Research paper
Effects of planting density on branching habit in 
common and Tartary buckwheat
Shinya KASAJIMA*, Wakana WATANABE, Maki KITADE, and Hirotake ITOH
Faculty of Bioindustry, Tokyo University of Agriculture, Yasaka 196, Abashiri, Hokkaido 099-2493, Japan
* Corresponding author: Shinya Kasajima (s3kasaji@nodai.ac.jp)
E-mail addresses: 
s3kasaji@nodai.ac.jp (SK); 49518102@nodai.ac.jp (WW); 49518032@nodai.ac.jp (MK); h-ito@nodai.ac.jp (HI)
DOI https://doi.org/10.3986/fag0030 
Received: April 24, 2023; accepted May 7, 2023. 
Keywords: branching habit, common buckwheat, flower cluster, ideotype, planting density, Tartary buckwheat
ABSTRACT
This study investigated the effects of planting density on the branching habit of common and Tartary buckwheat. A 
field experiment was conducted using a split-plot design with three replicates, comparing sparse (67 plants m−2), mod-
erate (111 plants m−2), and dense (222 plants m−2) planting densities in ‘Kitawasesoba’ (common) and ‘Manten-Kirari’ 
(Tartary) buckwheat varieties. Growth characteristics were examined at the stages of flower bud appearance, full flow-
ering, and maturity. Results revealed that planting density had no significant effect on main stem length but showed 
significant effects on the number of branches in both species. As planting density increased, the number of branches 
decreased, with Tartary buckwheat exhibiting more significant changes in response to planting density than common 
buckwheat. The number of flower clusters on branches also decreased with increasing planting density. These findings 
suggest a potential role for branching plasticity in adapting to different planting densities while maintaining stable 
yields and indicate the importance of developing ideotypes with optimal branching habits for both species. This research 
contributes to a better understanding of buckwheat ideotypes and can contribute to future breeding efforts and crop 
management practices.
Fagopyrum 40 (1): 15-21 (2023)
15
INTRODUCTION
Two species of buckwheat are mainly used for food: 
common buckwheat (Fagopyrum esculentum Moench) and 
Tartary buckwheat (F. tataricum (L.) Gaertn.). Although 
common buckwheat is grown throughout the world, 
mainly in Russia and China, Tartary buckwheat produc-
tion is primarily limited to China, Bhutan, and Nepal. Tar-
tary buckwheat seeds contain rutin, a major polyphenol, 
at levels approximately 100 times higher than that found 
in common buckwheat seeds (Kitabayashi et al., 1995a, 
b). Consequently, both common and Tartary buckwheat 
have recently gained attention due to their potential 
health benefits (Kreft et al., 2020; Kasajima, 2021).
Although common buckwheat produces abundant 
flowers, its seed set is generally low due to self-incompat-
ibility, resulting in poor seed yield (Woo et al., 2016). At 
present, the seed yield of common buckwheat in Japan is 
less than 1,000 kg ha−1. In contrast, Tartary buckwheat 
is an autogamous plant with high fertilization efficiency, 
leading to higher seed yield than common buckwheat. 
However, pre-harvest shattering, aborting loss, and 
threshing caused by combine harvester lower the seed 
yield of both common and Tartary buckwheat (Funatsuki 
et al., 2000; Morishita and Suzuki, 2017). Additional-
ly, Tartary buckwheat is more susceptible to excess soil 
moisture and salinity than common buckwheat (Matsuu-
ra et al., 2005a, b).
Buckwheat breeders have been developing varieties 
by improving plant type, including short plant height and 
determinate type, to increase yielding ability (Funatsuki 
et al., 1996; Honda et al., 2009; Morishita et al., 2013). 
Recently, a useful semi-dwarf common buckwheat line 
and a Tartary buckwheat cultivar with lodging resistance 
were developed (Shimizu et al., 2020; Morishita et al., 
2015). In terms of cultivation technique, maintaining the 
ideal plant density through effective crop management 
is crucial for stabilizing seed yield (Donald, 1963). Plant-
ing density is a critical factor that affects the agronomic 
traits and yield of both common and Tartary buckwheat 
(Matsui et al., 1974; Xiang et al., 2016; Fang et al., 2018). 
Previous research on soybeans has shown that yield re-
sponse at different planting densities is related to branch 
development, which is closely related to the ideotype of 
crops (Agudamu et al., 2016; Peng et al., 2008). Howev-
er, an understanding of the effects of planting density on 
the branching habit in these species is limited.
