Ex-situ Performance Evaluation of Coffee (Coffea arabica) Seedlings under Different Management Conditions: II. Root Growth Characteristics of Accessions.

Abstract

Root characteristics of coffee seedlings were studied with the main objective to compare the variations among twelve Coffea arabica germplasm accessions under contrasting nursery environments at Jimma Research Center, southwest Ethiopia.
Coffee seedlings from four wild coffee populations, namely, Harenna, Bonga, Berhane-Kontir and Yayu were ex-situ established under common nursery settings. The treatments included coffee germplasm accessions, shadings (moderate
shade and full sunlight) and irrigation levels (well-watered and water-stressed). One-year-old coffee seedlings were used to record root growth traits from five central seedlings per plot and the data were analyzed using SAS software. Coffee accessions significantly differed in most root characteristics. The longest and
shortest lateral roots were obtained from Yayu and Harenna seedlings, respectively. Berhane-Kontir accessions had significantly the lowest root volume as opposed to the highest value for the Harenna seedlings. Significantly higher root
dry biomass was obtained from unshaded than from shaded seedlings. The difference between watering regimes was also significant for root dry biomass and it was higher for water-stressed than for well-irrigated seedlings. Coffee accessions
were significantly differed in root proliferation and dry biomass and consequently, the lowest and highest average values were obtained from Berhane-Kontir and Harenna seedlings, respectively. The Harenna seedlings had a higher root mass
than the others, particularly the Berhane-Kontir accessions. The ratios of root to shoot dry biomass of the seedlings were significantly differed among coffee accessions, but not between shade and irrigation levels. The significantly lowest and highest root to shoot values was determined for the Berhane-Kontir and
Harenna accessions, respectively. Hence, Harenna genotypes can be considered as parents in coffee improvement programs under limiting water conditions.

Full text

Ethiop. J. Crop Sci. Vol. 3 No. 1 2013
48
Ex-situ Performance Evaluation of Coffee
(Coffea arabica) Seedlings under Different
Management Conditions: II.
Root Growth
Characteristics of Accessions
Taye Kufa and Alemseged Yilma
Ethiopian Institute of Agricultural Research,
Jimma Research Center, P.O.Box 192, Jimma
Abstract
Root characteristics of coffee seedlings were studied with the main objective to
compare the variations among twelve Coffea arabica germplasm accessions under
contrasting nursery environments at Jimma Research Center, southwest Ethiopia.
Coffee seedlings from four wild coffee populations, namely, Harenna, Bonga,
Berhane-Kontir and Yayu were ex-situ established under common nursery
settings. The treatments included coffee germplasm accessions, shadings (moderate
shade and full sunlight) and irrigation levels (well-watered and water-stressed).
One-year-old coffee seedlings were used to record root growth traits from five
central seedlings per plot and the data were analyzed using SAS software. Coffee
accessions significantly differed in most root characteristics. The longest and
shortest lateral roots were obtained from Yayu and Harenna seedlings,
respectively. Berhane-Kontir accessions had significantly the lowest root volume as
opposed to the highest value for the Harenna seedlings. Significantly higher root
dry biomass was obtained from unshaded than from shaded seedlings. The
difference between watering regimes was also significant for root dry biomass and
it was higher for water-stressed than for well-irrigated seedlings. Coffee accessions
were significantly differed in root proliferation and dry biomass and consequently,
the lowest and highest average values were obtained from Berhane-Kontir and
Harenna seedlings, respectively. The Harenna seedlings had a higher root mass
than the others, particularly the Berhane-Kontir accessions. The ratios of root to
shoot dry biomass of the seedlings were significantly differed among coffee
accessions, but not between shade and irrigation levels. The significantly lowest
and highest root to shoot values was determined for the Berhane-Kontir and
Harenna accessions, respectively. Hence, Harenna genotypes can be considered as
parents in coffee improvement programs under limiting water conditions.
Key Words: Coffee forest ecology; coffee diversity; moisture stress; natural resource
conservation; root growth characteristics

