Deep rooting ability is identified as an important trait for drought resistance in Canavalia brasiliensis, a forage legume. The study tested the hypothesis that C. brasiliensis' superior tolerance of long dry seasons under low soil fertility is related to its deep rooting ability. Using a greenhouse method, the study found that genotypes CIAT 7969 and CIAT 905 produced more leaf area under both fertilized and drought conditions, indicating drought tolerance, while genotype CIAT 21014 produced less leaf area. Genotype CIAT 905 also showed lower leaf conductance under drought stress, regulating water loss. Rooting depth measurements found genotypes CIAT 7969 and CIAT 905 developed deeper root systems than

1. Deep rooting ability is identified as an important trait for drought
resistance in Canavalia brasiliensis, a forage legume
J. Polanía1, S. Douxchamps2, A. Oberson2, E. Frossard2, R. Van der Hoek1, L. Franco1, M. Peters1 and I. Rao1
1International Center for Tropical Agriculture (CIAT), A.A. 6713, Cali, Colombia
2Institute of Plant Sciences, ETH-Zurich, Switzerland
E-mail: j.a.polania@cgiar.org; i.rao@cgiar.org
Introduction The genotypes CIAT 7969 and CIAT 905 were outstanding
in leaf area production under both fertilizer and water
In some forage legumes such as Stylosanthes guianensis,
drought avoidance is linked with deep rooting ability that
Canavalia brasiliensis (Figure 1), a highly drought adapted regimes. The genotype Canavalia sp. CIAT 21014 showed contribute to improved acquisition of water and nutrients
cover legume (stays green during 5 months of dry season), lower values of leaf area under both fertilizer and water leading to superior dry season tolerance. Similar
native from Central America; was introduced into the regimes. mechanism was observed in canavalia.
smallholder’s traditional crop-livestock production system
The genotype CIAT 905 showed the lower value of leaf
of the Nicaraguan hillsides to overcome soil fertility
conductance under individual drought stress conditions (high A B
decline. Canavalia increases available forage biomass
fertilizer + terminal drought) and combined low fertility
and augments milk production in the dry season
and drought stress indicating the ability to regulate
(Douxchamps et al, 2008).
transpirational waterloss .
There is very limited knowledge on the physiological basis 0
Canavalia b. CIAT 17009 Canavalia b. CIAT 7969
of adaptation of Cavavalia to either individual or
combined stress factors of drought and low soil fertility. 20
We tested the hypothesis that the superior tolerance of
40
canavalia to long dry season under low soil fertility
Rooting depth (cm)
conditions is related to its deep rooting ability. We used a 60
greenhouse soil tube method to quantify phenotypic
differences in root development and distribution of 4 80
germplasm accessions of canavalia under simulated soil 0
Canavalia b. CIAT 905 Canavalia sp. CIAT 21014
drying (terminal drought) combined with low fertilizer
application. 20
Figure 4. Influence of high fertilizer application combined
40 with drought stress and irrigated conditions (A) and no
fertilizer application combined with drought stress and
60 Irrigated + high fertilizer irrigated conditions (B) on root development of Canavalia
rooting depth
Irrigated + without fertilizer
Drought + high fertilizer CIAT 905
Drought + without fertilizer
80
0 10 20 30 40 0 10 20 30 40
Days after planting A B
Figure 2. Influence of individual and combined stress
factors of drought and low soil fertility on deep rooting of
4 Canavalia genotypes that were grown under
greenhouse conditions of CIAT, Palmira
High fertilizer application
80
Irrigated Terminal drought
LSD 0.05: 8.7
LSD 0.05: NS
60
40
Total root length (m plant )
-1
20
Figure 1. Pod, seed, twining foliage, trifoliolate leaves
0
and inflorescence of Canavalia brasiliensis Mart. ex Benth. T7
969 T9
05
T1
700
9
T2
101
4
T9
05
T7
9 69
T1
70 0
9
T2
10 1
4
CIA CIA CIA CIA CIA CIA
CIA CIA
Without fertilizer application Figure 5. Influence of high fertilizer application combined
80
Irrigated Terminal drought with drought stress and irrigated conditions (A) and no
Materials and Methods 60 LSD0.05: 9.6
LSD0.05: NS fertilizer application combined with drought stress and
irrigated conditions (B) on root development of Canavalia
40 CIAT 7969
A greenhouse study was conducted at CIAT-Palmira in
2009 using a mix of an Andisol (from Darien of
20 Conclusions
Colombia) with river sand (2:1 w/w). Plants were grown 0
9 4
T9
05 9 69 7 00
9
1 01
4 969 T9
05 700 101
T7 T7
for 35 days in plastic cylinders (80 cm long with 7.5 cm CIA CIA CIA
T1
CIA
T2
Genotype
CIA CIA CIA
T1
CIA
T2
Results from this greenhouse study indicated that drought
diameter) that were inserted in PVC tubes. The trial
resistance of canavalia under low soil fertility conditions is
included 4 canavalia genotypes: Canavalia brasiliensis Figure 3. Influence of individual and combined stress of low
CIAT 17009, Canavalia brasiliensis CIAT 905, Canavalia soil fertility and drought on total root length of 4 associated with deep rooting ability and vigorous fine
brasiliensis CIAT 7969 and Canavalia sp. CIAT 21014. Canavalia genotypes that were grown under greenhouse root development to explore greater volume of soil. Two
The trial was planted as a randomized complete block conditions of CIAT, Palmira Canavalia brasiliensis accessions (CIAT 7969 and CIAT
arrangement with two levels of water supply: well- Genotypic differences were observed in deep rooting 905) were found outstanding in their total root length
watered and terminal drought stress conditions, and two ability among treatments. All the genotypes, except CIAT production across soil depth under combined stress factors
levels of fertilizer application to soil: high amounts of 21014, showed a greater deep rooting ability under
fertilizer application and without fertilizer application. of low soil fertility and drought.
individual drought stress and combined stress of drought
A number of shoot traits were measured during the
and low soil fertility (Figure 2). The genotypes CIAT 17009
and CIAT 7969 were outstanding in their deep rooting References
experiment, including total chlorophyll content (SPAD), ability under individual low soil fertility conditions. The Douxchamps S., R. Van der Hoek, A. Benavidez, F.
photosynthetic efficiency, leaf conductance and rooting genotypes CIAT 17009 and CIAT 7969 showed greater Humbert,M. Mena, A. Oberson, I.M. Rao, A. Schmidt and E.
depth. At harvest time (35 days after planting; 27 days ability for deep rooting under drought conditions with or Frossard. 2008. Realizing the benefits of cover crop
with water stress treatment), leaf area, shoot biomass without fertilizer application (Figure 2). legumes in smallholder crop-livestock farms of the hillsides
distribution, and root traits (root length, mean root
The genotypes CIAT 905 and CIAT 7969 were superior in of Central America. Poster presented at the Annual
diameter, specific root length, and root dry weight)
root length production under individual terminal drought Conference 2008. North-South Centre Research for
were determined.
Development. ETH, Switzerland
Results conditions and individual low soil fertility conditions (Figure
3). The genotypes CIAT 905 (Figure 4) and CIAT 7969
During the plant growth and development the maximum
(Figure 5) were outstanding in their total root length
production across soil depth under combined stress of
Acknowledgements
and minimum air temperatures were 33 and 21 oC. The This work is partially supported by funds from SDC-ZIL,
drought and low soil fertility.
final soil moisture under terminal drought stress was at 8% Switzerland
of the field capacity.