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International Research Journal of Agricultural Science and Soil Science (ISSN: 2251-0044) Vol. 2(12) pp. 498-
501, December 2012
Available online http://www.interesjournals.org/IRJAS
Copyright ©2012 International Research Journals
Review
Drought and heat tolerance in coffee: a review
Cheserek J.J.* and Gichimu B.M
Coffee Research Foundation, P.O. Box 4 – 00232, Ruiru, Kenya
Abstract
Climatic variability is the main factor responsible for the fluctuations in the coffee yield in the world.
The relationships between the climatic parameters and the agricultural production are quite complex,
because environmental factors affect the growth and the development of plants under different forms
during the phenological phases of the coffee crop. Such environmental factors include reduced rainfall
and high temperatures both of which majorly contribute to drought. This paper briefly reviews some of
the important aspects of drought and heat tolerance in coffee. It highlights the impacts of draught and
high temperatures in coffee production, tolerance mechanisms, necessary interventions, selection
challenges and current advances towards development of drought and heat tolerant coffee cultivars.
Keywords: Coffee, Water Stress, High Temperatures, Tolerance Mechanisms.
INTRODUCTION
Among some 90 species of the genus Coffea, C. arabica
L. (Arabica coffee) and C. canephora Pierre (Robusta
coffee) economically dominate the world coffee trade,
being responsible for about 99% of world bean
production (Da Matta and Ramalho, 2006). Arabica
coffee accounts for more than 62% of the world coffee
production (Dias et al., 2007) and 90% of the world coffee
market (Worku and Astatkie, 2010). Robusta coffee
accounts for the rest. Compared with Arabica, Robusta
coffee generally appears to be more vigorous, productive
and robust, but the quality of the beverage derived from
its beans is considerably inferior to that from Arabica
(Coste, 1992; Da Matta and Ramalho 2006).
Drought is an environmental factor that causes water
deficit or water stress in plants (Pinheiro et al., 2005).
Overall, drought and unfavourable temperatures are the
major climatic limitations for coffee production (Da Matta
and Ramalho 2006). These limitations are expected to
become increasingly important in several coffee growing
regions due to the recognized changes in global climate
and also because coffee cultivation has spread towards
marginal lands, where water shortage and unfavourable
temperatures constitute major constraints to coffee yield
(Da Matta and Ramalho 2006; Kimemia, 2010). The
global warming caused by increase of greenhouse gas
emissions (carbon dioxide and methane) in the
*Corresponding Author E-mail: cheserekjerono@yahoo.com
atmosphere is causing wide changes in atmospheric
events resulting to climate change. These include,
shifting of optimal growing zones, changes in rainfall
(amount and distribution), and changes in dynamics of
crop diseases and pests, loss of agricultural land due to
either rising sea levels and/or desertification (Kimemia,
2010). The combined effects of this phenomenon have
critical impacts on coffee production.
Many reviews focusing on the morphology and
physiology of both Arabica and Robusta coffee with
respect to drought and extreme temperatures (Barros et
al., 1999; Carr, 2001; Maestri et al., 2001; DaMatta and
Rena, 2001, 2002; DaMatta, 2004 and DaMatta and
Ramalho, 2006) have been published. The present
review is mainly focused on impact of draught and high
temperatures on coffee production and necessary
interventions related to crop improvement. It therefore
highlights some morphological and physiological
traits/mechanisms which are important in selecting
drought and heat tolerant coffee genotypes. It further
focuses on selection challenges and current advances
towards development of tolerant genotypes.
Impacts of drought and high temperatures on coffee
production
Coffee is indigenous to African regions characterized by
abundantly distributed rainfall and atmospheric humidity
frequently approaching saturation (Pinheiro et al., 2005).
For this reason, coffee probably evolved as ‘water-
spender’ species (DaMatta and Rena, 2001). Coffee is
therefore a highly environmentally-dependent crop and
an increase of a few degrees of average temperature
and/or short periods of drought in coffee-growing regions
can substantially decrease yields of quality coffees.
Taking into account the global warming phenomena,
severe reductions of adequate coffee growing areas are
to be expected (DaMatta and Ramalho, 2006) thus
sustainability of coffee productivity and quality may
become more difficult to maintain. Experts warn that
temperature may rise up to 5.8°C in the tropical area by
the end of the 21st century (Camargo, 2009). In Kenya,
climate change has rendered a significant proportion of
traditional coffee growing zone less suitable for coffee
production. This has caused shifting from optimal to sub-
optimal and marginal growing zones, resulting in changes
in crop yields and quality. In Uganda, severe impacts of
climate change on coffee production are expected as
temperature rise by 2ºC in the next few decades
(Kimemia, 2010). In Brazil, Robusta coffee is currently
largely cultivated in regions where water availability
constitutes the major environmental constraint affecting
crop production (Pinheiro et al., 2005).