The objective of the present study was to investigate 
the effect of planting density on the branching habit of 
common and Tartary buckwheat. This information will 
be useful for developing optimal crop management prac-
tices and ideotypes for these important food crops.
MATERIALS AND METHODS
The present study used the leading buckwheat vari-
eties in Hokkaido, Japan, namely ‘Kitawasesoba’ and 
‘Manten-Kirari’ that were developed by the NARO Hok-
kaido Agricultural Research Center (Inuyama et al., 1994; 
Suzuki et al., 2014). The seeds of ‘Kitawasesoba’ were 
purchased from a commercial source. The cultivation was 
carried out in an unused field on a local farm, located in 
Yobito district, Abashiri, Hokkaido, which is the north-
ernmost region of Japan, from June to September 2021. 
The field had peat soil with a slightly acidic texture (pH: 
6.1). The study employed a split-plot design with three 
replicates, resulting in 18 subplots, where the main plots 
were assigned to two buckwheat species, namely, com-
mon buckwheat cv. ‘Kitawasesoba’ and Tartary buck-
wheat cv. ‘Manten-Kirari.’ The subplots were assigned to 
three planting densities, including sparse (67 plants m−2), 
moderate (111 plants m−2), and dense (222 plants m−2) 
planting. Each subplot measured 4.8 m2, consisting of 
four 4 m-long rows, spaced 1.2 m apart, and with a with-
in-row spacing of 0.3 m. Border rows were excluded from 
any investigation. The seeds were planted using seeder 
tapes (Nippon Plant Seeder Co., Ltd.) at intervals of one 
every 5 cm (sparse planting), 3 cm (moderate planting), 
and 1.5 cm (dense planting). The seeding was conducted 
manually in rows on June 10, 2021. The fertilizer was ap-
plied only as a basal dressing for all plants, at the rate of 2 
g m−2 of N, 8 g m−2 of P2O5, and 4.7 g m−2 of K2O.
The study investigated the main stem length and 
number of primary branches for 10 individuals of aver-
age growth from each plot at the stages of flower bud 
appearance and full flowering. The stage of flower bud 
appearance was defined as the day on which flower buds 
were observed in 40–50% of all plants. The stage of full 
flowering was defined as the day on which the apical in-
florescence of the main stem bloomed in 40–50% of all 
plants. Owing to the differences in flower bud appearance 
and full flowering stages between common buckwheat 
and Tartary buckwheat, the investigation was conducted 
on an intermediate date, with respective investigations 
performed on July 12 and 23, 2021. Harvesting was con-
ducted on September 3 and 6, 2021 for common and Tar-
tary buckwheat, respectively. After harvesting, 10 indi-
16
Kasajima et al. (2023): Effect of planting density on buckwheat branching
viduals of average growth from each plot were collected, 
and their main stem length, number of primary branch-
es, number of nodes on main stem, and number of flower 
clusters on the main stem and branch were measured. All 
small flower clusters were counted as one cluster. Sub-
sequently, the plant samples were examined for seed 
yield after oven-drying at 80 °C for 48 h, and threshed. 
In this study, we only investigated the seed yield of Tar-
tary buckwheat, as feeding damage by birds was observed 
in common buckwheat during the seed ripening period. 
Analysis of variance (ANOVA) was used to evaluate the 
effect of planting density on the growth and yield charac-
teristics in the present study. 
RESULTS AND DISCUSSION
Tables 1 and 2 show the main stem length and num-
ber of branches in common and Tartary buckwheat 
grown under different planting densities at the stages of 
flower bud appearance and full flowering, respectively. In 
both cases, the main stem length was significantly longer 
in common buckwheat compared to Tartary buckwheat, 
with no significant difference between planting densities. 
Conversely, the number of branches showed significant 
differences between planting densities and between the 
two species (only at the stage of flower bud appearance) 
but no significant interaction between planting density 
and species was observed. As planting density increased 
from sparse to dense, the number of branches decreased 
for both common and Tartary buckwheat. These findings 
indicate that while planting density did not significantly 
impact the main stem length, it had a significant effect 
on the number of branches at the stage of flower bud ap-
pearance.
