AJCS 14(12):1935-1941 (2020)
doi: 10.21475/ajcs.20.14.12.2774

ISSN:1835-2707

Effect of soil moisture stress at booting and flowering stages on pollen development,pollination and fertilization in upland NERICA cultivars
Momoko IWATA-HIGUCHI1, *, Jun-Ichi SAKAGAMI2 and Sachio MARUYAMA3
1

Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan
Faculty of Agriculture, Kagoshima University, Kagoshima, Kagoshima 890-0065, Japan
3
Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan
2*Corresponding author: higuchi.momoko@gmail.com
Abstract
Spikelet sterility induced by soil moisture stress during reproductive development greatly limits grain yield in upland rice. This study
aimed to elucidate differences in responses to soil moisture stress for pollen development, pollination and fertilization among
upland rice cultivars. A greenhouse experiment with a split-plot design was performed for five different soil moisture treatments (T1
to T5) as the main plots and three cultivars (NERICA 1, NERICA 4 and Yumenohatamochi) as subplots, each with three replicates.
Plants in pots were grown under well-watered condition (T1) and various moisture stress conditions: moderate at the booting stage(T2), severe at the booting stage (T3), moderate at the flowering stage (T4) or severe at the flowering stage (T5). During the 9-day
stress period, soil moisture was maintained at -10 to -20 kPa for moderate moisture stress or -20 to -49 kPa for severe moisturestress under controlled irrigation. NERICA 1 had fewer differentiated microspores and developed pollen grains in T2 and T3 andshowed poorer anther dehiscence and fewer pollen grains on the stigma than did NERICA 4 and Yumenohatamochi. NERICA 4
showed a lower percentage of basal dehiscence in T4 and T5, causing fewer pollen grains to be deposited on the stigma than for
NERICA 1 and Yumenohatamochi. The results indicate that the highly sensitive process of fertilization are pollen development in
NERICA 1 and pollination in NERICA 4 under soil moisture stress.
Keywords: Anther dehiscence; drought; pollen grain; rice; spikelet sterility.
Abbreviations: DW_dry weight; FW_fresh weight; IKI_iodine potassium iodide; NERICA_New Rice for Africa; RWC_relative watercontent; SSA_Sub-Saharan Africa; SWC_soil water content; T1_well-watered; T2_moderate moisture stress at the booting stage;
T3_severe moisture stress at the booting stage; T4_moderate moisture stress at the flowering stage; T5_severe moisture stress at
the flowering stage; TW_turgid weight.
Introduction
In Sub-Saharan Africa (SSA), rice has risen in importance asconsumption has continuously increased (Gajigo and Denning,2010) and, thus, it is necessary to expand rice production. Riceis mainly grown in rainfed uplands or wetlands in SSA where
insufficient rainfall leads to soil moisture stress and limits riceproductivity. To improve production under these conditions,
new strains of rice have been developed. Since NERICAs,
inter-specific progenies of Oryza sativa L. and Oryza
glaberrima Steud., were developed in 1994 (Jones et al., 1997),
cultivation reached about 700,000 ha in SSA by 2009 (Diagne
et al., 2010). These strains are expected to be well adapted todrought-prone areas, showing relatively high yields even undersoil moisture stress (Somado et al., 2008). Nevertheless, amulti-location trial with 14 NERICA cultivars in Tanzania (Sekiya
et al., 2013) and a long-term experiment with cultivar NERICA
4 in Uganda (Tsuboi et al., 2018) revealed the close
relationship between yield and precipitation, indicating thatsoil moisture stress reduces grain yield in NERICAs. Thus,
recovery of yield reduction in NERICAs due to soil moisturestress is required to improve rice productivity in SSA.
Sekiya et al. (2013) and Tsuboi et al. (2018) demonstrated thatcompared to other growing periods, soil moisture stress during
periods of active meiosis and anthesis cause the largest
reduction in grain yield with low ripening ratio having thebiggest contribution to yield in NERICAs. Moreover, spikelet
sterility, which controls ripening ratio, was identified as thefactor significantly affecting grain yield in NERICA 4experiencing soil moisture stress from panicle initiation toanthesis (Alou et al., 2018). These observations suggest that, in
NERICAs, achieving spikelet fertilization is essential forreaching higher yield under soil moisture stress.
In rice, soil moisture stress during reproductive development,
particularly at meiosis and anthesis, causes severe spikelet
sterility (Matsushima, 1962; Saini and Westgate, 1999).
Generally, spikelet sterility induced by stress at meiosis mainly
leads to insufficient development of pollen grains in anthers(Sheoran and Saini, 1996; Nguyen and Sutton, 2009; Saragih etal., 2013), while stress at anthesis induces failure of pollination(Ekanayake et al., 1990; Liu et al., 2006; Rang et al., 2011) andpollen germination (Ekanayake et al., 1990; Liu et al., 2006; Fu
et al., 2011; Rang et al., 2011). Further, anther indehiscence
due to soil moisture stress at anthesis is considered to cause

