JARQ 42 (3), 157 – 162 (2008) http://www.jircas.affrc.go.jp

Growth Responses of Seedlings in Oryza glaberrima
Steud. to Short-term Submergence in Guinea, West
AfricaYukiko JOHO1,3, Kenji OMASA1, Naoyoshi KAWANO2,3 andJun-Ichi SAKAGAMI*2,3
Graduate School of Agricultural and Life Sciences, The University of Tokyo(Bunkyo-ku, Tokyo 113–8657, Japan)
2
Division of Crop Production and Environment, Japan International Research Center for Agricultural
Sciences (Tsukuba, Ibaraki 305–8686, Japan)
3
Section de programme du riz, Institut de Recherche Agronomique de Guinée (IRAG)(BP 1523, Conakry, Guinea)
1

Abstract

In inundation areas in rainfed lowland and inland valleys of Guinea as well as other regions in Africa,
submergence for a few days to a few weeks with a water depth less than 50 cm occurs in rice cultivation
during the rainy season. Young rice seedlings after transplanting are particularly vulnerable to submergence stress. Oryza glaberrima Steud. is well adapted to growth in inundation areas with deepwaterconditions in West Africa; however, it is not evident whether it resists short-term submergence stressafter transplanting. The purpose of the study was to understand the physiological responses of rice
plants after transplanting to short-term submergence stress under rainfed conditions for O. glaberrima
by comparison with several genotypes of Oryza sativa L. from Guinea. Eight genotypes of O. glaber­rima and seven genotypes of O. sativa including two shoot elongation genotypes, one submergence tolerant genotype as a control cultivars, and four genotypes of common cultivars in West Africa were used.
Thirty day-old seedlings were submerged completely for 10 days with medium deepwater conditions at
45 cm water depth at 13 days after transplanting in a lowland field. O. glaberrima showed higher shootelongation ability during submergence than any genotype of O. sativa that we tested. However, O. gla­
berrima lodged easily after desubmergence due to longer and rapid shoot elongation during submergence, and thus triggered a decrease in its survival rate. The submergence tolerant genotype of O.
sativa maintained the dry matter weight of the leaf blade during submergence through the inhibition ofshoot elongation. We suggest that O. glaberrima is susceptible to short-term submergence while it may
adapt to prolonged flooding because of improved restoration of aerial photosynthesis and survival rate
through shoot elongation ability.
Discipline: Crop production
Additional key words: anaerobic conditions, dry matter, leaf expansion, shoot elongation, survival

Introduction
Shallow, submergence-prone lands are generally
favorable for rice production except that they are subject
to unpredictable, short-term submergence that may damage the crop, especially when flooding occurs soon after
transplanting10. Moreover, excess water triggers serious
damage to the growth and survival rate of rice11,12. Floodconditions differ in duration and water depth. Therefore,

different morphological or physiological traits are required
to adapt to each environment3. Setter et al.15 describedthat elongation ability is required in areas where the water
depth generally exceeds 50 cm for more than 14 days inorder to resume aerobic metabolism. On the other hand,
many non-elongation-of-shoot cultivars during submergence show tolerance to short-term submergence for a
few days or weeks17. One of the adverse factors of shootelongation is an increase in carbohydrate consumption forcell division, cell elongation and maintenance of the elon-

This paper reports the results obtained in the joint project on “Improvement of water stress resistance in rainfed rice in Africa” with
Institut de Recherche Agronomique de Guinée in Republic of Guinea from May 2004 to March 2007.
*Corresponding author: e-mail sakajun@affrc.go.jp
Received 19 November 2007; accepted 28 December 2007.

157

Y. Joho et al.

gated shoot5,17,19. Therefore, reduced carbohydrate metabolism during submergence is important for short-term
submergence tolerance7. Tolerance is a physiological
adaptation, whereby the plant can change metabolic pathways to adapt to the submergence environment; meanwhile, avoidance is a morphological adaptation, whereby
the plants can avoid stress conditions to keep metabolic
pathways in normal conditions2.
In West Africa, about 40% of the cultivated area israinfed lowland. In coastal areas, the inundation areas inlowland and inland valleys of Guinea, submergence often
lasts for a few days to a few weeks with a water depth ofless than 50 cm during the rainy season. Young rice seedlings after transplanting are particularly vulnerable to submergence stress. Oryza glaberrima Steud. adapts well ininundation areas with deepwater conditions in West
Africa4. Deepwater rice is usually flooded deeper than 50
cm for one month or longer during the growing season.
Futakuchi et al.2 demonstrated that the chlorophyll content
of the leaf blade and photosynthetic O2 evolution rate of O.
glaberrima were maintained more strongly than those of
O. sativa L. under deepwater conditions. O. glaberrima
also showed higher shoot elongation than O. sativa. In thelight of this evidence, it is reasonable to suppose that O.
glaberrima has higher resistance to deepwater stress.
Although limited research has been carried out into thephysio-morphological responses to deepwater of O. gla­
berrima, little is known about their submergence tolerance
to short-term submergence stress after transplanting. The
purpose of this study is to investigate how O. glaberrima
responds to short-term submergence stress compared to O.
sativa after transplanting in rainfed lowland in Guinea.

