EFFECTS OF Hydrolea zeylanica (L.) VAHL AND Pistia Stratiotes (L.) ON RICE GROWTH AND YIELD

Abstract

Two experiments were conducted to determine the effects of H. zeylanica (HYMZE) and P. stratiotes (PIIST) on rice growth and yield. HYMZE at 0, 5, 10, and 15 densities/0.16 m 2 were grown under three seeding rates (24, 48, and 72 seeds/0.16 m 2) of direct-seeded rice (DSR). Young and mature PIIST, each at 0, 5, 10, and 15 densities/0.16 m 2 , were also grown with transplanted rice (TPR). HYMZE-DSR competition was arranged in 3 x 4 factorial experiment in RCBD with five replications while young and mature PIIST-TPR competitions in simple RCBD each at five replications. Yield of DSR was reduced by 0.3, 6.2, and 6.1% at 5, 10, and 15 HYMZE densities/0.16 m 2. Yield of TPR, on the other hand, was reduced by 4.1% when young PIIST was grown at 15 densities while no reduction at 5 and 10 densities/0.16 m 2. Mature PIIST reduced yield of TPR by 4.2, 4.3, and 11.9% at 5, 10, and 15 densities/0.16 m 2 , respectively. Higher reductions on yield of TPR was observed when mature PIIST was grown throughout the crop's growth stages.

Full text

RICE-BASED BIOSYSTEMS JOURNAL (2020) 7: 19-26 19
EFFECTS OF Hydrolea zeylanica (L.) VAHL
AND Pistia Stratiotes (L.) ON RICE
GROWTH AND YIELD
Ma. Kathrine Dianne V. Cadeliña 1, Jaynalyn DG. Espiritu 1, Celynne O. Padilla 1,
Ronaldo T. Alberto 1, and Dindo King M. Donayre 2*
1Department of Crop Protection, Central Luzon State University, Science City of Muñoz, 3120 Nueva Ecija, 2Crop Pro-
tection Division, Philippine Rice Research Institute, Maligaya, Science City of Muñoz, 3119 Nueva Ecija
*Corresponding Author: dkmdonayre@philrice.gov.ph
Abstract
Two experiments were conducted to determine the effects of H. zeylanica (HYMZE) and P.
stratiotes (PIIST) on rice growth and yield. HYMZE at 0, 5, 10, and 15 densities/0.16 m2 were
grown under three seeding rates (24, 48, and 72 seeds/0.16 m2 ) of direct-seeded rice (DSR). Young
and mature PIIST, each at 0, 5, 10, and 15 densities/0.16 m2, were also grown with transplanted
rice (TPR). HYMZE-DSR competition was arranged in 3 x 4 factorial experiment in RCBD with
ve replications while young and mature PIIST-TPR competitions in simple RCBD each at ve
replications. Yield of DSR was reduced by 0.3, 6.2, and 6.1% at 5, 10, and 15 HYMZE densities/0.16
m2. Yield of TPR, on the other hand, was reduced by 4.1% when young PIIST was grown at 15
densities while no reduction at 5 and 10 densities/0.16 m2. Mature PIIST reduced yield of TPR by
4.2, 4.3, and 11.9% at 5, 10, and 15 densities/0.16 m2, respectively. Higher reductions on yield of
TPR was observed when mature PIIST was grown throughout the crop’s growth stages.
Keywords: Additive Design, Araceae, Hydrophyllaceae, NSIC Rc 222, Water Lettuce.
Introduction
Weeds are group of pests considered by Filipino
farmers as one of the limiting factors in achieving
higher yield of cultivated rice (Beltran et al., 2016;
Donayre et al., 2014; Moody et al., 1997). In a survey
conducted in 10 Asian countries, weeds ranked fourth
from lepidopterous leaf feeders, stemborers, and
brown plant hoppers as the most destructive pests
by rice farmers (Heong and Escalada, 1997). When
weeds are not controlled throughout the crop’s growth
stages, yield of rice under irrigated-lowland, rainfed-
lowland, and upland conditions could be reduced up
to 55, 74, and 96%, respectively (Ampong-Nyarko
and De Datta, 1991). Hydrolea zeylanica (L.) Vahl
and Pistia stratiotes L are Philippine weeds that could
grow, compete, and adversely affect the growth and
yield of cultivated rice.