1935poor pollination and consequently result in spikelet sterility(Ekanayake et al., 1990; Liu et al., 2006; Rang et al., 2011; He
and Serraj, 2012). Several reports have pointed out thatgenetic variation in pollen development (Fu et al., 2011) andpollination (Liu et al., 2006; Fu et al., 2011) are related todrought tolerance. However, the physiological andmorphological characteristics of reproductive processes undersoil moisture stress have not been extensively analyzed in
NERICAs.
In our previous study, differences in ripening ratio wereobserved among NERICAs under soil moisture stress at thebooting stage (Iwata-Higuchi et al., 2019), suggesting thepossibility of cultivar differences in spikelet sterility. Thus, wehere investigate the effect of soil moisture stress in NERICAs at
the booting or flowering stage on fertilization processes. In thepresent investigation, pollen development and pollination in
NERICA 1 and NERICA 4 were characterized and compared with
Yumenohatamochi, a Japanese drought-resistant uplandcultivar. Among NERICA cultivars, NERICA 1 (Atera et al., 2011;
Sekiya et al., 2013) and NERICA 4 (Kinyumu, 2009; Nassir et al.,2017) have been reported to show higher yields under drought
conditions in different countries and are widely grown as
adopted or certified cultivars in SSA (Diagne et al., 2010). We
discussed differences between fertilization responses in these
two leading NERICAs due to soil moisture stress.
Results
SWC and leaf RWC
Mean soil water content (SWC) and leaf relative water content(RWC) decreased during stress periods in all soil moisturestress treatments (T2 to T5) but no significant differences were
found among cultivars and in the interaction between
treatment and cultivar (Table 1). Moisture stress at theflowering stage (T4, T5) tended to cause lower SWC and leaf
RWC than at the booting stage (T2, T3).
Pollen development, pollination and spikelet fertility
The numbers of differentiated microspores and developed
pollen grains tended to be reduced in T2 and T3, except for
those of NERICA 4 which were hardly reduced (Fig. 1A). The
largest and significant reductions in the number ofdifferentiated microspores were observed in NERICA 1 underT3. In T3, NERICA 1 had significantly fewer differentiatedmicrospores than NERICA 4 and Yumenohatamochi. In contrast,
the number of differentiated microspores was less affected in
T4 and T5, and there were no significant differences amongcultivars.
With an increase in undeveloped pollen grains (Fig. 1A),
moisture stress tended to reduce the percentage of developed
pollen grains for all cultivars (Fig. 1B). Compared to T1, thepercentage of developed pollen grains of NERICA 1 andNERICA 4 was significantly lower in T3 and T5, respectively.
NERICA 1 had a significantly lower percentage of developed
pollen grains than NERICA 4 and Yumenohatamochi in T2 andT3, whereas there were no clear differences among cultivars
for T4 and T5.
The number of deposited pollen grains decreased greatly in T2
to T5 (Fig. 1C). In T1, Yumenohatamochi had significantly morepollen grains on the stigma than NERICA 1 and NERICA 4, and asimilar tendency (differences not significant) was observed forother stress treatments, except for T5. NERICA 1 showedslightly fewer deposited pollen grains than NERICA 4 formoisture stress at the booting stage (T2, T3), while NERICA 4
