Eco-physiological basis of drought stress in coffee (Coffea arabica, L.) in Ethiopia

Abstract

Drought and unfavorable temperatures are the major climatic limitations for coffee production in Ethiopia. These limitations are expected to become increasingly important in several coffee growing areas and are the main factors responsible for the fluctuations in coffee yield. Because of population pressure for arable lands in most of coffee growing areas in Ethiopia, coffee cultivation has spread towards marginal areas where water shortage and high temperature constitute significant reduction in coffee yield. Also, in most cases, there is shortage of water resources for irrigation during prolonged dry spells which affect the growth and the development of plants under different forms during the phonological phases of the coffee crop. Such environmental factors include reduced rainfall and high temperatures both of which majorly contribute to drought. Arabica coffee (Coffea arabica, L.) is a shade adapted plant in the natural multi-strata forest ecosystems with the occurrence of wild Arabica coffee populations in Ethiopia. However, these are fragmented forests and their coverage is shrinking from time to time, largely due to anthropogenic activities. As a result, coffee is either replaced by other crops or its cultivation is expanding into less suitable open-sun conditions. These coupled with the increasing patterns of climate change are threatening coffee production of the country, as well as the natural gene pools of Arabic coffee. Coffee genetic resources are believed to possess desirable traits, including high yielding, superior quality, resistance to diseases, tolerant to moisture stress and other important agronomic traits. Nonetheless, the underlying adaptation strategies that take into account genetic and environmental factors remain little understood to fully exploit the wealth of coffee and ecological diversity in Ethiopia. Because released Arabica coffee varieties and landraces in Ethiopia can be broadly classified into three canopy classes of open, medium and compact crown types and their water relations can vary accordingly. To this end, information on eco-physiological traits (genetically fixed traits) of coffee towards identifying drought tolerant Arabica coffee cultivars for specific geographical areas is very crucial and would also help in predicting the future field performances of coffee genotypes under varying environmental conditions. Agronomic measures against drought control, such as shading, irrigation, high density planting and use of resistant genotypes that are adapted to climatic fluctuations are also the alternative solutions against drought tolerance in coffee cultivation. In this review we highlighted some aspects of drought stresses on coffee growth and development in addition to focusing our attention on eco-physiology of production in Arabica coffee under Ethiopian coffee growing situations. The review is organized into sections dealing with: (i) coffee plant traits involved in drought tolerance, (ii) physiological approaches to determine drought tolerance (iii) findings in drought adaptation of Arabica coffee in Ethiopia, (iv) photosynthesis and crop yield, (v) In-situ Eco-physiological response to natural drought, (vi) agronomic methods for controlling drought stress and, (vii) impact and responses of coffee plant to drought stress.