H. zeylanica (HYMZE) of Family Hydrophyllaceae,
is a common weed of rice particularly in irrigated and
rainfed-lowland areas (Donayre et al., 2018; Fried et
al., 2017; Donayre et al., 2014; Moody et al., 2014;
Moody, 1989). It is an herb in aquatic and semi-
aquatic habitat,and has an annual or perennial life
cycle and ascending or procumbent growth habit. H.
zeylanica has the following appearance: sparingly
branched, nearly glabrous or pubescent stems; leaves
lanceolate to ovate with acute base and apex and
entire margin; and inorescence and sepals covered
with spreading viscid hairs. Its parts are also seen as:
rarely solitary, owers in terminal panicles or clusters
at branch apices; pedicel elongating after anthesis;
and calyx lobes lanceolate, pubescent or glabrous.
Its characteristics include purple-blue or deep purple-
green corolla; scarlet anthers; capsule, ovoid by the
persistent calyx lobes; and oblong to ovoid seeds with
longitudinal and transverse ridges (Pancho and Obien,
1995; Rhue-cheng and Constance, 1995; Davenport,
1988; Merrill, 1912).
In earlier times, HYMZE was only a minor
problem of rice in the country (Merrill, 1912). In
recent years, however, it has been considered one
of the major weeds of rice in irrigated and rainfed
lowland areas. Its ability to produce 1,313,000 seeds
plant-1 (average) and multiply through cut stems
resulted in re-growing and forming of new seedlings,
regrowth and reproduction of shoots in ooded or
saturated conditions, and rapid growth; making it
difcult to control in the eld (Casimero et al., 2008;
Morita et al., 2012; Fabro et al., 2005; Pancho, 1964).
In an interference study, Donayre and Endino-Tayson
FULL PAPER

Effects of Hydrolea zeylanica (L.) Vahl and Pistia stratiotes (L.)
20 RICE-BASED BIOSYSTEMS JOURNAL (2020) 7: 19-26
(2015) found out that HYMZE can signicantly
reduce the yields of the transplanted rice by 18.9,
24.7, 23.8, 35.5, 51.7, and 55.9% when its densities
were 6:6, 6:18, 6:30, 6:42, 6:60, and 6:120 (rice:weed
ratio).
P. stratiotes (PIIST) of Family Araceae, is likewise,
a weed of rice but mainly in irrigated-lowland areas
where extended periods of ooding or abundant
moisture takes place after harvest (Donayre et al.,
2018; Fried et al. 2017; Pancho and Obien, 1995).
Its genus name, Pistia, was derived from the Greek
word “Pistos,” which means watery (Bua-ngam and
Mercado, 1975). It is commonly called water lettuce
in English and kiapo/quiapo by Filipino rice farmers
(Donayre et al., 2018; Merrill, 1912). Moody et al.
(2014) described its characteristics as a free-oating,
stoloniferous, and perennial plant with long feathery
roots that bear off-shoots at the end of each stolon.
It also has leaves that are pale green, overlapping,
succulent, and covered with numerous hairs on both
sides of surfaces. Its older leaves have conspicuous,
ovoid swelling lled with spongy parenchyma on the
lower surface; and veins resembling a fan. The weed
propagates mainly by seed production or by division
of off-shoots (Bua-ngam and Mercado, 1975). Its
seeds germinate well underwater particularly at 10
cm depth while its off-shoot, that multiplies rapidly,
could divide up to 130 individuals in two months.
Thus, PIIST ourishes well in lowland rice areas
with abundant water or where presence of abundant
moisture is extended after harvest.