had fewer deposited pollen grains than NERICA 1 undermoisture stress at the flowering stage (T4, T5), although thedifferences were not significant.
All stress treatments considerably reduced spikelet fertility (Fig.
1D), and differences compared to T1 were significantly lower
for all cultivars in T3, T4 and T5, as well as NERICA 4 in T2.
Spikelet fertility tended to be lower in T4 and T5 than in T2 andT3. The largest reductions were observed for NERICA 4 under
T5, and NERICA 4 tended to have lower spikelet fertility than
NERICA 1 and Yumenohatamochi in T4 and T5. Spikelet fertilityof NERICA 1 was slightly lower than that of NERICA 4 andYumenohatamochi in T2 and T3. However, these cultivar
differences in spikelet fertility were not statistically significant.
Anther dehiscence
Stress treatments tended to reduce the percentage of basal
dehiscence for NERICA 1, and NERICA 4 showed a significantly
lower percentage of basal dehiscence in T4 and T5 than in T1(Fig. 2A). Although the differences were not significant, thepercentage of basal dehiscence in NERICA 4 was lower than in
the other cultivars in T4 and T5. NERICA 1 had a significantly
lower percentage of basal dehiscence than NERICA 4 andYumenohatamochi in T2. Compared to NERICA 1 and NERICA 4,
Yumenohatamochi tended to show a higher percentage ofbasal dehiscence both under well-watered condition (T1) andall stress treatments (T2 to T5). The length of antherdehiscence differed among cultivars and there was no clear
effect of treatment (Fig. 2B). NERICA 1 and NERICA 4 showed asignificantly smaller basal dehiscence than Yumenohatamochi
in T1, in which was also evident in T2 and to a lesser extent in
T3 to T5. In addition, the length of basal dehiscence of NERICA
4 tended to be shorter in T4 and T5 than that of the othercultivars.
The number of deposited pollen grains was positively
correlated with the percentage of basal dehiscence for all
cultivars (r = 0.455, p < 0.01, Fig. 3A), but there was no
significant relationship between the number of depositedpollen grains and the length of basal dehiscence (Fig. 3B).
Discussion
Meiosis and anthesis are regarded as two stages that arehighly sensitive to soil moisture stress in rice (Saini andWestgate, 1999). In the present experiment, soil moisturestress during meiosis (booting stage, T2, T3) and anthesis(flowering stage, T4, T5) reduced spikelet fertility (Fig. 1D) as
leaf RWC decreased (Table 1). The number of differentiatedmicrospores, the percentage of developed pollen grains, andthe number of deposited pollen grains were significantly
reduced by moisture stress at the booting and/or flowering
stages, and the effects of soil moisture stress on theseparameters differed among NERICA 1, NERICA 4 andYumenohatamochi (Fig. 1 A, B, C).
Moisture stress at the booting stage (T2, T3) reduced thenumber of differentiated microspores and lowered thepercentage of developed pollen grains in NERICA 1 more thanin NERICA 4 and Yumenohatamochi (Fig. 1A, B). Theseobservations suggest that water deficit inhibits pollen
differentiation and development in NERICA 1 more severely
than in the other cultivars. In addition, NERICA 1 had poorer
anther dehiscence (Fig. 2A) and tended to have relatively

