Phenotypic differences in root development and distribution among 97
recombinant inbred lines (RILs) of DOR 364 x BAT 477 under drought stress
Jose A. Polania, Asrat Asfaw, Steve Beebe, Matthew Blair and Idupulapati M. Rao
International Center for Tropical Agriculture (CIAT), A.A. 6713, Cali, Colombia
E-mail: firstname.lastname@example.org; email@example.com
Introduction Table 1. Correlation coefficients (r) between grain yield (kg/ha-
Drought is the major abiotic constraint affecting common bean field) and root traits (greenhouse) in RILs of the cross DOR 364
(Phaseolus vulgaris L.) production. About 60% of the bean x BAT 477. *, **, *** Significant at the 0.05, 0.01 and 0.001
crop is cultivated under the risk of either intermittent or probability levels, respectively.
terminal drought (Beebe at al., 2008, White and Singh,
1991). The effects of drought on common bean are Root traits Irrigated Rainfed
dependent on the intensity, type and duration of the stress. Total root length (m plant-1) 0.04 0.12*
Development of drought adapted bean varieties is a logical Mean root diameter (mm) 0.12* 0.14*
choice to minimize crop failure and improve food security in
bean growing regions (Rao, 2002). Previous research Root volume (cm3) 0.07 0.17**
suggested that drought avoidance by increasing extraction of Deep rooting at 35 dap (cm) 0.11 0.17**
soil moisture is an important mechanism in common bean Root length at soil depth of 60-75 cm 0.01 0.14*
(Sponchiado et al., 1989). BAT 477 showed this ability under
field conditions. Activation of this mechanism is linked with
root traits that contribute to improved acquisition of water Figure 1. Methodology to evaluate phenotypic differences in BT 74-1-1
and nutrients and result in greater seed yield under stress
Rainfed grain yield (kg ha-1)
root development and distribution under drought stress using 1300 BT 60-1-1
conditions. But combination of deep rooting ability with transparent plastic tubes filled with soil. The methodology BT 41-1-1 BT 56-1-1
improved partitioning of photosynthates to grain can not only involves filling of tubes with soil, inserted into PVC tubes, 1200 BT 53-1-1 BT 4-1-1 BT 17-1-1 BT 88-1-1
improve yield potential but also contribute to superior mounted to wooden racks, cut into different soil depths, soil + BT 99-1-1 BT 91-1-1
BT 41-1-1 BT 79-1-1 BT 72-1-1 BT 29-1-1SEA 5
adaptation to drought stress. We developed a greenhouse roots collected, roots washed and cleaned, scanned for root 1100 BT 95-1-1 BT 26-1-1 BT 83-1-1
soil tube method to quantify phenotypic differences in root images, and analyzed for root attributes. BT 59-1-1
BT 85-1-1 BT 12-1-168-1-1
1000 BT 9-1-1 BT 94-1-1 BAT 477
development and distribution under simulated soil drying BT 35-1-1
BT 1-1-1 Mean: 994
(terminal drought). This system is used to quantify phenotypic 900 BT 13-1-1
BT 15-1-1 BT 21-1-1
BT 80-1-1 BT 115-1-1
differences among 97 RILs of DOR 364 x BAT 477 in root BT 51-1-1 BT 30-1-1
DOR 364 25-1-1BT 69-1-1 BT 34-1-1
development under drought stress and correlation with field 800 BT
BT 2-1-1 BT 33-1-1
BT 50-1-1BT 65-1-1 BT 45-1-1
performance. The phenotypic data generated from this study BT 104-3
700 BT 31-1-1
will be used for eventual gene tagging for drought resistance. Mean: 59
40 45 50 55 60 65 70 75 80
Deep rooting at 35 days after planting
Materials and Methods drought - soil tubes (cm)
Figure 4. Identification of genotypes that combine superior seed
A greenhouse study was conducted at CIAT - Palmira using a yield with superior deep rooting under stress conditions.
mix of an Andisol (from Darien of Colombia) with river sand Genotypes with greater deep rooting and seed yield were
(2:1 w/w). Plants were grown for 48 days in plastic cylinders identified in the upper, right hand quadrant.