Extreme temperatures, depending on their intensity,
duration and speed of imposition, impair cell metabolic
processes (e.g. photosynthesis), growth and survival of
plants, as well as their economic exploitation (DaMatta
and Ramalho, 2006). In fact, temperature may limit the
successful economic exploitation of the coffee crop, in
part because coffee growth is particularly affected by
both high and low temperatures (Barros et al., 1997; Silva
et al., 2004). The optimum mean annual temperature
range for Arabica coffee is 18-21ºC (DaMatta and
Ramalho, 2006). Above 23ºC, development and ripening
of fruits are accelerated, often leading to loss of quality
(Camargo, 2009). Continuous exposure to temperatures
as high as 30ºC could result in not only depressed growth
but also in abnormalities such as yellowing of leaves and
growth of tumors at the base of the stem (DaMatta and
Ramalho, 2006). A relatively high temperature during
blossoming, especially if associated with a prolonged dry
season, may cause abortion of flowers (Camargo, 2009).
In addition, large variations in temperature also increase
bean defects, modify bean biochemical composition and
the final quality of the beverage (Carr, 2001; Silva et al.,
2005). For Robusta coffee, the optimum annual mean
temperature ranges from 22 to 30ºC (DaMatta and
Ramalho, 2006). Robusta coffee can be grown between
sea level and 800 m, whereas Arabica coffee grows best
at higher altitudes and is often grown in hilly areas, as in
Colombia and Central America (Baker and Haggar 2007).
In Kenya, the main coffee growing areas ranges from low
to high altitude (1200 m to over 1700 m above sea level)
(Kimemia, 2010; Gichimu 2012).
Cheserek and Gichimu 499
Drought and heat tolerance mechanisms
For cultivated plants, tolerance to drought is generally
considered as the potential for a particular species or
variety to yield more in comparison to others under
limited soil water conditions (Pinheiro, 2004). A
complementary approach to improve plant performance
for drought-prone regions involves the identification and
selection of traits that contribute to drought tolerance. A
partial list of potentially important traits might include
water-extraction efficiency, water-use efficiency (WUE),
hydraulic conductance, osmotic and elastic adjustments,
and modulation of leaf area. Most of these traits are
complex and their control and molecular basis is not well
understood (Da Matta, 2004). However, species/varieties
more tolerant to drought generally differ morphologically
and/or physiologically with mechanisms that allow them
to produce comparable yield under limited water supply
(Da Matta, 2004). Examples include maximization in
water uptake by growing deep roots and/or minimization
of water loss by way of an effective stomatal closure and
reduced leaf area thus improving plant water status and
turgor maintenance (Kufa and Burkhardt, 2011; Kramer
and Boyer, 1995). Turgor maintenance, which provides
the potential for keeping physiological activity for
extended periods of drought, may be achieved through
an osmotic adjustment and/or changes in cell wall
elasticity (Kramer and Boyer, 1995; Turner 1997).
Like many plant species, coffee displays a diversity of
acclimation mechanisms to avoid and endure drought
and heat stresses (as well as the oxidative stress usually
promoted by them), developed within the genetic bounds
of the plant/species (Da Matta and Ramalho, 2006;
Worku and Astatkie, 2010). When working with potted
plants, Pinheiro et al., (2005) found out that plant water
stress develops more slowly in the drought-tolerant than
in the drought-sensitive clones. Morphological traits such
as leaf area and root mass to leaf area ratio were not
associated with that response. Instead, the much deeper
root system of the tolerant clones enabled them to gain
greater access to water towards the bottom of the pots
and, therefore, to maintain a more favourable internal
water status longer than in drought-sensitive clones. Root
characteristics and growth play a crucial role in
maintaining the water supply to the plant, and drought
adapted plants are often characterized by deep and
vigorous root systems (Blum, 2005). However, Burkhardt
et al., (2006) observed coffee plants with extensive root
system but vulnerable to drought due to their hydraulic
system and stomatal behavior.