1936

Table 1. Mean volumetric soil water content (SWC) and leaf relative water content (RWC) during moisture stress periods.
SWC
Leaf RWC
Treatment
Cultivar
(%)
(%)
T1
YHM
64.6
a
87.0
a
N1
61.6
a
89.7
a
N4
60.3
a
90.3
a
T2
YHM
12.4
b
82.2
ab
N1
12.8
b
82.3
ab
N4
12.6
b
77.0
ab
T3
YHM
12.0
b
72.1
ab
N1
12.4
b
75.6
ab
N4
12.1
b
76.3
ab
T4
YHM
9.8
b
70.2
ab
N1
11.1
b
76.3
ab
N4
11.9
b
76.0
ab
T5
YHM
9.1
b
62.5
b
N1
10.9
b
68.8
ab
N4
9.6
b
63.9
b
T1
62.2
A
89.0
A
T2
12.6
B
80.5
AB
T3
12.2
B
74.7
B
T4
10.9
B
74.2
BC
T5
9.9
B
65.1
C
Treatment (T)****Cultivar (C)
n.s.
n.s.
TxC
n.s.
n.s.
YHM: Yumenohatamochi, N1: NERICA 1 and N4: NERICA 4. SWC and leaf RWC of the control are means during the moisture stress periods of booting and flowering stages. ** and n.s. denotesignificant difference at p < 0.01 and not significant, respectively. Values followed by the same letter within each column do not differ at p < 0.05 by Tukey’s test.

Fig 1. Effect of soil moisture stress on the number of differentiated microspores (A), percentage of developed pollen grains (B), number of deposited pollen
grains (C) and spikelet fertility (D). Abbreviations are the same as for Table 1. * and ** denote significant differences from values in T1 of the same cultivar at p
< 0.05 and p < 0.01, respectively, by Dunnett’s test. Bars with the same letter within each treatment do not differ at p < 0.05 by LSD test.

1937

Fig 2. Effect of soil moisture stress on the percentage (A) and length (B) of basal dehiscence. Abbreviations are the same as for Table 1. ** denotes significant
difference from values in T1 of the same cultivar at p < 0.01 by Dunnett’s test. Bars with the same letter within each treatment do not differ at p < 0.05 by LSD
test.

Fig 3. Relationships between the percentage (A) or length (B) of basal dehiscence and the number of deposited pollen grains on stigma. Abbreviations are thesame as for Table 1. ** and n.s. denote significant difference at p < 0.01 and not significant, respectively.

Fig 4. Daily mean, maximum and minimum temperature in the greenhouse during growing period. Bars with YHM, N1 and N4 indicate the range in heading
date of Yumenohatamochi, NERICA 1 and NERICA 4, respectively.