Materials and methods
Eight genotypes of O. glaberrima and seven genotypes of O. sativa were examined (Table 1). In O. glaber­rima (DRL), five genotypes were from Mali, two from
Guinea and one genotype from Senegal, and these genotypes are adapted to deepwater to rainfed lowland. In O.
sativa, one submergence tolerant genotype (ST) and two
shoot elongation genotypes (SE) were donated from theInternational Rice Research Institute, two genotypes
adapted to deepwater (DW) were from Mali and two genotypes adapted to rainfed lowland (RL) from Guinea13.
Submergence tolerance is the ability of rice plants to survive 10–14 days of complete submergence and renew its
growth when the water subsides with no stem elongation
during submergence3,5,15. The shoot elongation typeincreases plant length by the elongation of internodes, leaf
sheaths, leaf blades, or a combination of these.
Rice seedlings were transplanted in the experimental
lowland field of Foulaya Agricultural Research Center inthe Republic of Guinea (10º 0′ N, 12º 9′ W) at 17 days after
seeding with 121 hills (11 × 11) for the individual genotypes at a density of 16.7 hills m-2 (30 cm × 20 cm) andtwo replicates. The paddy soil was Ferralsols, and characterized as a sandy soil. The pH of the soil was 4.2 before
transplanting. Rice plants were flooded completely at 13days after transplanting for 10 days at a 45 cm water
depth. The flooded water was very muddy during the submergence. The water level was kept at 2 cm depth before
and after flood treatment. Floodwater in the experimentfield was drained continuously during the flooding. The
water temperature was measured at four corners at a 30

Table 1. List of genotypes examined in the experiment
SpeciesAbbreviation name

Genotypic group

Genotype

Origina)O. glaberrima

DRL
DRL
DRL
DRL
DRL
DRL
DRL
DRL

Deepwater to rainfed lowland
Deepwater to rainfed lowland
Deepwater to rainfed lowland
Deepwater to rainfed lowland
Deepwater to rainfed lowland
Deepwater to rainfed lowland
Deepwater to rainfed lowland
Deepwater to rainfed lowland

Alyba
Bagua Kandie
CG14
Gbagaye
Salifore
Saligbeli
Simo Bareo
Simo Boro

Mali
Mali
SenegalMali
GuineaGuineaMali
Mali

O. sativa

DW
RL
RL
DW
SE
SE
ST

Deepwater
Rainfed lowland
Rainfed lowland
Deepwater
Shoot elongation
Shoot elongation
Submergence tolerance

Bouba Moussa
CK21
CK40
Gorbal
IR62293-2B-18-2-2-1-3-2-3
IR72431-5B-18-B-10-1
IR67520-B-14-1-3-2-2

MaliGuineaGuinea
Mali
IRRI
IRRI
IRRI

a): Origins include an organization.
158

JARQ 42 (3) 2008

Growth Responses of Oryza glaberrima Steud.

Results
1. Shoot elongation
Figure 1 shows the changes of plant length during
the experiment from 14 DBS to 46 DAS (36 days after
water receded) for each genotypic group. The submergence treatment was performed for 10 days. The average
plant length before submergence was 24.9 cm to 32.1 cm
in all the genotypic groups. In all the groups except for
ST, the top leaf reached to the water surface during submergence. The plant length of DRL was the lowest at 1
DBS among all the genotypic groups, while it was thehighest at 11 DAS. DRL increased in length rapidly dur-Dry matter weight (g plant–1)

0.12

DRL

0.12

RL

0.12

ing submergence compared to the other genotypic groups
in O. sativa. A significant difference in plant length wasrecognized between DRL and the other genotypic groups
at 11 DAS at p < 0.01. The averages for shoot length
elongation during submergence of DRL, RL, DW, SE, andST were 37.5, 17.4, 17.0, 15.6, and 6.8 cm, respectively.
All the genotypic groups except for ST decreased plant
length because of the death of elongated leaves after thewater level receded to 29 DAS.
2. Leaf area and dry matter production
Dry matter weights of leaf blades and stems at 14
DBS, 1 DBS and 11 DAS of the genotypic groups areshown in Fig. 2. All the genotypes increased in total dry
80
70