Conrming and deciding whether the weed is to
be controlled or not, or allowing it to grow without
compromising the yield of the crop are two of the main
reasons why knowledge on crop-weed competition is
very important. Earlier report conrmed that HYMZE
could reduce the yield of transplanted rice by as
much as 55.9% when not managed throughout the
crop’s growth (Donayre and Endino-Tayson, 2015).
However, studies conrming its negative effects on
growth and yield of direct-seeded rice are not yet
known. Likewise, the negative effect of PIIST on
growth and yield of transplanted rice is very limited.
Thus, this study determined the a) effects of HYMZE
on growth and yield of direct-seeded rice planted at
three seeding rates and b) effects of young and mature
PIIST on growth and yield of transplanted rice.
Materials and Methods
Location and Materials
Two rice-weed competition experiments
were separately conducted at the Crop Protection
Department, College of Agriculture, Central Luzon
State University (CLSU), Science City of Muñoz,
Nueva Ecija from November 2018 to February 2019.
Registered class quality of NSIC Rc 222, obtained
from the Philippine Rice Research Institute (PhilRice),
was used as the test rice variety. The variety was
selected as it is widely planted in irrigated-lowland
areas in the country. Three-day old pre-germinated
seeds for direct-seeding and 21-day old seedlings for
transplanting were prepared following the standard
recommendations of PhilRice (2007). Fresh, healthy
stems of HYMZE and off-shoots of PIIST were
collected from the elds of PhilRice. Collected weeds
were brought to the experimental area of CLSU for
replanting and regrowing in plastic boxes for one
month. The composite soil (Maligaya soil series) used
as medium for plantingwas collected from the rice
elds of CLSU.
Experimental Design
Hydrolea zeylanica
An additive experimental design was utilized
to determine the outcome of competition between
HYMZE and direct-seeded rice (DSR) (Swanton et al.,
2015). In this design, the density of HYMZE was kept
increased while leaving the density of DSR constant.
The experimental unit used was a rectangular, 0.16 m2
plastic box (length = 48 cm, width = 34 cm, depth
= 15 cm) lled with 8 kg sterilized, moist soil. Each
experimental unit was seeded equidistantly with
three-day old pre-germinated seeds of rice using
three different seeding rates (24 seeds for 40 kg ha-
1, 48 seeds for 80 kg ha-1, 72 seeds for 120 kg ha-1).
Afterwards, cut stems (with one node at the center
and 5 cm in length) of one-month old H. zeylanica
were planted at 0, 5, 10, and 15 densities/0.16 m2 . The
box, with pre-germinated seeds at different seeding
rates and cut stems of the weed, were arranged in 3
x 4 factorial experiment (factor a – three rice seeding
rates, factor b – four H. zeylanica densities) arranged
in randomized complete block design (RCBD) with
ve replications. DSR seedlings with HYMZE were
cultivated until its maturity. The plants were applied
with synthetic fertilizers at 15, 30, and 45 days after
direct-seeding at recommended rate of 90-30-60 NPK.
Water was supplied and maintained at 5 cm level until
maturity.
Pistia stratiotes L.
An additive experimental design was also utilized
to determine the outcome of competition between P.
stratiotes (PIIST) and transplanted rice (TPR). The
weed was placed in a rectangular plastic box similar
to the material used in planting HYMZE. Each box
was planted with six 23-day old seedlings at distance
of 10x10 cm. Simultaneously, two-week old young
off-shoots (spread of petals = 3 cm) and one-month
old mature off-shoots (spread of petals = 10 cm) of
PIIST were planted separately at 0, 5, 10, and 15

Effects of Hydrolea zeylanica (L.) Vahl and Pistia stratiotes (L.)