1938

fewer deposited pollen grains on the stigma at the booting
stage (Fig. 1C) than NERICA 4 and Yumenohatamochi. Soil
moisture stress inhibits pollen development, decreases thesize of pollen grains (Liu et al., 2006) and reduces antherdehiscence (Matsui et al., 1999). The positive correlation
between the percentage of basal dehiscence and the numberof deposited pollen grains (Fig. 3A) suggests that insufficientpollen development causes poorer pollination in NERICA 1
than the other cultivars.
Starch accumulation in pollen grains plays an important role inpollen differentiation and development under soil moisturestress (Sheoran and Saini, 1996; Fu et al., 2011). A previous
report (Sheoran and Saini, 1996) suggests that enzyme
activities involved in sucrose cleavage and starch synthesis are
depressed in pollen grains under soil moisture stress, whileother investigations (Selote and Khanna-Chopra, 2004; Nguyen
et al., 2010; Fu et al., 2011) indicate that insufficient defense
against oxidative stress inhibits pollen development under soil
moisture stress. Further investigation is therefore needed toanalyze physiological mechanisms that cause differences inpollen differentiation and development between NERICA 1 andNERICA 4 under soil moisture stress.
Moisture stress at the flowering stage (T4, T5) hardly affected
the number of differentiated microspores and the percentage
of developed pollen grains (Fig. 1 A, B). The significant decline
in the percentage of developed pollen grains for NERICA 4 in
T5 is likely attributable to the stress treatment starting 2-6
days before heading, which partly suppresses pollen
maturation. In contrast, moisture stress at the flowering stage
markedly reduces the number of pollen grains deposited on
the stigma (Fig. 1C), and the number of deposited pollen grains
was smaller in NERICA 4 than in NERICA 1 andYumenohatamochi. The percentage and the length of basal
dehiscence of NERICA 4 tended to be inferior to those of
NERICA 1 and Yumenohatamochi at the flowering stage (Fig.
2A, B), and the percentage of basal dehiscence wassignificantly related to the number of deposited pollen grains(Fig. 3A). These results suggest that the inferior antherdehiscence in NERICA 4 reduced the number of pollen grainsdeposited on the stigma as compared to the other cultivars.
The present investigation failed to detect a significant
correlation between the length of basal dehiscence and thenumber of deposited pollen grains on the stigma (Fig. 3B),
which is inconsistent with the results of Matsui and Kagata(2003). This discrepancy is probably due to a portion of thepollen grains sticking to the inside the anthers despite thepores being sufficiently opened under conditions of drought(Liu et al., 2006).
NERICA 1 and NERICA 4 had lower percentages of basal
dehiscence and smaller basal pores than Yumenohatamochi
both under well-watered (T1) and stressed conditions (T2 toT5) (Fig. 2A, B). Similarly, NERICA 1 and NERICA 4 had fewer
deposited pollen grains on the stigma than Yumenohatamochi
under well-watered and stressed conditions (Fig. 1C). These
results indicate that poorer basal dehiscence in NERICA 1 andNERICA 4 causes deposition of fewer pollen grains on the
stigma irrespective of soil moisture stress. In the present
experiment, plants may have been transiently exposed to hightemperatures at anthesis (Fig. 4), and cultivar differences inanther dehiscence may have been affected by differences intolerance to high temperature. However, as the length of basal
dehiscence under high temperature strongly corresponds tothat under normal conditions (Matsui et al., 2005), basal
dehiscence ability in NERICAs might be genetically inferior tothat in a Japanese upland cultivar, irrespective of growing
conditions.
In the present investigation, NERICA 1 and NERICA 4 tended tohave lower spikelet fertility than the other cultivars undermoisture stress at booting (T2, T3) and flowering (T4, T5)
stages, respectively (Fig. 1D); however, these cultivar
differences were not significantly demonstrated by this dataset.
Although there were significant differences in differentiationand development of pollen grains and pollination amongcultivars (Fig. 1A, B, C), spikelet fertility did not necessarilyreflect these significant differences. Spikelet fertility isexpressed as the product of fertilization components involvedin the four main phases of fertilization (Satake and Shibata,1992): microspore differentiation, microspore development,pollen shedding on the stigma, and pollen germination andfertilization. The last phase, which was not evaluated in thepresent experiment, may affect spikelet fertility, andinvestigations of pollen germination and fertilization are thus
required to analyze differences in spikelet fertility under soil
moisture stress.
Materials and Methods
Plants and growth conditions
Experiments were conducted in a greenhouse at theAgricultural and Forestry Research Center, University ofTsukuba, Tsukuba, Ibaraki, Japan in 2013. NERICA 1, NERICA 4
and Yumenohatamochi were used. Twenty pre-germinatedseeds were sown in a circular pattern in each 1/5000 a Wagner
pot filled with 3 kg of nursery soil containing 1.0 g N, 1.8 g P2O5
and 1.0 g K2O on April 30. Each pot was top-dressed with 1.0 g
N at 56 days after seeding. Tillers were removed as they
emerged in order to obtain uniform main culms.
Air temperature in the greenhouse was measured andrecorded every 20 min using a thermologger (TR-72U, T&D
Corporation, Nagano, Japan). The daily mean, maximum andminimum temperatures throughout the growing period areshown in Fig. 4. During the heading period of the threecultivars, daily mean and maximum temperatures were 31.2
and 42.2C, respectively.
Experimental design and treatment
In the experiment, five moisture treatments (T1-T5) were
tested in three cultivars (NERICA 1, NERICA 4 andYumenohatamochi) with three replicates each. A split-plot
design was used with the treatments as the main plots andcultivars as subplots.
In T1, the soil was well-watered and maintained above field
capacity at -3 kPa throughout the growing period. In the otherfour treatments, soil moisture stress was induced for 9 days at
two different stages: booting stage stress started 9-12 days
before heading (81-88 days after seeding) in T2 and T3 andflowering stage stress started 2-6 days before heading (94-100
days after seeding) in T4 and T5. The heading date for each
cultivar was anticipated by observing the leaf number index
and measuring the distance between auricles of the flag andpenultimate leaves. Aside from periods of stress treatment,
soil moisture in pots was maintained above field capacity.
Soil moisture stress management
Irrigation was performed three times daily (8:00, 11:00 and1939