Table 3 shows the results of the main stem length and 
number of nodes and branches in common and Tartary 
buckwheat grown under different planting densities at the 
stage of maturity. The main stem length was significantly 
shorter in common buckwheat compared to Tartary buck-
wheat, but there was no significant difference between 
planting densities. The number of nodes on the main stem 
showed significant differences between planting densities 
and between the two species. The number of branches 
also showed significant differences between planting den-
sities and between the two species. As the planting densi-
ty increased from sparse to dense, the number of branches 
decreased from 3.87 to 1.73 for common buckwheat and 
from 7.00 to 4.27 for Tartary buckwheat. There was no 
significant interaction between planting density and spe-
cies for both the length of the main stem and the num-
ber of nodes and branches. Results presented in Table 3 
show that the main stem length of Tartary buckwheat was 
shorter than that of common buckwheat until flowering, 
but it became longer at maturity. This result is consistent 
Species Planting density
Main stem 
length
(cm)
Number of  
branches
(/plant)
Common  
buckwheat 
Sparse planting 50.7 3.17
Moderate planting 51.5 2.07
Dense planting 48.8 0.87
Tartary  
buckwheat
Sparse planting 25.7 1.90
Moderate planting 31.1 1.17
Dense planting 32.0 0.13
ANOVA
Planting density ns **
species ** **
Interaction ns ns
Species Planting density
Main stem  
length
(cm)
Number of 
branches
(/plant)
Common 
buckwheat 
Sparse planting 114.9 4.13
Moderate planting 102.6 3.43
Dense planting 104.2 1.93
Tartary  
buckwheat
Sparse planting 87.7 5.00
Moderate planting 96.0 3.70
Dense planting 92.3 2.30
ANOVA
Planting density ns **
species ** ns
Interaction ns ns
* and ** represent significance at 5 and 1%, respectively. ns indi-
cates not significant
Table 1. Main stem length and number of branches in common and 
Tartary buckwheat grown under different planting densities at time 
of flower bud appearance. 
* and ** represent significance at 5 and 1%, respectively. ns indi-
cates not significant.
Table 2. Main stem length and number of branches in common and 
Tartary buckwheat grown under different planting densities at time 
of full flowering.
Fagopyrum 40 (1): 15-21 (2023)
17
with the reports by Kasajima et al. (2012) and Kasaji-
ma (2021). Furthermore, the extremely high number of 
branches (seven) in the sparsely planted Tartary buck-
wheat, compared to other planting densities, revealed 
that the effect of planting density was more significant in 
Tartary buckwheat than in common buckwheat.
Fig. 1 shows the numbers of flower clusters on the 
main stem and branches of each planting density in 
common and Tartary buckwheat. The number of flow-
er clusters on both the main stem and branches tended 
to be lower in common buckwheat compared to Tartary 
buckwheat. Tartary buckwheat is an autogamous plant 
and has been noted to have a higher yield potential than 
common buckwheat because of the ease of its seed set 
(Kasajima et al., 2021). The large number of branches and 
flower clusters also suggests that these factors contrib-
ute to its high yield. Further research is needed to exam-
ine the high-yielding traits of Tartary buckwheat from a 
Species Planting density
Main stem 
 length
(cm)
Number of nodes  
on main stem
(/plant)
Number of  
branches
(/plant)
Common 
buckwheat 
Sparse planting 132.0 13.1 3.87
Moderate planting 122.7 11.8 2.87
Dense planting 120.6 11.9 1.73
Tartary 
buckwheat
Sparse planting 162.4 20.9 7.00
Moderate planting 162.6 20.1 4.43
Dense planting 152.7 18.8 4.27
ANOVA
Planting density ns * **
species ** ** **
Interaction ns ns ns
Table 3. Main stem length and number of nodes and branches in common and Tartary buckwheat grown under different planting densities at 
the stage of maturity. 
* and ** represent significance at 5 and 1%, respectively. ns indicates not significant.
Species Planting density
Seed yield  
per plant
(g/plant)
Seed yield  
per square 
meter
(g/m2)
Tartary  
buckwheat
Sparse planting 1.79 120
Moderate planting 0.93 104
Dense planting 0.82 183
ANOVA ns ns
Table 4. Seed yield in Tartary buckwheat grown under different 
planting densities.
ns indicates that the differences among the planting densities are 
not significant (one-way ANOVA). The seed yield values per square 
meter were calculated based on the row and hill spacing for each 
planting density.
Number  
of flower clusters  
on main stem
Number  
of flower clusters  
on branches
Sparse 
planting
Moderate 
planting
Dense  
planting
Sparse 
planting
Moderate 
planting
Dense  
planting
 Common buckwheat Tartary buckwheat
45
40
35
30
25
20
15
10
5
0
N
um
be
r o
f fl
ow
er
 c
lu
st
er
s 
(/p
la
nt
)
Fig. 1. Numbers of flower clusters on main stem and branches of 
each planting density in common and Tartary buckwheat. Vertical 
bars represent standard errors based on three replicates.