Ethiop. J. Crop Sci. Vol. 3 No. 1 2013
49
Introduction
The montane rainforests of Ethiopia
are the only known primary center of
origin and genetic diversity for the
highland arabica coffee (Coffea arabica
L.) species. Arabica coffee is thus a
shade adapted plant in the natural
multi-strata forest ecosystems with
the occurrence of wild Arabica coffee
populations (Wrigley 1988; Wintgens
2004). Ethiopia is endowed with
wide ecological suitability and
genetic potentials for sustainable
production and export of the finest
quality specialty coffee varieties and
natural forest grown coffees, while
conserving healthy forest
environments and promoting the
green economy development
strategy. According to Gole (2003)
and Bellachew and Sacko (2009),
however, coffee genetic resources of
Ethiopia are under continuous threat
of genetic erosions due to
deforestation and land degradation.
This coupled with the increasing
patterns of climate change are
endangering coffee environments
and diversity (Taye, 2006), requiring
urgent collaborative actions before
the situations reach an irreversible
stage to the global coffee sector.
In Ethiopia, there is immense genetic
diversity among and within wild
Arabica coffee populations, farmers’
domesticated coffee landraces and
released coffee varieties for
improvement of any desirable traits
such as high yielding, desirable
quality standard, disease resistance,
drought tolerance, low caffeine
content, etc. To date, a total of 6385
coffee germplasm collections are ex-
situ maintained and conserved at the
field genebanks of the Jimma
Research Center and its sub-centres
and sub-stations for research works.
Besides, there are also substantial
number of Arabica coffee collections
being conserved at the Institute of
Biodiversity field genebanks. This is
a unique genetic opportunity for the
future development of the coffee
sector and calls for strong national
and international cooperation to
support the complementary use of
both the in-situ and ex-situ
conservation approaches. This would
promote sustainable production and
marketing of best coffees, while
maintaining traceable quality profile.
Bellachew and Sacko (2006) pointed
out significant genotype by
environment interactions and the
need to adopt local landrace coffee
variety development program in
Ethiopia.
Root is the hidden plant growth part
that is equally important to the above
ground growth in the adaptation and
distribution of plant species, though
it is little studied and used in
perennial crops like coffee. Hence,
identificantion of ideal coffee
genotypes with desirable root traits is
important against the increasing
multifaceted challenges on arabica
coffee genetic resources in Ethiopia,
its birth place. The typical root

Ethiop. J. Crop Sci. Vol. 3 No. 1 2013
50
system of a mature Arabica coffee
tree consists of a taproot, axial
vertical roots; lateral roots, some of
which are more or less parallel to the
soil surface (surface plate roots) and
other deeper roots that ramify evenly
in the soil and sometimes become
vertical, feeder bearers evenly
distributed, and feeder-borne roots at
all depths (Wintgens, 2004). The
horizontal and vertical growth of
coffee roots can be influenced by
plant, environmental and soil factors.
This characteristic enables it to
exploit a considerable volume of land
and to thus offset a relative lack of
soil fertility condition. Coffee plant
requires an effective depth of greater
than 150 cm. Coffee trees can root
deeply in a normal soil although
about 90% of the roots develop in the
upper 30 cm soil layer. These roots
are sensitive to climatic variations
(temperature, drought and moisture),
but can be protected by shade and
mulch conditions (Wrigley, 1988).
Thus, root characteristics are
considered to play an important role
with regard to survival and better
performance of perennial crops like
coffee. Drought-adapted plants are
often characterized by deep and
vigorous root systems and according
to Daniel et al. (2004) total
transpiration was high in coffee
genotypes with relatively high root
biomass.
In Ethiopia, previous coffee research
focused on ex-situ characterization
and evalaution of the diverse coffee
collections, by considering largely
the shoot growth system. These
include yield and yield components,
resistance to diseases and insects,
quality attributes and tolerance to
drought environments (Girma et al.,
2008). Therefore, identification of
efficient accessions with respect to
ideal root traits is essential. The
existences of substantial inter- and
intra-genetic molecular diversity
(Kassahun, 2006) and morpho-
physiological growth natures (Taye,
2006) of wild arabica coffee
populations have been reported in
the natural coffee forests of Ethiopia.
The interplay between root and shoot
system depends on environmental
and plant factors, and the
physiological root to shoot behaviors
vis-à-vis plant age and
environmental influences remains to
be investigated. The impact of
changing climatic pattern and
declining soil fertility status can be
evidenced from the poor
performances of coffee trees, though
research information is scanty
especially on root growth natures of
coffee genetic resources under
different agro-ecologies and
production systems in Ethiopia.
In view of the huge genetic and
environmental opportunities and
progressive climate changes,
knowledge of below ground growth
traits is important in characterization,
evaluation and utilization of suitable
coffee cultivars. To this end,
investigations are necessary to assess
the underlying mechanisms and
identify drought-tolerant accessions