14:00). To produce the stress periods for T2 to T5, water was
withheld from the pots on the day before the start of the soil
moisture stress treatment. To maintain the soil water potentialfrom -10 to -20 kPa for moderate soil moisture stress (T2, T4)
and from -20 to -49 kPa for severe soil moisture stress (T3, T5),
the pots were watered until the water potential reached theupper bound of the specified range only when the water
potential decreased below the lower bound.
Soil water potential was estimated by measuring volumetric
SWC with a Hydrosense Soil Water Sensor (CD620, Campbell
Scientific, UT, USA) at a depth of 0-10 cm based on a water
retention curve. SWC was plotted against soil water potential
measured with a soil water meter (PF-33, Fujiwara Scientific,
Tokyo, Japan) on soil prior to seeding.

spikelets were separated in 80% ethanol solution (specificgravity, 0.86), sinking spikelets were counted as fertilized
spikelets, and the spikelet fertility (%) was calculated.
Statistical analysis
Statistical analysis was performed using Statistix 9 software,version 9.0 (Analytical Software 2008, Tallahassee, FL, USA).
Analysis of variance was conducted, and Tukey’s test or the
LSD test was carried out to check for significant differences at
p < 0.05 in parameters among treatments and cultivars. To
identify significant differences between the control and eachtreatment for the same cultivar, Dunnett’s pairwise multiple
comparison was used. Percentage data were analyzed afterarcsine transformation.

Measurements
Conclusion
To determine leaf RWC, the topmost fully expanded leaf blade
was excised on 3, 6 and 9 days after starting the treatment.
Fresh weight (FW) was quickly determined, and the leaf wassoaked in distilled water for 12 h at 4C and weighed todetermine turgid weight (TW). Leaves were oven-dried for 48 h
at 80C before obtaining dry weight (DW). Leaf RWC wasestimated according to Barrs and Weatherley (1962) as
follows:
Leaf RWC (%) = [(FW - DW) / (TW - DW)] × 100
Spikelets from the uppermost four primary rachis branches on
three panicles per pot were collected to investigate pollen
grains just before anthesis. Five spikelets not including any that
had already reached anthesis were sampled when the first
spikelet with anthesis was observed. The spikelets were then
immediately preserved with FAA fixative (50% ethanol, 5%acetic acid, 10% formaldehyde and 35% distilled water). The
numbers of developed and undeveloped pollen grains peranther were determined with 30 anthers per pot by themethod of Kariya et al. (1985). Anthers were removed fromeach fixed spikelet, crushed with a needle and then suspended
in a 2 mL solution consisting of 50% ethanol, 2% glycerin, 40%
iodine potassium iodide (IKI) and 8% distilled water. Drops ofthe pollen suspension were placed on a hemocytometer slide
2
and IKI-stained and -unstained pollen grains in each 1 mm cellwere counted as developed and undeveloped grains,respectively, under an optical microscope (DM500, Leica
Microsystems, Tokyo, Japan). Measurements were conductedfour times per pot. The number of differentiated microspores
per anther was determined as the sum of developed andundeveloped pollen grains. Additionally, the percentage ofdeveloped pollen grains was expressed as the percentage ofthe number of developed pollen grains to the number ofdifferentiated microspores.
To examine pollination, just after anthesis (within spikelet
opening), 15-20 spikelets from the uppermost four primaryrachis branches per pot were sampled and fixed as describedabove. Three stigmas per pot were dissected from randomly
selected spikelets and stained with cotton blue solution. The
number of pollen grains deposited on each stigma wascounted under an optical microscope. In addition, thepercentage and length of anther dehiscence at the basal poreon the thecae, which contributes to reliable pollination(Matsui and Kagata, 2003), were estimated with ten anthersfrom different spikelets per pot under a stereo microscope(SZH, Olympus Corporation, Tokyo, Japan) using a micrometer.
At maturity, three panicles per pot were harvested andhand-threshed. Following the method by Kobata et al. (2010),