18
Kasajima et al. (2023): Effect of planting density on buckwheat branching
plant type perspective. There were no considerable differ-
ences in the number of flower clusters on the main stem 
among planting densities in both common and Tartary 
buckwheat. However, the number of flower clusters on 
the branches decreased from 18.6 to 5.17 for common 
buckwheat and from 38.4 to 20.6 for Tartary buckwheat 
as the planting density increased from sparse to dense. 
Agudamu et al. (2016) defined branching plasticity in 
soybean as the ability to adapt to varying planting densi-
ties while maintaining a stable yield. This is achieved by 
controlling branch growth under dense planting condi-
tions and promoting more branches under sparse plant-
ing conditions to compensate for the reduced main stem 
yield. In Tartary buckwheat, the seed yield per plant in 
sparse planting was higher than that of moderate and 
dense planting, although the seed yield per square meter 
was the highest in dense planting (Table 4). Branching 
plasticity may also play a role in the adaptation to differ-
ent planting densities while maintaining stable yields in 
buckwheat as well. Further research is needed to explore 
the relationship between branching plasticity and yield 
stability in buckwheat cultivars.
Fig. 2 displays the harvested plants obtained from 
different planting densities of both common and Tartary 
buckwheat. Sparse planting conditions exhibited more 
branches and flower clusters compared to those grown 
under moderate and dense planting conditions, indicat-
ing a close relationship with the buckwheat ideotype. The 
numbers of flower clusters and bloomed florets are con-
sidered important factors that govern seed yield (Ujiha-
ra and Matano, 1975). Thus, the ideotype of buckwheat 
is considered a plant type with numerous branches and 
flower clusters; however, there has been limited research 
on this topic. In the past, plant types with many branches 
and flower clusters in buckwheat carried the risk of lodg-
ing. Nevertheless, with the introduction of semi-dwarf 
Fig. 2. Photograph of harvested plant of each planting density in common and Tartary buckwheat. Photograph of common buckwheat (left) 
on September 3, 2021. Photograph for Tartary buckwheat (right) on September 6, 2021.
Sparse 
planting
Moderate 
planting
Dense  
planting
Tartary buckwheat
Sparse 
planting
Moderate 
planting
Dense  
planting
Common buckwheat
Fagopyrum 40 (1): 15-21 (2023)
19
cultivars (Shimizu et al., 2020; Morishita et al., 2015), 
the risk of lodging is expected to decrease, and the need 
for research on plant types is likely to increase.
In conclusion, our study demonstrated the impact of 
planting density on the growth characteristics of com-
mon and Tartary buckwheat. The findings contribute to 
a better understanding of the ideal buckwheat plant type 
and the role of branching plasticity in adapting to various 
planting densities. This research has the potential to in-
form and support future breeding efforts and guide more 
efficient and sustainable buckwheat cultivation practices.
ACKNOWLEDGEMENTS
We thank Jinmon Co. Ltd. for providing seeds of 
‘Manten-Kirari’.
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IZVLEČEK
Vpliv gostote setve na razvejanje pri navadni in tatarski ajdi
V raziskavi so proučevali učinke gostote setve na razvejanost navadne in tatarske ajde. Poljski poskus je bil izveden 
z uporabo razdeljene ploskve s tremi ponovitvami, pri čemer so primerjali redko (67 rastlin na m2), zmerno (111 rastlin 
na m2) in gosto (222 rastlin na m2) gostoto setve pri ‚Kitawasesoba‘ ( navadna) in ‚Manten-Kirari‘ (tatarska) ajda. Rastne 
značilnosti so preverjali v fazah pojava cvetnih popkov, polnega cvetenja in zrelosti. Rezultati so pokazali, da gostota 
setve ni pomembno vplivala na dolžino glavnega stebla, vendar je pokazala pomembne učinke na število stranskih vej 
pri obeh vrstah. Z večanjem gostote setve se je število vej zmanjšalo, pri čemer je tatarska ajda pokazala pomembnejše 
spremembe glede na gostoto setve kot navadna ajda. Z večanjem gostote setve se je manjšalo tudi število socvetij na 
vejah. Te ugotovitve kažejo na potencialno vlogo plastičnosti razvejanja pri prilagajanju različnim gostotam setve ob 
ohranjanju stabilnih pridelkov in kažejo na pomen razvoja ideotipov z optimalnimi lastnostmi razvejanja za obe vrsti. 
Raziskava prispeva k boljšemu razumevanju ideotipov ajde in lahko prispeva k prihodnjim prizadevanjem za žlahtnjenje 
in način pridelovanja.
Fagopyrum 40 (1): 15-21 (2023)
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