RICE-BASED BIOSYSTEMS JOURNAL (2020) 7: 19-26 21
densities/0.16 m2. The boxes, with TPR seedlings
and PIIST, were arranged in a simple RCBD with
ve replications. TPR seedlings with the weed were
grown until maturity. All plants were also nourished
with synthetic fertilizers using the same rate and time
of application as HYMZE-DSR competition. Water
was also supplied and maintained at 5 cm level until
maturity.
Data Collected
Height, number of leaves and tillers, shoot-dry
weights, and yield components (number of panicles
plant-1, number of grains panicle-1, percentage lled
spikelets plant-1, and 1,000-grain weight) of rice
were recorded. Grain yield was calculated from
yield components by Yoshida (1981). Reductions on
agronomic, yield components, and grain yield (GY)
of rice were calculated using the equation YL (%)
= [(GY0 – GY1)/GY0]*100, where, GY0 as the mean
values at 0 weed density and GY1 as the mean values
at 5, 10, and 15 weed densities, respectively. Shoot
dry weights of the two weeds were also recorded.
Statistical Analysis
Data on agronomic characteristics, yield
components, and grain yields of direct-seeded relative
to seeding rates and densities of H. zeylanica were
subjected to two-way analysis of variance (ANOVA)
using the Statistical Tool for Agricultural Research
(STAR 201). Data on transplanted rice relative to two
ages and densities of P. stratiotes, on the other hand,
were subjected to one-way ANOVA. All treatments
means were compared through Least Signicant
Difference at 5% level of signicance (Gomez and
Gomez, 1984).
Results and Discussion
Hydrolea zeylanica (L.) Vahl
Two-way analysis of variance (ANOVA) showed
no signicant interaction effects of seeding rate x
H. zeylanica (HYMZE) density on growth and yield
of direct-seeded rice (DSR) (Table 1). The main
effect of seeding rate was signicant on height per
plant, number of tillers and leaves per plant, shoot-
dry weight per plant, number of panicles per plant,
number of grains per panicle, and 1,000 grain weight
of DSR. No signicant differences were observed
on percentage of lled spikelets and grain yield/0.16
m2. Post hoc analysis showed that DSR planted at 24
seeds/0.16 m2 (40 kgha-1) signicantly had higher
means of height, number of tillers and leaves per
plant, shoot dry weight, and number of grains per
panicle than when planted at 48 (80 kgha-1) and 72
(120 kgha-1) seeds/0.16 m2 (Table 2). The advantage
of 24 seeds/0.16 m2 over the other two seeding rates
can be attributed to less intra-specic competition
between DSR plants. In studying the effects of
different seeding rates on growth of DSR, Gravois
and Helms (1992) reported that 43 kgha-1 resulted
in higher grains per panicle than 85, 128, 170, and
213 kgha-1 seeding rates. Ottis and Talbert (2005)
also reported that 57/62 seeds m-2 had higher means
of above ground biomass, number of panicles, and
panicle weight than 114/125, 229/250, and 458/500
seeds m-2. Miller et al. (1991) also observed that two
rice cultivars at 120 seeds m-2 had higher number of
spikelets panicle-1 than at 240, 360, 480, 600, and 840
seeds m-2. DSR planted at 72 seeds/0.16 m2 had high
number of panicles basin-1.
The main effect of HYMZE density, on the other
hand, was signicant on height plant-1, number of
tillers and leaves plant-1, shoot-dry weight plant-1,
and percentage of lled spikelets box-1. No signicant
differences were observed on number of panicles per
plant and f grains per panicle, 1,000 grain weight,
and grain yield/0.16 m2. Post hoc analysis showed
that height of DSR was higher at 10 and 15 HYMZE
densities than at 0 and 5 densities. Taller growth of
DSR at higher density of the weed could be a way
of plasticity in relation to competition. Although this
claim is only hypothetical due to lack of evidence,
Noda et al. (1968) observed that rice plants had
increasing height in response to increasing density
of Echinochloa crus-galli. The number of tillers and
leaves and shoot dry weight per plant of DSR were
not signicantly different at 0, 5, and 10 HYMZE
densities. Values of these parameters were signicantly
lower at 15 densities. Percentage of lled spikelets of
DSR were not signicantly different at 0, 10, and 15
HYMZE densities. Highest value was obtained at 5
densities. Meanwhile, no reductions were recorded on
the number of leaves per plant and grains per panicle,
percentage lled spikelets, and 1,000 grain weight of
DSR at 5 HYMZE densities (Table 3). However, there
were 0.8, 5.2, 1.0, and 4.7 reductions on height per
plant, number of tillers per plant, shoot dry weight per
plant, and number of panicles per plant.