Ethiop. J. Crop Sci. Vol. 3 No. 1 2013
51
along varying amplitudes of
environmental stresses. This study
would provide insights into
understanding and identifying the
best genotype-environment
relationships and targeting
management options that contibute
to sustainable conservation and use
of coffee genetic resources in the
country. Thus, seedlings of arabica
coffee accessions were assessed
under varying sunlight and watering
conditions with the aim of
comparing the extent of variations in
root growth characteristics so that
future breeding program will be
targeted to identify drought tolerant
arabica coffee varieties for specific
agro-ecologies.
Material and Methods
The study area
The ex-situ experiment was
conducted in southwest Ethiopia, at
Jimma Research Center (JRC) (7°46’N
and 36° E). The center coordinates
the coffee research in the country
where national and international
coffee collections of about 6385 are
maintained with which various
breeding, agronomy and-soil-related
studies are undertaken. The center is
situated within the temperate to cool
humid highland agro-ecological zone
at an altitude of 1753 m.a.s.l. The area
receives a high amount of mean
annual rainfall (1556.88 mm) with
average maximum and minimum air
temperatures of 26.7 and 12.8°C,
respectively.
Experimental design and
Experimental design and Experimental design and
Experimental design and
treatments
treatments treatments
treatments
Fully ripe red cherries were
selectively collected from coffee trees
at three sites within four wild arabica
coffee populations; viz, Harenna,
Bonga, Berhane-Kontir and Yayu.
Except Harenna in the southeast, the
other three coffee forests are located
in the more humid southwest
Ethiopia (Table 1). Consequently,
coffee seedlings from a total of 12
accessions: Harenna (I-1, I-2, I-3),
Bonga (II-1, II-2, II-3), Berhane-Kontir
(III-1, III-2, III-3) and Yayu (IV-1, IV-
2, IV-3), were ex-situ established and
assessed under common nursery
settings at Jimma Research Centre in
2005. The potting medium was
prepared from blends of topsoil and
decomposed coffee husk compost at
the respective ratio of 3:1 (v/v) as
recommended by Taye et al. (2004).
Black plastic pots (volume = 5.8 liter)
were perforated at the bottom, firmly
filled with the growing medium and
arranged on seedbeds. Then, coffee
seeds were sown in each plastic pot
and all post-sowing nursery
operations were applied according to
the recommendations of the center
(Yacob et al., 1996). The coffee
seedlings were grown under optimal
nursery environments for about one-
year period until they attain
desirable growth stage to commence
the treatments.