The responses of pollen development and pollination to soil
moisture stress at the booting and flowering stages differedamong cultivars, and even within NERICAs. Soil moisture stressat the booting stage inhibited pollen differentiation anddevelopment more severely, causing poorer basal dehiscenceand fewer pollen grains on the stigma in NERICA 1 than in
NERICA 4 and Yumenohatamochi. In addition, a greater decline
in basal dehiscence in NERICA 4 resulted in fewer depositedpollen grains on the stigma than in NERICA 1 andYumenohatamochi under soil moisture stress at the flowering
stage. These findings suggest that the sensitivity of thefertilization process to soil moisture stress differs among
NERICAs. The underlying mechanisms of the different
responses to soil moisture stress need to be elucidated inorder to improve productivity of NERICAs under conditions ofsoil moisture stress.
References
Alou IN, Steyn JM, Annandale JG, van der Laan M (2018)
Growth, phenological, and yield response of upland rice®
(Oryza sativa L. cv. Nerica 4 ) to water stress during different
growth stages. Agr Water Manage. 198:39-52.
Atera EA, Onyango JC, Azuma T, Asanuma S, Itoh K (2011) Field
evaluation of selected NERICA rice cultivars in Western Kenya.
Afr J Agric Res. 6:60-66.
Barrs HD, Weatherley PE (1962) A re-examination of therelative turgidity technique for estimating water deficits inleaves. Aust J Biol Sci. 15:413-428.
Diagne A, Midingoyi SKG, Wopereis M, Akintayo I (2010) The
NERICA success story: Development, achievements andlessons
learned.
Retrievedfromhttps://www.researchgate.net/profile/Soul_Kifouly_Midingo
yi/publication/265227413_The_NERICA_Success_Story_Dev
elopment_Achievements_and_Lessons_Learned/links/5788c
5ba08ae378efdda3121.pdf
Ekanayake IJ, Steponkus PL, De Datta SK (1990) Sensitivity ofpollination to water deficits at anthesis in upland rice. Crop
Sci. 30:310-315.
Fu G, Song J, Xiong J, Li Y, Chen H, Le M, Tao L (2011) Changesof oxidative stress and soluble sugar in anthers involve in ricepollen abortion under drought stress. Agr Sci China.
10:1016-1025.
Gajigo O, Denning G (2010) Rice in Africa: Will import continue
to grow? In: Dawe D (ed) The rice crisis: Markets, policies
and food security. FAO and Earthscan, Rome and London. 9.