Physiological evaluations of some of the coffee clones
perceived to be drought tolerant suggested that keeping
an adequate water status, maintenance of leaf area (Da
Matta et al., 2003; Pinheiro et al., 2005), and steep leaf
inclinations (Pinheiro and DaMatta, unpublished results),
500 Int. Res. J. Agric. Sci. Soil Sci.
are of utmost importance. Biochemical traits such as
improved tolerance of oxidative stress (Lima et al., 2002;
Pinheiro et al., 2004) and ability to maintain assimilate
export (Praxedes et al., 2005) are also considered
important. Drought-tolerant coffee genotypes are able to
maintain higher tissue water potential and water use
efficiency than drought-sensitive ones under water-deficit
conditions (DaMatta, 2004; Dias et al., 2007). Such
differences are even more evident in the field, where the
development of the root system is much less restricted
(Da Matta et al., 2003). When comparing the yields of
drought-tolerant and drought-sensitive clones, Da
Matta et al., (2003) found that the better crop yield of the
drought-tolerant clone was associated with maintenance
of leaf area and higher tissue water potentials, as a
consequence of smaller stomatal conductance, which
would result in less carbon isotope discrimination.
Combining traits associated with a favourable water
status and suitable biochemical characteristics, which
enable some degree of tissue tolerance to desiccation,
should improve coffee yields over a range of drought
conditions. However, most of these traits do not appear
to be well developed in drought-tolerant clones which
favour survival over productivity under drought
conditions.
Different species of coffee (e.g. Arabica and Robusta)
may also differ in morphological and/or physiological
mechanisms that allow them to produce considerably well
under limited water supply (Da Matta, 2004). Arabica
coffee genotypes have been found to differ in drought
adaptation mechanisms such as stomata control and soil
water extraction efficiency (DaMatta and Ramalho, 2006),
plant water use and biomass allocation to the stems and
leaves (Dias et al., 2007) and tissue water potential
(DaMatta, 2004). On the other hand, studies on Robusta
coffee showed deeper root system (Pinheiro et al., 2005)
and larger root dry mass in drought tolerant clones than
in drought sensitive ones (DaMatta and Ramalho, 2006).
Further, Lima et al. (2002) proposed that drought
tolerance in Robusta coffee might, at least in part, be
associated with enhanced activity of antioxidant enzymes
although Pinheiro et al., (2004) did not corroborate these
findings. The efficiency of all these mechanisms will
determine the ability to cope with such environmental
conditions, thus setting limits to species/genotypes
distribution.
Necessary interventions and selection challenges
Researchers are being challenged to be better prepared
by breeding varieties that will cope with the impacts of
drought or high temperatures (Motha, 2008) and
repackage and promote climate change mitigation
strategies (Smith et al., 2008; Kimemia, 2010).
Identification of coffee genotypes that could withstand
drought spells with acceptable yields should be the first
requirement for a successful breeding programme for
drought tolerance. Considering the fast changing climate,
drought tolerant genotypes must also have good
combining abilities for yield, diseases and quality. Under
low-input conditions typical of many farming systems of
drought-prone regions, cultivars with better yield stability
under drought stress, or better able to survive drought
episodes, may be of greater value than cultivars with high
yield potential selected for improved environments.
However, despite all the efforts applied towards
understanding drought tolerance in coffee, there is no
consistent information about the causes of the
differences in drought tolerance in coffee. According to
Blum (2005) the conceptual framework of what actually
constitutes a viable target for selection in respect to
drought tolerance is not always clear. For Arabica coffee,
additional challenge is that of low genetic variation
available within the genome and its close relatives forcing
the breeders to look further afield.
Current advances
In some countries, research on developing drought
tolerant coffee varieties for climate change adaptation
has started. In Brazil plant breeders have registered
considerable success in selecting some promising
Robusta clones with relatively high bean yields and low
year-to-year variation of bean production under rain-fed
conditions. The selection has been largely empirical as
al., information about how coffee responds
physiologically to drying soil is still unclear (Pinheiro et
al., 2005; Da Matta and Ramalho 2006). In Kenya and
Uganda, basic research is ongoing whereby coffee
genotypes are being subjected to drought and heat stress
by denying them sufficient water in a greenhouse to
detect and select those that are tolerant. The genotypes
will then be tried in hot and dry areas. Some Arabica
coffee genotypes that are known to have some drought
tolerance attributes include Tanganyika Drought resistant
genotypes DR I and DR II (Trench, unpublished), and
Indian cultivar Sln 9 (D'Souza 2009). Such genotypes
could be exploited in future drought tolerance breeding
programmes.
CONCLUSION
This review enabled better understanding of the different
ways in which coffee adapts to drought and heat
tolerance. It further highlighted some morphological and
physiological traits which are important in selecting
drought and heat tolerant coffee genotypes. These facts
will guide the ongoing and future trials on heat and
drought tolerance in coffee.
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