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52
Table 1. Characteristics of the four montane rainforests where the study arabica coffee accessions
collected in Ethiopia
Variable
Harenna
Bonga
Berhane
-
Kontir
Yayu
Latitude (N)
6°23´
-
6°29´
7°17´
-
7°19´
7°04´
-
7°07´
8°23´
Longitude (E)
39°44´
-
39°45´
36°03´
-
36°13´
35°25´
-
35°26´
35°47´
Altitude (m a.s.l)
1420
-
1490
1520
-
1780
1040
-
1180
1400
Slop
e (%)
2
-
3
3
-
6
4
-
18
1
-
8
Rainfall
(mm/year)
950
1700
2100
1900
Max temperature (
o
C)
34.4
29.9
31.4
34.7
Min temperature (
o
C)
10.4
8.7
13.8
7.6
Mean temperature (
o
C)
22.2
18.2
20.3
19.7
Minimum RH (%)
37.9
45.0
50.8
41.8
Maximum RH (%)
84.3
95.2
85.4
98
.5
Mean RH (%)
63.2
80.4
68.9
80.9
Wind speed (m/ h)
0.93
0.64
0.43
0.35
Factorial combination of treatments
in a randomized complete block
design with three replications was
used to arrange the three main
treatments (shading, irrigation and
accessions). The experimental plots
were oriented in east to west
direction. The treatments included
shadings (moderate shade and full
sunlight), irrigation (well-watered
and water-stressed) and 12 coffee
germplasm accessions of varying
collection areas. The coffee seedlings
were maintained under controlled
contrasting shade environments for
eight months. Each treatment
consisted of 25 seedlings per plot.
Moderate (50% light interception)
overhead shade (2 m height) and side
shades were constructed from
uniform bamboo slants. Maximum
care was taken to avoid side-shading
effects between the treatments. For
this, the shade plots were far apart
from each other (12 m), while the
spacing between irrigation and coffee
accession plots was 2 m and 1 m,
respectively. The spacing between
coffee seedlings was increased with
ageing of the seedlings. At the
beginning, it was 10 cm x 10 cm and
later arranged at 20 cm x 20 cm
spacing. The water withheld plots
were covered with white plastic
sheet, whenever there is rain during
day and night times throughout the
study period. The diurnal
microclimate variables were
monitored during the study period
and the results depicted significant
differences between the shade
regimes (Taye, 2006). This depicts
that the treatment is enough to see
the variability among coffee genetic
accessions in root growth natures
due to the induced sub-optimal
water and sunlight stress
environments.
Root measurements
One-year-old seedlings were used to
record root growth traits of the
different arabica coffee accessions
under varying nursery management
conditions. For this, five central
seedlings per plot were used for root
measurements and the roots were
immersed and washed in water to

Ethiop. J. Crop Sci. Vol. 3 No. 1 2013
53
remove adhering soil. The most
important root growth parameters
(lateral root number, lateral root
length, taproot length, root volume)
were recorded for each independent
varaible. Subsequent to recording
root fresh weigt, each root part was
oven-dried at 105°C for 24 h and
weighed using a high sensitive
balance and other root growth
derivatives were determined.
Data analysis
Two-way analysis of variance
(ANOVA) was carried out using SAS
system for Windows version 8.1 (SAS
Institute Inc., Cary, NC) to see the
variations in seedling root growth
characters among arabica coffee
accessions under contrasting shade
and irrigation conditions. For any
significant results, the treatemt
means were compared according to
the Tukey‘s test at p = 5%. Finally,
the Pearson correlation matrix was
run between the most relevant root
triats.
Results
The number and volume of lateral
roots was comparable between shade
treatments, though the values were
higher for unshaded than for shaded
seedlings. Taproot and lateral roots
were slightly longer in the shade,
though not significantly different
from those of unshaded seedlings.
On the other hand, coffee accessions
significantly differed in total root
volume (P<0.001), taproot length
(P<0.05) and length of lateral roots
(P<0.01). The accessions, however,
did not differ in the number of lateral
roots, though the respective
maximum and minimum counts
were obtained from the Harenna and
Berhane-Kontir accessions. The
longest (19.19±0.45 cm) and shortest
(17.03±0.99 cm) lateral roots were
obtained from Yayu (IV-1) and
Harenna (I-3) seedlings, respectively.
Berhane-Kontir accessions had
significantly lowest root volume
(28.80±4.67 g cm
-3
) as opposed to the
highest value (48.50±2.78 g cm
-3
) for
the Harenna seedlings (Table 2).
A significantly (P<0.01) higher root
dry biomass was obtained from
unshaded than from partially shaded
seedlings, where a reduction of about
12% was noted. Similarly, higher dry
mass of leaf and total dry matter
were recorded for seedlings exposed
to direct sunlight than shaded plots
(Figure 1). The difference between
watering regimes was also significant
(P<0.01) for root dry mass and was
higher for water-stressed than for
well-irrigated seedlings. In the same
manner, coffee accessions
significantly differed (P<0.01) in root
dry mass and consequently, the
lowest (III-1 = 6.48 g) and highest (I-2
= 10.43 g) average values were
obtained from Berhane-Kontir and
Harenna seedlings, respectively
(Table 2).