Plant length (cm)cm depth in the morning (9:00), noon (12:00) and evening(16:30). The averages of water temperature during the
day for 10 days submergence were from 25.6ºC to
33.1ºC.
The timing of each measurement was described as
the number of days from the day of beginning the submerged treatment. The plant length of five plants wasmeasured in the field using a 50 cm ruler at one day before
submergence (DBS), and 11, 29 and 46 days after submergence (DAS). The leaf area of five plants was measured
using an automatic area meter (AAM-9, Hayashi Denko
Co. Ltd.) at 14 DBS, 1 DBS and 11 DAS. The leaves (leafblade) and stems (culm + leaf sheath) of five plants were
harvested and dried in an oven for 48 hours at 80ºC tomeasure the dry matter weight at 14 DBS, 1 DBS and 11
DAS. The degree of lodging at 5 days after the waterlevel receded (15 DAS) was scored from 1 (no-lodging) to
5 (complete lodging). The survival rate was calculated
through the evaluation of plants growing with green leaves
at 19 days after the water level receded (29 DAS).

**

60
50
40
30
20
10
0
-14

-1

11

29

Day aft er flood t reat ment
Fig. 1. Change in plant length during the experiment●:DRL; Deepwater and rainfed lowland rice in O.
glaberrima, □:RL; Rainfed lowland rice in O. sativa,▲:DW; Deepwater rice in O. sativa, :SE; Shootelongation rice in O. sativa, :ST; Submergence tolerance rice in O. sativa. The vertical bars indicate
standard deviation of the means of ten plants.

DW

0.12

SE

0.12

0.1

0.1

0.1

0.1

0.1

0.08

0.08

0.08

0.08

0.08

0.06

0.06

0.06

0.06

0.06

0.04

0.04

0.04

0.04

0.04

0.02

0.02

0.02

0.02

0.02

0

0

0
-14 -111-14 -1 1146

0-14 -1 11ST

0-14 -1 11-14 -1 11

Day after flood treatment
Fig. 2. Change in dry matter weight of leaf blade and stem before and after desubmergence
Vertical error bars indicate a standard deviation among genotypes except for ST.
: Leaf blade,: Stem.
159

6

20

5
Lodging score

25

15
10
5
0

RL

DW

SE

ST

Fig. 3. Change in leaf area before and after desubmergence
Vertical error bars indicate a standard deviation
among genotypes except for ST.
: 14 DBS,: 1 DBS,: 11 DAS.

matter weight of shoots between 1 DBS and 11 DAS
except for RL. The total dry matter weight at 11 DAS was
the largest in ST, and the smallest in RL. The partitioningof the dry matter weight of stem to total dry matter weight
during submergence was changed due to the genotypicgroup. The partitioning of the dry matter weight of stem
to total dry matter weight before and after submergence
was 46.3% and 68.8% in DRL, 49.4% and 78.8% in RL,
54.0% and 79.4% in DW, 50.9% and 70.8% in SE, and43.6% and 56.6% in ST.
The leaf area decreased at 11 DAS compared to 1
DBS in all the genotypic groups (Fig. 3). In particular, in
RL (‑63.1%) and DW (‑58.6%) the leaf area decreasedmuch more during submergence by the calculation of thedecrease ratio [(1 DBS-11 DAS)/1 DBS] in the leaf area,
compared to DRL (‑36.2%), SE (‑35.2%) and ST(‑28.3%). Leaf area at 1 DBS and 11 DAS was the largest
in ST. There was a significant positive correlation (r =0.97, P < 0.01) between dry matter weight of the leaf blade
and leaf area at 14 DBS, 1 DBS and 11 DAS.
3. Lodging and plant survival
There was a high positive correlation (P < 0.01, r =0.86) between shoot length elongation during submergence and lodging score at 15 DAS (Fig. 4). DRL showed
higher shoot elongation during submergence and a higher
lodging score after desubmergence than other genotypicgroups. On the other hand, ST showed the opposite features to DRL with lower shoot elongation and lodging
score. RL, DW and SE showed intermediate traits inshoot length elongation and lodging score between DRL
and ST. Figure 5 shows the relationship between shootlength elongation during submergence and survival rate at
29 DAS. There was a negative correlation between shootlength elongation and survival rate (P < 0.05, r = -0.66).
ST showed the highest survival rate (93%) and the shortest shoot length elongation (6.8 cm) as well as IR 62293160

r = 0.86**

4
3
2
1

DRL

0
0

10

20

30

40

50

Shoot length elongation (cm)Fig. 4. Relationship between shoot length elongation
during submergence and lodging after
desubmergence● :DRL; Deepwater and rainfed lowland rice in O.
glaberrima, □ :RL; Rainfed lowland rice in O. sativa,▲:DW; Deepwater rice in O. sativa, :SE; Shootelongation rice in O. sativa, :ST; Submergence tolerance rice in O. sativa.

