showed tolerant to shade. Genotypes that tolerate excess shade might be useful plant types to maintain productivity and sustainability in cacao agroforestry systems. This information will be useful to farmers and extension worker to improve production of cacao under agroforestry systems of management and cacao breeder to breed improved cultivar suitable for agroforestry production systems.

Technical Abstract: Cacao is an understory plant and invariably cultivated under full-sun monocultures to multi-strata agroforestry systems, where cocoa trees are planted together with fruit, timber, firewood, and leguminous trees, or grown within thinned native forests. Under such system of cultivation cacao is subjected to excess shade due to over grown and unmanaged pruning of shade trees. Cacao tolerant to shade, and maximum photosynthetic rate occurs around irradiance of 400 µmol m-2 s-1 but excess shade reduces required irradiance further which is detrimental to maintain photosynthesis and growth functions. In recent years, cacao is increasingly cultivated in open canopy with limited number of shade trees and under such systems of management cacao has been subjected high levels of irradiance. Intra specific variation known exist in cacao for required saturation irradiance. Greenhouse study was implemented with 58 cacao genotypes selected from 4 geographically diverse groups: (i) wild cacao genotypes from river basins of Peruvian Amazon, (ii) Peruvian farmers’ genotypes, (iii) Brazilian selections genotypes and (iv) national and international cacao genotypes. All the cacao genotypes were subjected to two levels of photosynthetic photon flux density (PPFD) of 1000 (50% shade) and 400 (80% shade) µmol m-2's-1. Intra specific variations were observed for growth, physiological and nutritional traits and tolerance to shade. Cacao genotypes tolerant to shade were: UNG-27 from the wild cacao collection; ICT-2171, ICT-1506, ICT-2142, ICT-1087, ICT-2172 and ICT-2173 from the Peruvian farmers’ collection; PH-21 and CA-14 from the Brazilian collection; POUND-12, ICS-95, ICS-39, ICS-1 and UF-613. Genotypes that tolerate excess shade might be useful plant types to maintain productivity and sustainability in a agroforestry systems of cacao management systems.