Ethiop. J. Crop Sci. Vol. 3 No. 1 2013
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Table 2. Root growth parameters (means ± SD) in Arabica coffee seedlings according to shade, irrigation and accession treatments
Treatment RDW (g) RV (g cm-3) TRL (cm) LRN LRL (cm) R:S
RP (%)
Shading ** * * Ns Ns Ns Ns
Full sunlight
8.93±1.64
38.52±7.32
29.57±5.91
38.73±4.17
17.97±1.05
0.29±0.03
22.22±1.89
Partial shade
7.89±1.52
36.03±7.09
32.03±4.20
37.84±4.64
18.42±1.46
0.28±0.04
21
.45±2.81
Irrigation
**
Ns
***
*
Ns
Ns
Ns
Water stressed
8.90±1.52
36.36±6.03
33.68±4.90
39.52±4.00
18.42±1.19
0.29±0.03
22.35±2.02
Well
-
watered
7.92±1.66
38.18±8.31
27.91±3.80
37.05±4.48
17.98±1.35
0.27±0.04
21.33±2.68
Accession
**
***
*
Ns
*
**
**
I
-
1
10.02±1.11a
46.25±9.19ab
34.45±5.00
41.10±2.68
19.62±1.35
0.31±0.04ab
23.68±1.89ab
I
-
2
10.43±1.23a
48.50±2.78a
35.42±6.13
43.20±5.60
19.45±0.63
0.33±0.01a
24.82±0.87a
I
-
3
9.22±0.95ab
42.70±2.55abc
34.06±6.35
38.43±0.97
19.19±0.45
0.31±0.02ab
23.33±0.6
6ab
II
-
1
8.30±1.44abc
34.95±4.99cd
28.78±3.76
39.25±7.93
17.07±0.97
0.28±0.02abc
21.48±1.19abc
II
-
2
7.97±1.11abc
35.25±5.54bcd
31.74±5.06
39.70±3.50
17.77±0.77
0.28±0.03abc
22.16±1.45abc
II
-
3
8.15±1.34abc
37.55±4.35a
-
d
30.71±6.20
36.58±1.83
19.16±0.61
0
.29±0.04abc
22.37±2.04abc
III
-
1
6.48±1.09c
32.70±5.13cd
27.38±4.15
33.08±3.74
17.99±1.18
0.25±0.04 bc
19.50±3.15bc
III
-
2
7.22±1.66bc
31.20±4.98d
28.73±4.53
36.50±4.89
18.11±1.41
0.27±0.04abc
20.75±2.89abc
III
-
3
6.86±1.20bc
28.80±4.67d
27.39±6.56
36.60±2
.15
17.31±0.91
0.23±0.03c
18.34±1.86c
IV
-
1
8.67±0.30abc
37.25±4.33a
-
d
27.14±2.74
38.15±4.83
17.03±0.99
0.28±0.02abc
21.88±1.32abc
IV
-
2
9.39±1.00ab
38.65±3.22a
-
d
30.58±1.25
39.75±2.71
18.38±1.34
0.29±0.01abc
22.39±0.92abc
IV
-
3
8.23±2.43abc
33.45±4.89cd
3
3.21±5.18
37.10±3.19
17.32±1.03
0.27±0.05abc
21.38±2.81abc
Mean
8.41
37.27
30.80
38.29
18.20
0.28
21.84
CV (%)
10.72
10.61
10.38
9.77
5.05
9.31
7.67
Ns = Not significant; *, ** and *** = significant at P<0.05, P<0.01 and P<0.001, respectively. Means followed by same letter with in a column are not different from each other (Tukey‘s
test at P = 0.05). Abbreviations: RDW= root dry weight, RV = root volume, TRL = taproot length, LRL = lateral root length, R:S = root to shoot ratio, RP = root partitioning.