Although no reductions were observed on height
per plant, percentage lled spikelets, and 1,000 grain
weight at 10 densities, reductions by 8.5, 4.5, 16.9,
5.4, and 3.6% were observed on number of tillers
and leaves per plant, shoot dry weight per plant, and
number of panicles per plant. Moreover, no reductions
were noted on height per plant, number of grains per
panicle, percentage lled spikelets, and 1,000 grain
weight of DSR at 15 densities. However, there were
14.5, 29.6, and 8.5% reduction observed in number
of tillers and leaves per plant, shoot dry weight per
plant, and number of panicles per plant. Grain yield of
direct-seeded rice was reduced by 0.3, 6.2, and 6.1%
when the weed was at 5, 10, and 15 densities.

Effects of Hydrolea zeylanica (L.) Vahl and Pistia stratiotes (L.)
22 RICE-BASED BIOSYSTEMS JOURNAL (2020) 7: 19-26
Table 1. ANOVA (P-values) for the eects of dierent seeding rates and densities of Hydrolea zeylanica on agronomic
characteristics, yield components, and grain yield of direct-seeded rice.
Factors Height
(cm plant-1)
No. of
tillers
plant-1
No. of
leaves
plant-1
Shoot dry
weight
(g plant-1)
No. of
panicles
0.16 m-2
No. of
grains
panicle-1
Filled
spikekets
(%)
1000 grain
weight
(g)
Grain yield
(g 0.16m-2)
SR .000** .000** .000** .000** .000** .000** .899ns .025* .411ns
HD .000** .000** .000** .001** .444ns .423ns .018* .645ns .1 97ns
SR x HD .887ns .076ns .188ns .499ns .585ns .658ns .960ns .891ns .425ns
SR – rice’ seeding rate, HD – H. zeylanica density; * - significant, P<.05; ** - highly significant, P<.005; ns – not significant at .05
level of significance
Table 2. Agronomic characteristics, yield components, and grain yield of direct-seeded rice as aected by dierent seeding rates
and densities of Hydrolea zeylanica.
Factors Height
(cm plant-1)
No. of
tillers
plant-1
No. of
leaves
plant-1
Shoot dry
weight
(g plant-1)
No. of
panicles
0.16 m-2
No. of
grains
panicle-1
Filled
spikekets
(%)
1000 grain
weight (g)
Grain yield
(g 0.16 m-2)
SD
24 83.8 a5.6 a24.0 a12 a65.3 c100.7a90.2 a24.3 b139.4 a
48 78 .1 b3.8 b1 7.2 b4.8 b80.0 b79.5 b89.9 a24.8 ab 140.8 a
72 74.3 c3.4 c14.9 c4.0 b90.6 a71.1 b90.0 a25.4 a145.6 a
HD
07 7. 4 b4.6 a19. 2 ab 7. 8 a82.4 a82 .4 a88.8 b24.6 a146.5 a
5 76.8 b4.3 ab 20.8 a7. 8 a78.6 a89.4 a91.7 a24.8 a146.1 a
10 81 .1 a4.2 bc 18.3 b6.5 ab 78.0 a79.4 a89.4 b25.1 a13 7.5 a
15 79.7 a3.9 c16.4 c5.5 b75.4 a83.9 a90.3 b24.7 a1 37. 6 a
* - significant, P<0.05; ** - highly significant, P<0.005; ns – not significant at .05 level of significance
Table 3. Reductions (%) on agronomic characteristics, yield components, and grain yield of direct-seeded rice as aected by
dierent densities of Hydrolea zeylanica L.