1940

He H, Serraj R (2012) Involvement of peduncle elongation,anther dehiscence and spikelet sterility in upland rice
response to reproductive-stage drought stress. Environ Exp
Bot. 75:120-127.
Iwata-Higuchi M, Sakagami JI, Maruyama S (2019) Effect of soil
moisture stress at panicle development stage on growth andyield of upland NERICA cultivars. Trop Agr Develop.
63:140-149.
Jones MP, Dingkuhn M, Aluko GK, Semon M (1997)
Interspecific Oryza Sativa L. X O. Glaberrima Steud.
progenies in upland rice improvement. Euphytica.
92:237-246.
Kariya K, Satake T, Koike S (1985) An easy measurement ofpollen number per anther of a rice plant by a suspension
method. Jpn J Crop Sci. 54 (Extra issue 2):230-231.
Kinyumu DM (2009) Comparative study on the growth andyield of NERICA cultivated with organic and inorganic
fertilizers: Participatory on-farm research at Marakwet
district in Kenya. J Dev Sus Agr. 4:106-117.
Kobata T, Akiyama Y, Kawaoka T (2010) Convenient estimationof unfertilized grains in rice. Plant Prod Sci. 13:289-296.
Liu JX, Liao DQ, Oane R, Estenor L, Yang XE, Li ZC, Bennett J(2006) Genetic variation in the sensitivity of antherdehiscence to drought stress in rice. Field Crop Res.
97:87-100.
Matsui T, Kagata H (2003) Characteristics of floral organs
related to reliable self-pollination in rice (Oryza sativa L.).
Ann Bot-London. 91:473-477.
Matsui T, Kobayasi K, Kagata H, Horie T (2005) Correlation
between viability of pollination and length of basal
dehiscence of the theca in rice under a hot-and-humid
condition. Plant Prod Sci. 8:109-114.
Matsui T, Omasa K, Horie T (1999) Rapid swelling of pollen
grains in response to floret opening unfolds anther locules inrice (Oryza sativa L.). Plant Prod Sci. 2:196-199.
Matsushima S (1962) Some experiments on soil-water-plant
relationship in the cultivation of rice. Proc Crop Sci Soc Japan.
31:115-121.
Nassir AL, Akinade AY, Adewusi KM, Olagunju SO (2017)
Response of NERICA rice genotypes to varied soil moisturelevels and implications for drought tolerance and grain yield.
Afr J Sci Nat. 4:89-97.
Nguyen GN, Hailstones DL, Wilkes M, Sutton BG (2010) Role ofcarbohydrate metabolism in drought-induced male sterility
in rice anthers. J Agron Crop Sci. 196:346-357.

Nguyen GN, Sutton BG (2009) Water deficit reduced fertility ofyoung microspores resulting in a decline of viable maturepollen and grain set in rice. J Agron Crop Sci. 195:11-18.
Rang ZW, Jagadish SVK, Zhou QM, Craufurd PQ, Heuer S (2011)
Effect of high temperature and water stress on pollen
germination and spikelet fertility in rice. Environ Exp Bot.
70:58-65.
Saini HS, Westgate ME (1999) Reproductive development ingrain crops during drought. Adv Agron. 68:59-96.
Saragih AA, Puteh AB, Ismail MR, Mondal MMA (2013) Pollen
quality traits of cultivated (Oryza sativa L. ssp. indica) andweedy (Oryza sativa var. nivara) rice to water stress at
reproductive stage. Aust J Crop Sci. 7:1106-1112.
Satake T, Shibata M (1992) Male sterility caused by coolingtreatment at the young microspore stage in rice plants: XXXI.
Four components participating in fertilization. Jpn J Crop Sci.
61:454-462.
Sekiya N, Khatib KJ, Makame SM, Tomitaka M, Oizumi N, Araki
H (2013) Performance of a number of NERICA cultivars in
Zanzibar, Tanzania: Yield, yield components and grain quality.
Plant Prod Sci. 16:141-153.
Selote DS, Khanna-Chopra R (2004) Drought-induced spikelet
sterility is associated with an inefficient antioxidant defense
in rice panicles. Physiol Plant. 121:462-471.
Sheoran IS, Saini HS (1996) Drought-induced male sterility inrice: Changes in carbohydrate levels and enzyme activities
associated with the inhibition of starch accumulation inpollen. Sex Plant Reprod. 9:161-169.
®
Somado EA, Guei RG, Nguyen N (2008) NERICA : Origins,nomenclature and identification characteristics. In: Somado®
EA, Guei RG, Keya SO (eds) NERICA : The New Rice for Africa- A compendium. Africa Rice Center, Cotonou. 2.
Tsuboi T, Asea G, Maruyama A, Matsumoto S, Miyamoto K,
Goto A, Justin ES, Inubushi K, Ikeda R, Takagaki M, YoshimuraA, Kikuchi M (2018) Effects of rainfall, continuous cropping,and fertilizer on yield and yield components of an upland
NERICA variety: A statistical analysis of a long-term field
experiment in Uganda. Trop Agr Develop. 62:78-93.

1941