Ethiop. J. Crop Sci. Vol. 3 No. 1 2013
55
I-1 I-2 I- 3 II-1 II-2 II-3 III-1 II I-2 I II-3IV- 1IV -2IV-3
Root dry mass (g)
0
2
4
6
8
10
12
14
16
Su n
Sh ad e
Leaf dry mass (g)
0
2
4
6
8
10
12
14
16
18
20
Su n
Shad e
Total dry mass (g)
0
10
20
30
40
50
60
Su n
Shad e
I-1 I -2 I- 3 II- 1 II-2 II- 3 II I-1 II I-2 II I-3 IV -1IV -2 IV-3
Root : shoot
0.0
0.1
0.2
0.3
0.4
0.5
Su n
Shad e
Figure 1.Biomass yield and root to shoot ratio of Arabica coffee accessions under full sun and shaded conditions
In general, the Harenna seedlings
had a higher root mass than the other
coffee genotypes, particularly the
Berhane-Kontir accessions, which
had a low root biomass ranging
between 6.48 and 7.22 g. This was
less than the overall average root dry
biomass of 8.41 g. The ratios of root
to shoot dry mass of the seedlings
were also significantly differed
among the accessions, but not
between shade and irrigation levels.
Though insignificant, the amount of
total dry mass partitioned to the root
part was higher in full sunlight and
water-stressed seedlings as
compared to the lower shares in
partial shading and well-watered
seedlings. The coffee accessions from
Berhane-Kontir had significantly
(P<0.01) the lowest (18.3%) root
partitioning as compared to the
Harenna seedlings, which had the
highest (38.6%) root share. However,
root to shoot ratio of some seedlings
surpassed those in shadow
conditions. The significantly lowest
(III-3 = 0.23) and highest (I-2 = 0.33)
root to shoot values were determined
for the Berhane-Kontir and Harenna
accessions, respectively (Figure 2). As
a whole, root to shoot ratio was
higher for the other accessions from
Harenna than those from Berhane-
Kontir. In addition, there were
positive and significant associations
between most root and shoot growth
characteristics of coffee seedlings
(Table 3), and stem and root dry
weights were equally and
significantly (r = 0.96**) correlated to
total biomass yield. Moreover, leaf
dry matter was significantly
associated with root biomass (r =
0.71**) and total dry matter (r =
0.85**), indicating the role of leaves
in carbon assimilation and
distribution to different plant parts in
coffee seedlings.

Ethiop. J. Crop Sci. Vol. 3 No. 1 2013
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Table 3. Pearson correlation between root parameters in seedlings of arabica coffee genotypes
Parameter
RFW
RDW
RV
TRL
LRN
LRL RS
RDW
0.94**
RV
0.99**
0.92*
TRL
0.51
0.53
0.51
LRN
0.74*
*
0.79**
0.73**
0.73**
LRL
0.81**
0.73**
0.81**
0.32
0.51
RS
0.82**
0.73**
0.84**
0.46
0.75**
0.70*
*, ** = Correlations are significant at 0.05 and 0.01 levels, respectively (2-tailed). For abbreviation see Table 1
above.
Dry mass in sun (g)
0
1 0
2 0
3 0
4 0
5 0
C o f fe e a c c e s si o n
I - 1 I - 2 I - 3 II - 1 I I- 2 I I - 3 I I I - 1 I I I - 2 I II - 3 I V - 1 IV - 2 IV - 3
Dry mass in shade (g)
0
1 0
2 0
3 0
4 0
5 0
R o o t
S h o o t
Figure 2. Root and shoot dry mass for seedlings of arabica coffee accessions under (a) full sunlight and (b) shaded
nursery conditions
Discussion
The longest and shortest lateral roots
were obtained from Yayu and
Harenna seedlings, respectively.
Berhane-Kontir accessions had
significantly lowest root volume as
opposed to the highest value for the
Harenna seedlings. This reflects that
coffee saplings can adapt to drought
situations by extending the root
system into deeper soil layers. The
correlations between root growth
parameters and root hydraulic
resistance were strong and indirect in
well-irrigated coffee seedlings, i.e.,
seedlings with better root systems
showed significantly higher root
hydraulic conductance and were
more productive in terms of biomass
production (Burkhardt et al., 2006)
and hydraulic conductance patterns
under field conditions (Taye and
Burkhardt, 2010). This was observed
in the direct sunlight exposed
seedlings and Harenna accessions.
Thus, the results obtained provide
information on the closeness of shoot
and root physiological events under
drought-stress environments, which
ultimately lead to the control of
transpiration water loss and total dry