HD Height
plant-1 No. of
tillers
plant-1
No. of
leaves
plant-1
Shoot dry
weight
No. of
panicles
0.16 m-2
No. of
grains
panicle-1
Filled
spikekets
1000 grain
weight
Grain yield
0.16 m-2
0 - - - - - - - - -
50.8 5.2 -8.2 1.0 4.7 -8.6 -3.3 -1 .1 0.3
10 -4.8 8.5 4.5 16.9 5.4 3.6 -0.7 -2 .2 6.2
15 -3.0 14.5 14.5 29.6 8.5 -1.8 -1.8 -0.4 6 .1

Effects of Hydrolea zeylanica (L.) Vahl and Pistia stratiotes (L.)
RICE-BASED BIOSYSTEMS JOURNAL (2020) 7: 19-26 23
Pistia stratiotes
Simple ANOVA showed that agronomic
characteristics, yield components, and grain yield
of transplanted rice (TPR) at 5, 10, and 15 densities
of young P. stratiotes (PIIST) had no signicant
differences from samples grown without the weed.
However, there were signicant differences on the
number of tillers and leaves per plant (Table 4). TPR
plants grown at different densities of young PIIST had
less number of tillers and leaves per plant than TPR
plants at 0 density of the weed. Meanwhile, growth
and yield of TPR at different densities of mature
PIIST were signicantly different in terms number of
tillers per plant, shoot dry weight per plant, number
of panicles per plant, and percentage lled spikelets.
TPR plants grown with mature PIIST signicantly
had less of tillers per plant, shoot dry weight per
plant, number of panicles per plant, and percentage
lled spikelets than the samples planted at 0 density
of the weed. There were no signicant differences in
terms of height per plant, number of leaves per plant,
number of grains per panicle, 1,000 grain weight, and
grain yield/0.16 m2. No signicant reductions was
also noted on plant height and 1000 grain weight of
TPR plants at 5 densities, number of grains, and 1,000
grain weight at 10 densities, and 1,000 grain weight at
15 densities of young PIIST (Table 5). However, the
young stage of the weed reduced the other agronomic
and yield components of TPR plants by 0.1 to 14.5%
at 5 densities, 0.7 to 15.2% at 10 densities, and 1.5 to
28.1% at 15 densities.
Grain yield/0.16 m2 of TPR was not reduced at 5
and 10 densities of the weed. Instead, grain yield/0.16
m2 was reduced by 4.1% when young weed was at
Table 4. Agronomic characteristics, yield components, and grain yields of rice as aected by dierent densities of Pistia
stratiotes L.
PIIST
Density
Plant
height
(cm)
No. of
tillers
plant-1
No. of
leaves
plant-1
Shoot dry
weight
(g plant-1)
No. of
panicles
0.16 m-2
No. of
grains
panicle-1
Filled
spikekets
(%)
1000 grain
weight (g)
Grain yield
(g 0.162m-1)
Young
0 99.6 a9.4 a28.6 a9.6 a31.4 a84.5 a90.0 a23.6 a53.3 a
5 101.4 a8.1 b24.7 b9.6 a29.6 a81.7 a88.8 a24.3 a53.8 a
10 98.9 a8.0 b25.1 b8.8 a30.4 a88.3 a88.2 a24.1 a56.6 a
15 98 .1 a7.7 b25.2 b6.9 a30.0 a79.6 a88.5 a24.0 a51 .1 a
P .548 ns .003 ** .036 *.077 ns .734 ns .945 ns .215 ns .915 ns .958 ns
Mature
098.5 a8.9 a2 7.7 a10.2 a32.6 a61.6 a86.9 a24.1 a42.5 a
5100.4 a7.0 b23.8 a7. 8 b26.6 b75.0 a84.7 b23.6 a40.6 a
10 96.9 a6.7 b22.2 a6.5 b24.0 bc 8 7.5 a84.3 b23.4 a40.7 a
15 99.3 a6.3 b21.0 a7.1 b22.4 c86.9 a81.3 c24.3 a3 7.5 a
P .451 ns .000 ** .11 7 ns .003** .000 ** .282 ns .000 ** .437 ns .942 ns
* - significant (P<0.05), ** - highly significant (P<0.005), ns – not significant at 0.05 level of significance; means with the same letters are not significantly dierent at 0.05
level of significance using Fisher’s LSD.
