Variations in Leaf Water Potential in the Wild Ethiopian Coffea arabica Accessions under Contrasting Nursery Environments

The study was conducted with the aim to compare the variability among the wild coffee germplasm accessions in diurnal leaf water potential (LWP, ?L) under contrasting shading and irrigation environments. Twelve coffee accessions were evaluated under two shading (moderate shading and full sun radiation) and irrigation (well watered and water stressed) regimes at nursery site. The diurnal leaf water potential was measured with a pump-up pressure chamber twice a day (predawn and midday) at every 4-day intervals for a two week drought stress imposed period. The results depicted significantly maximum predawn (?L = -0.66±0.43 MPa) and midday (?L = -1.35±0.24 MPa) leaf water potential in shaded seedlings as compared with those in full sunlight conditions. Likewise, significant (p<0.05) variation in midday LWP was measured on the 4th day after irrigation (4-DAI). The lowest (?L = -1.54 MPa) and highest (?L = -1.32 MPa) midday LWP were recorded for the Bonga and Berhane-Kontir coffee germplasm accessions, respectively. Moreover, relatively low (?L = -0.87 MPa) and high (?L = -0.73 MPa) predawn LWP were recorded for the Bonga and Berhane-Kontir coffee germplasm accessions with the lowest change in diurnal ?L of -0.75 and -0.73 MPa, respectively. The two-way interaction effects revealed significant (p<0.0001) variations in LWP due to shading by irrigation, shading by time of the day as well as irrigation by time of the day. Accordingly, coffee seedlings exposed to moisture deficits in full sun conditions exhibited minimum LWP on the 8th DAI, particularly in Harenna genotypes. Overall, the present findings demonstrated a two-fold advantage of shading coffee nurseries in optimizing water application and extending the occurrence of severe drought to damage coffee seedlings. However, the precipitation gradient of the geographical origins was not reflected in the LWP dynamics in coffee germplasm accessions, indicating the need for further research in understanding the underlying mechanisms involved in drought tolerance among the immense Arabica coffee genetic resources with the views to promote irrigated coffee farming and thus contribute to sustainable preservation and use of coffee gene pools at its original place of origin in Ethiopia.