Ethiop. J. Crop Sci. Vol. 3 No. 1 2013
57
matter distribution patterns. To this
end, several studies (Yacob et al.,
1996; Pinheiro et al., 2005) showed
correlations between morphological
and yield components. The
knowledge of the correlation is
invaluable to the breeder in selecting
desirable morphological traits. In this
study, simple correlation was
computed between morphological
parameters, which showed a
different magnitude of relationships.
The influence of irradiance was not
significant on root growth response,
perhaps due to the limited time for
the shade treatment to bring about
differences. Nevertheless, full
sunlight exposed seedlings had a
slightly higher number and volume
of lateral roots. In contrast, a longer
taproot and lateral roots were
observed for shaded seedlings than
unshaded ones. This indicates the
influence of short-term drought
stress in affecting root growth. On
the other hand, there were significant
differences among the coffee
accessions in total root volume,
taproot length and length of lateral
roots. Root morphological
parameters were significantly highest
for Harenna as opposed to the lowest
values obtained from the Berhane-
Kontir accessions. Similar to shoot,
the Yayu and Bonga accessions were
intermediate in root growth. The
higher lateral root count and volume
in full sun seedlings were in line with
the root dry weight and root to shoot
ratio recorded on the same coffee
seedlings. This could be an indicative
of high root access to maximize soil
water uptake in limited soil-water
conditions. Hence, the significantly
better root growth in the Harenna
accessions could be related to their
soil moisture-stress avoidance
mechanism as compared to the
southwest origin coffee accessions.
The amount of total dry mass
partitioned to the root part was
higher in full sunlight and water
stressed seedlings as compared to
those under shading and well-
watered seedlings. This corresponds
with the more luxurious shoot
growth of coffee seedlings at
resource rich environments as
opposed to deep root systems in
drought situations, indicating the
influence of genetic, climate and soil
conditions.
The coffee accessions from Berhane-
Kontir had highly significantly
lowest root partitioning as compared
to the Harenna seedlings, which had
the highest root share (Taye, 2006).
The present root growth performance
is in consistent with the variations in
the shoot growth response of the
same coffee accessions (Taye et al.,
2004), indicating the interplay
between root and shoot growth
system. According to Taye (2006), the
coffee accessions were grouped into
three broad dissimilarity classes. The
first cluster consisted of a mixture of
accessions from Yayu, Bonga,
Berhane-Kontir and Harenna,
whereas the Bonga and Harenna
accessions were classified into the
second and the third cluster,

Ethiop. J. Crop Sci. Vol. 3 No. 1 2013
58
reflecting the similarity within the
two wild coffee forest units.
Kassahun (2006) also found inter-
and intra-genetic molecular diversity
in the same wild coffee populations.
Coffee accessions from the driest site,
Harenna, showed highest
conductance, largely due to their
extensive root system, high
transpiration and biomass
production (Burkhardt et al., 2006).
However, these were most
vulnerable and they failed to
withstand under persisting moisture
deficits as opposed to others,
especially the Bonga and Berhane-
Kontir accessions. The same findings
demonstrated that the southeastern
and southwestern coffee germplasm
accessions were found to follow
opportunistic and conservative ways
of water use strategies, respectively.
The substantial variations in root
growth characteristics are in
agreement with the findings under
field conditions (Kufa and
Burkhardt, 2011), indicating the
consistency of root traits and in part
underlined the diversity in
adaptation mechanisms as pointed
out by Sobrado (2003).
Conclusion
The present study assessed the
influence of varying nursery
management practices on seedling
root growth response of wild coffee
genotypes. Early stage root traits
were significantly different due to
coffee accessions. This may
demonstrate the more influence of
genetic as compared with
environmental factors. Harenna
accessions had ideal root
characteristics and performed better
under limited soil moisture
conditions and these genotypes
could be used as desirable parents in
coffee improvement programs. Root
characteristics can be used to identify
suitable coffee genotypes for specific
climate and soil conditions. In view
of the current climate variability and
change, it is also essential to
understand drought tolerant coffee
cultivars with efficient water use
efficiency and to target effective
management options under varying
agro-ecologies and production
systems. The variation in root growth
response was substantial among
accessions of distant geographical
areas, possibly due to coffee genetic
diversity and water use efficiency in
arabica coffee genotypes. The
findings also contribute to promote
sustainable conservation,
management and use of arabica
coffee genetic resources and its shade
environments in Ethiopia.
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