Table 5. Reductions (%) on agronomic, yield components, and grain yield parameters of rice as aected by dierent densities
of Pistia stratiotes L.
PIIST
Density
Height No. of
tillers
plant-1
No. of
leaves
plant-1
Shoot dry
weight
No. of
panicles
0.16 m-2
No. of
grains
panicle-1
Filled
spikekets
1000 grain
weight
Grain yield
(g 0.16 m-2)
Young
0 0 0 0 0 0 0 0 0 0
5-1.8 14.5 13.5 0.1 5.7 3.3 1.3 -2.9 -0.8
10 0.7 15.2 12.2 8.1 3.2 -4.6 2.0 - 2 .1 -6.3
15 1.5 18.0 11.8 2 8 .1 4.5 5.7 1.7 -1.7 4 .1
Mature
0 0 0 0 0 0 0 0 0 0
5-2.0 2 1 .1 14.1 18.4 23.6 -21.9 2.5 2.2 4.3
10 1.6 24.4 20.1 20.2 35.7 -42.3 3.4 2.9 4.2
15 -0.9 28.9 24.0 31.3 30.0 -41. 2 6.4 -0.7 11.9

Effects of Hydrolea zeylanica (L.) Vahl and Pistia stratiotes (L.)
24 RICE-BASED BIOSYSTEMS JOURNAL (2020) 7: 19-26
15 densities. Mature PIIST, on the other hand, did
not reduce plant height and number of grains at 5
densities, number of grains per panicle at 10 densities;
and plant height, number of grains, and 1,000 grain
weight at 15 densities. However, it reduced the other
agronomic and yield components by 2.2 to 23.6%,
1.6 to 35.7%, and 6.4 to 31.3% when it was at 5, 10,
and 15 densities/0.16 m2. Grain yield was reduced by
4.2-11.9% when mature weed was at 5, 10, and 15
densities/0.16 m2.
Generally, reductions on grain yield of TPR were
higher with the presence of mature than young PIIST.
Mature PIIST has robust and numerous leaves and
roots, which results in more adverse effects on TPR
yield. Bua-ngam and Mercado (1976), on the othe
hand, had different results when they studied the
competitive ability of PIIST against rice. They found
that leaving 3-leaf stage of the weed throughout
the growth stages of 10-old rice plant (IR-8) at 1:5
(rice:weed) ratio resulted in reduced grain yield of the
crop by 39, 28, 11, and 9% at 0, 0.15, 0.30, and 0.45
g N/kg soil per pot. Age and variety of rice, age of the
weed, ratio of rice with the weed, rate of fertilizers
used, and size of the experimental unit are factors in
generating different results from experiments.
Deep understanding on crop-weed competition
helps conrm and decide whether a certain weed
is to be controlled or not. It can also help select an
appropriate weed control measures. The results of
this study conrmed that HYMZE, at 10-15 densities,
could reduce the yield of DSR plants by 6% when
not managed throughout the crop’s growth stages.
These suggest that control must be implemented when
HYMZE infests DSR plants at >10 densities/0.16
m2. In a research conducted by Donayre and Endino-
Tayson (2015), they also found that HYMZE could
also reduce the yield of TPR plants by 18.9, 24.7,
23.8, 35.5, 51.7, and 55.9% at rice:weed ratios of 6:6,
6:18, 6:30, 6:42, 6:60, and 6:120.