(80 cm long with 7.5 cm diameter) inserted in PVC tubes
(Figure 1). The trial included 97 RILs of the cross DOR 364 x
BAT 477 along with two parents and one check SEA 5 to
determinate genotypic differences in root development and • Greenhouse evaluation of 100 bean genotypes using soil
Figure 2. Influence of terminal drought stress on total root tube method for root phenotyping resulted in identification
distribution under drought stress. The trial was planted as a length of 11 genotypes of the cross DOR 364 X BAT 477
randomized complete block arrangement with two levels of of four genotypes BT 34-1-1, BT 79-1-1, BT 77-1-1 and
under greenhouse conditions, Palmira, 2007. Transgressive BT 55-1-1 that were superior in their total root
water supply: 80% field capacity (well-watered) and segregation was observed in rooting ability.
withholding of watering (to simulate terminal drought stress development under terminal drought stress conditions.
conditions) as main plots and genotypes as sub-plots with • The genotypes SEA 5, BT 83-1-1, BT 91-1-1, BT 29-1-1
Significant genotypic differences were observed in terms of and BT 61-1-1 were superior in their development of deep
three replications. Soil was fertilized with adequate level of deep rooting. Under terminal drought the genotypes SEA 5,
nutrients. Treatments of water stress were imposed after 10 roots.
BT 83-1-1, BT 91-1-1, BT 29-1-1 and BT 61-1-1 were • The superior performers under drought stress developed a
days of initial growth of plants. Plants with well-watered deeper rooted than parents at 35 days after planting (Figure
treatment were maintained by adding small amounts of more vigorous root system and deeper roots.
3). The genotypes BT 23-1-4, BT 51-1-1, BT 9-1-1 and BT • It appears that greater rooting depth and access to
water every two days and plants with terminal drought were 50-1-1 showed shallow rooting than parents under terminal
monitored for water stress. Plants were harvested at the age moisture alone will not assure good yield under drought.
drought stress. Further work is needed under field conditions to verify this
of 48 days after establishment, i.e., 38 days after
withholding of water application. 80 observation.
At the time of harvest leaf area; shoot biomass distribution,
with drought stress (cm)
and root traits were determined. The soil from the tube was LSD0.05: 16
Deep rooting at 35 dap
removed and sliced into 6 layers (0-5, 5-10, 10-20, 20-40,
40-60 and 60-75 cm). Roots in each soil layer were washed
and root length, mean root diameter, specific root length, and Beebe, S., I. M. Rao, C. Cajiao and M. Grajales. 2008.
root dry weight (g) were determined. Root length and mean Selection for drought resistance in common bean also
root diameter were measured with an image analysis system 50 improves yield in phosphorus limited and favorable
(WinRHIZO, Regent Instruments INC, v.2003 b). Root traits environments. Crop Science 48: 582-592.
were correlated with grain yield from field studies conducted Rao, I. M. 2002. Role of physiology in improving crop
at CIAT-Palmira over three seasons (2005, 2006 and 2007). adaptation to abiotic stresses in the tropics: The case of
common bean and tropical forages. In: M. Pessarakli (ed).
30 Handbook of Plant and Crop Physiology. Marcel Dekker, Inc.,
New York, USA pp. 583-613.
T 1 -4
B -1 -
Sponchiado B., J. White, J. Castillo and P. Jones. 1989.
Root growth of four common bean cultivars in relation to
Genotype drought tolerance in environments with contrasting soil types.
Soil moisture and temperature: During the greenhouse Figure 3. Deep rooting at 35 days after planting (dap) of 11 Expl Agric.25: 249-257
study, the average of maximum and minimum air genotypes of the cross DOR 364 X BAT 477 under terminal White, J. W., and S. P. Singh. 1991. Breeding for
temperatures were 39.7oC and 20.5oC; with a maximum adaptation to drought. p. 501-506. In A. van Schoonhoven
photon flux density of 1100 µmol m-2 s-1. Soil bulk density drought stress in greenhouse conditions, Palmira, 2007
was 1.2 g cm-3. The final soil moisture for the plants under and O. Voyset (ed.) Common beans: Research fro crop
terminal drought was 28% of field capacity. Correlation coefficients between grain yield in the field over improvement. CAB International. Wallingford, UK & CIAT,
3 seasons and root traits from the greenhouse study indicated Cali, Colombia.
Rooting ability: Results on total root length showed
significant genotypic variation under terminal drought (Figure
2). The genotypes BT 34-1-1, BT 79-1-1, BT 77-1-1 and BT
that greater grain yield under rainfed conditions was
positively related to total root length, mean root diameter, Acknowledgements
root volume, deep rooting at 35 days after planting and root This work is partially supported from the funds of BMZ-GTZ
55-1-1 were superior in total root length under terminal
drought than parents and check, while the genotypes BT 19- length at soil depth of 60-75 cm (Table 1). This observation
(Project No. 05.7860.9 – 001.00; Contract No. 81084613) and
1-1, BT 69-1-1, BT 6-1-1 and BT 74-1-1 were lower than indicates that several superior performers under drought
developed deeper roots (Figure 4) and greater amount of fine Tropical Legumes I project of the Generation Challenge Program
parents in root development under terminal water stress
conditions. roots of CGIAR.