Physiological Growth Response in Seedlings of Arabica Coffee Genotypes Under Contrasting Nursery Microenvironments

Abstract

Arabica coffee genetic resources and shade-grown coffee landscapes are under threat largely due to human activities and lack of scientific information and understanding on adaptation mechanisms along environmental gradients. The study aims to describe the variability in early physiological growth responses in arabica coffee genotypes of varying geographical areas in Ethiopia, its birthplace. The experiment was carried out under contrasting nursery microclimatic settings at the Jimma Agricultural Research Center in Ethiopia. A split- plot design with three replications of two sunlight regimes and twelve-coffee genotypes were arranged as main and sub-plot treatments, respectively. One-year-old coffee seedlings were used to measure shoot and root growth parts and calculate derivatives on physiological parameters. The results depicted that coffee nursery shade gradients had highly significant influence on leaf mass ratio (LMR) with higher value measured in shaded seedlings. In contrast, seedlings under full-sunlight produced significantly higher shoot mass ratio (SMR). Likewise, LMR was highly significantly different due to natural sunlight regimes, genotypes and interaction effects. Seedlings exposed to direct sunlight had relatively higher root mass ratio (RMR), SMR, canopy area (CA) and leaf area index (LAI). The results also revealed significant responses among coffee genotypes in RMR and LMR. Accessions from the drier Harenna areas exhibited the highest RMR, but least LMR. The accession from Bonga had the highest specific leaf area (SLA) and leaf area ratio (LAR) as opposed to the lowest SLA and LAR in the Yayu and Harenna populations, respectively. Unlike RMR, LARMR was linked to LMR and was low for Harenna and high for Berhane-Kontir. The results also exhibited reduced specific stem lengths for Harenna and Yayu, which had the highest and lowest LAI, respectively. The study shows considerable differences between open sun and shaded seedlings as well as among arabica coffee genotypes for most physiological growth characteristics considered. The results clearly demonstrate the need for shade microenvironments for production of high quality coffee seedlings with balanced shoot and root growth. The study also describes significantly different magnitudes and patterns of relationships between growth traits for future work. In view of the impacts of changing climate on coffee plant, the findings deliver evidence on genetic diversity within arabica coffee accessions of varying geographical areas in Ethiopia. However, further investigations, inter alia, on detail coffee evolutionary, anatomy, molecular, ecophysiological and desirable agronomic traits across seasons and locations for understanding adaptation strategies to environmental stresses and identifying suitable coffee cultivars for specific geographical areas.