Gompertz and logistic models suggested that the
weed should be controlled within 0 to 700 growing
degree days (GDD) to achieve 100% relative grain
yield in TPR. At 0-670 GDD and 5-580 GDD,
HYMZE can reduce yield by 5 and 10%, respectively.
It is worth noting that the negative effect of HYMZE
on yield of DSR was lesser than TPR. This is possibly
due to the effect of high density of DSR as compared
with the density of TPR against HYMZE. Chauhan
(2012) pinpointed that the use of high seeding rates
can also help suppress weed growth and reduce weed
competition through rapid canopy closure. In a study
on growth response of upland Cyperus rotundus L. to
interference with DSR, Chauhan and Opeña (2012)
found that 12 and 24 rice plants per pot (equivalent
to 60 and 120 kg seeds ha-1) reduced the weed’s leaf
area by 79 and 86%, respectively. It also reduced the
shoot biomass, tuber production rate, and leaf biomass
of the weed.
In another study by Cao et al. (2007), they found
that weedy rice at 0, 5, 25, and 125 plants per m2
signicantly had poorer performance in the eld in
terms of its vegetative (plant height) and reproductive
traits (panicle and seed production) when grown with
DSR than with TPR. Other studies also showed that
shoot biomasses of Ammania baccifera L., Amaranthus
spinosus L., and Ludwigia octovalvis (Jacq.) Raven
were reduced by 94, 92, and 98% when grown with
higher seeding rates of DSR (Chauhan 2013; Chauhan
and Abugho, 2012). It was emphasized, however, that
the efcacy of using high seeding density to suppress
weed growths depends on the kind of weeds present
and the rice cultivar planted (Chauhan, 2012). For
example in a study on the effects of DSR interference
on growth of Echinochloa crus-galli (L.) Beauv. and
Cyperus iria L., it was found that DSR interference
only reduced the height of Echinochloa crus-galli (L.)
Beauv (Chauhan and Johnson, 2010).
Stem lengths of both weeds increased when
grown with more DSR plants than when grown
alone. However, crop’s interference reduced the
inorescences and shoot biomasses. Same trend of
results was also found when Ludwigia hyssopifolia
was grown with 4 and 12 DSR plants. The weed
reduced the effects of DSR interference by increasing
its leaf weight ratio, stem and leaf biomasses, and
specic stem length (Chauhan et al., 2011).
PIIST can reduce yield from 4-11% when grown
with TPR plants at 5 to 15 densities/0.16 m2. It is
remarkable that its young plantlets had less effect on
crop’s yield indicating that younger plants are less
competitive than mature ones. The lesser capability
of young PIIST can be used to take advantage on
selecting practical weed control techniques such as
planting tall rice varieties and using high-seeding rate.
Planting tall rice varieties that have vigorous growth,
good tillering capacity, and early maturing traits can
help suppress weeds (Chauhan, 2013; Chauhan, 2012;
Ampong-Nyarko and De Datta, 1991). High-density
rate, meanwhile, suppresses weeds through rapid
canopy closure.
Conclusion
This study conrmed that H. zeylanica at 10-15
densities/0.16 m2 could reduce the yield of direct-
seeded rice by 6%. Meanwhile, young and mature
P. stratiotes at 5-15 densities/0.16 m2 reduce yield
of transplanted rice by 4-11%. To achieve effective,
economical, and environmentally-sound weed
management, further researches related to ecology
and control of these weeds under eld conditions are

Effects of Hydrolea zeylanica (L.) Vahl and Pistia stratiotes (L.)
RICE-BASED BIOSYSTEMS JOURNAL (2020) 7: 19-26 25
recommended. Studies on the weeds’ growth responses
when grown with tall rice varieties in combination
with different seeding rates and fertilizer rates under
direct-seeding establishment, and growth responses to
manual and mechanical weeding technique can also
be explored.
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