Survival rate (%)

Leaf area (cm2 plant–1)

Y. Joho et al.

100
90
80
70
60
50
40
30
20
10
0

r = –0.66**

0

10

20

30

40

50

Shoot length elongation (cm)Fig. 5. Relationship between shoot length elongation
during submergence and survival rate after
desubmergence
Survival rate is calculated for number of plants
before submergence divided by number of surviving
plants at 19 day after desubmegence.
● :DRL; Deepwater and rainfed lowland rice in O.
glaberrima, □ :RL; Rainfed lowland rice in O. sativa,▲:DW; Deepwater rice in O. sativa, :SE; Shootelongation rice in O. sativa, :ST; Submergence tolerance rice in O. sativa.

2B-18-2-2-1-3-2-3 (86%, 11.5 cm) in the SE genotype
group. The survival rate of DRL was lower comparedwith ST.

Discussion
All the genotypes showed shoot length elongation
during submergence for 10 days with a 45 cm water depth
JARQ 42 (3) 2008

Growth Responses of Oryza glaberrima Steud.

in the paddy field, and DRL had the highest shoot elongation ability (Fig. 1). The average shoot length elongationof DRL during submergence was 2.2-, 2.2-, 2.4- and 5.5fold greater than that of RL, DW, SE and ST, respectively,
in O. sativa. The results concur with those of Futakuchi
et al.2 who pointed out that O. glaberrima shows higher
shoot elongation ability than O. sativa under flooding
conditions. The results suggest that DRL has different
traits to any of the genotypes of O. sativa that we tested
for shoot elongation responses to short-term submergencestress after transplanting in rainfed lowland in Guinea.
SE did not elongate its stem much during submergencesimilar to the RL and DW genotypes. It may be presumed
that the shoot elongation ability relates to the submergence period and growth stage of rice. A characteristic of
SE is internode elongation during submergence, but theinternode elongation does not start at an early growthstage after transplanting18, and was not observed in thisexperiment.
In the case of short-term submergence, the recoveryof plant growth after the water level recedes is also important5. All the genotypes except for ST showed the death ofelongated leaves. The leaves that elongated during submergence lodged after the water level receded, which
resulted in death. Another reason may be the failure ofphysiological adaptation to the environmental change
from anaerobic to aerobic conditions. In general, oxidative stress is a serious problem for survival in aerobic conditions; therefore, the plants have to contain mechanisms
for adequate protection from oxidative stress1. However,the plants damaged by flooding cannot rapidly initiate
their protection systems after the water level recedes8,9.
ST showed the highest survival rate, suggesting that ST
has a good ability to adjust to the environmental changes
in this experiment.
Mazaredo and Vergara11 showed that submergence
tolerant genotypes tended to have greater leaf areas withhigher carbohydrate and nitrogen contents during submergence compared to susceptible genotypes. In this experiment, ST had the highest leaf area and dry matter weightof the leaf blade and stem after desubmergence among the
genotypes analyzed (Fig. 3). Growth and photosynthetic
responses of lowland rice following complete submergence are related to the concentration of CO2 dissolved infloodwater14. Low CO2 concentrations do not only reduce
photosynthesis, but they also lead to adverse interactions
with high concentrations of ethylene6. We concluded that
it is not evident whether submergence tolerance depends
on the increase of shoot biomass during submergence.
Although shoot elongation during complete submergencecompetes with maintenance processes for energy and carbohydrates16, if the leaves can come into contact with the

air as a result of shoot elongation, rice plants may maintain their shoot growth such as dry matter weight and leaf
area. We focus attention on the partitioning of dry matterweight between the leaf blade and stem during submergence. The dry matter weight in the stem increased in all
the genotypes, while those in the leaf blade decreased
except for ST during submergence. Most of the genotypes concentrated the dry matter weight to the stem during submergence to support shoot elongation with a resulting decrease in leaf area. It was found through the field
experiment that ST maintains the dry matter weight ofleaf blades during submergence through the inhibition ofshoot elongation. Keeping dry matter weight in the leaf
blade during submergence may support recovery growth
after the water level recedes, by the maintenance of carbohydrate supply. However, maintaining the dry matterweight is difficult for long-term complete flooding,because of the limitation of photosynthetic activity underwater. From this viewpoint, shoot elongation ability toreturn to aerobic growth conditions is needed for longterm flood survival. DRL can grow by rapid shoot elongation during submergence after transplanting. However,
DRL lodges easily after desubmergence due to its elongated shoot resulting in a decreased survival rate (Fig. 5).
A further important point is that there is a close relationship between shoot length elongations less than 20 cm andthe survival rate. Most of the genotypes in DRL survived
as well as DW and RL while the elongation of DRL wasmostly larger than 28 cm. DRL exhibits rapid growth
characteristics of shoot elongation during submergence,
which is an important issue for growing DRL in regions
prone to submergence for prolonged periods, due to its
improved ability to restore aerial photosynthesis and produce an improved survival rate.

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JARQ 42 (3) 2008