Tropical Grasslands-Forrajes Tropicales (2017) Vol. 5(3):153–162 153
Research Paper
Evaluation and strategies of tolerance to water stress in Paspalum
germplasm
Evaluación y estrategias de tolerancia a estrés hídrico en germoplasma de
Paspalum
CRISTIANA DE G. PEZZOPANE1, ARTHUR G. LIMA2, PEDRO G. DA CRUZ3, TATIANE BELONI4,
ALESSANDRA P. FÁVERO5 AND PATRÍCIA M. SANTOS5
1 Centro Universitário Central Paulista - UNICEP, São Carlos, SP, Brazil www.unicep.edu.br
2 Universidade Estadual Paulista (UNESP), Rio Claro, SP, Brazil www.unesp.br
3 Embrapa Rondônia, Porto Velho, RO, Brazil www.embrapa.br/rondonia
4 Universidade Federal de São Carlos, Araras, SP, Brazil www.ufscar.br
5 Embrapa Pecuária Sudeste, São Carlos, SP, Brazil www.embrapa.br/pecuaria-sudeste
Abstract
The evaluation of genetic resources in germplasm banks of Paspalum can contribute to their use in breeding programs and for advanced research in biotechnology. This study evaluated the tolerance of 11 Paspalum accessions to abiotic stress caused by soil water deficit in a greenhouse experiment at Embrapa Pecuária Sudeste, São Carlos, state of São Paulo, Brazil. The variables analyzed were: dry biomass of green matter, dead matter and roots; leaf area; leaf water potential; number of days to lose leaf turgor (wilting); soil moisture at wilting; and number of tillers per pot. The results showed high genetic variability for all traits, not only among species but also within species, and also reflected the existence of different strategies of response and potential adaptation to water deficit events. For breeding programs, when the aim is to produce materials better adapted to the occurrence of prolonged drought, 5 accessions from this group seem to have good potential: P. malacophyllum BGP 289, P. quarinii BGP 229, P. regnellii BGP 112, P. conspersum BGP 402 and P. urvillei x P. dilatatum BGP 238. Conversely, when the goal is to select materials for short-term water stress conditions, 6 accessions stand out: P. atratum BGP 308, P. regnellii BGP 215, 248 and 397, P. dilatatum BGP
234 and P. malacophyllum BGP 293.
Keywords : Abiotic stress, genotypes, germplasm bank, water deficit.
Resumen
La evaluación de recursos genéticos en bancos de germoplasma de Paspalum constituye una gran ayuda en programas de mejoramiento genético y de investigación avanzada en biotecnología. En un experimento en macetas en Embrapa Pecuária Sudeste, São Carlos, estado de São Paulo, Brasil, se evaluó la tolerancia de 11 accesiones de varias especies de Paspalum al estrés abiótico causado por el déficit hídrico en el suelo. Las variables analizadas fueron: biomasa seca de la materia verde, materia muerta y raíces; área foliar; potencial hídrico foliar; número de días hasta la pérdida de la turgencia foliar (marchitamiento); humedad del suelo al momento del marchitamiento de las plantas; y número de brotes por planta. Los resultados mostraron tanto una alta variabilidad genética para todos los parámetros, no solo entre las especies, sino también dentro de las especies, como la existencia de diferentes estrategias de respuesta y potencial adaptación a eventos de déficit hídrico. Para los programas de fitomejoramiento, cuando el objetivo es producir materiales mejor adaptados a la sequía ___________
Correspondence: P.M. Santos, Embrapa Pecuária Sudeste, Rodovia
Washington Luiz, km 234 s/nº, Fazenda Canchim, São Carlos CEP
13560-970, SP, Brazil.
Email: patricia.santos@embrapa.br
Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)
154 C.G . Pezzopane, A.G. Lima, P.G. Cruz, T. Beloni, A.P. Fávero and P.M. Santos prolongada, las accesiones con mayor potencial fueron: P. malacophyllum BGP 289, P. quarinii BGP 229, P. regnellii BGP 112, P. conspersum BGP 402 y P. urvillei x P. dilatatum BGP 238. Por el contrario, cuando el objetivo es seleccionar materiales para condiciones de estrés hídrico de corta duración, se destacan las accesiones: P. atratum BGP 308, P. regnellii BGP 215, 248 y 397, P. dilatatum BGP 234 y P. malacophyllum BGP 293.
Palabras clave : Banco de germoplasma, déficit hídrico, estrés abiótico, genotipos.
Introduction
P. dilatatum, P. plicatulum and P. guenoarum, are used
successfully as forages (Acuña et al. 2011). The number
According to predictions from the fifth assessment report
of accessions and species conserved has been growing in
(AR5) of the Intergovernmental Panel on Climate Change
recent years, and the Germplasm Bank (GB) of Embrapa
(IPCC 2013) global temperature may increase by up to
Pecuária Sudeste contains more than 340 accessions of 49
4.8 °C by 2100, with increased variability and occurrence
different species of Paspalum, most belonging to the
of extreme events. In Brazil, a regionalized projection
informal group Plicatula.
suggests trends for increasing maximum and minimum
Batista and Godoy (2000) evaluated the dry matter
extremes of temperature and high spatial variability for
(DM) production of 217 accessions of Paspalum from the
precipitation when analyzing different emission scenarios
Paspalum GB of Embrapa Pecuária Sudeste, using
(Marengo et al. 2009). The challenges presented by the
B. decumbens and Andropogon gayanus cv. Baetí as
effects of climate change scenarios on agriculture are
controls. While 58 accessions (27%) showed DM
adaptation of production systems and mitigation of
production equal to or higher than the cultivars used as
greenhouse gas emissions.
controls, the selection and development of new cultivars
Plant breeding programs are designed to incorporate
should also take into account the plasticity in the response
relevant traits, such as high dry matter yield, high
of the genotype to specific conditions.
nutritional value and increased resistance to or tolerance
Some species of Paspalum, such as P. vaginatum
of biotic and abiotic factors into elite genetic resources,
(Shahba et al. 2014) and P. notatum (Acuña et al. 2010),
with the aim of releasing cultivars better suited to the
have characteristics of interest in relation to drought
conditions of use. Knowledge of these characteristics in
genotypes conserved in gene banks provides fundamental
tolerance. While some species have high forage value, no
information that allows the selection of appropriate
controlled experiments checking the tolerance to water stress
accessions for use both in breeding programs and in
of species like P. atratum, P. conspersum, P. dilatatum, P.
biotechnology research.
malacophyllum, P. quarinii and P. regnellii have been
The characterization of accessions conserved in
conducted. According to Zuloaga and Morrone (2003), P.
germplasm banks is essential to ensure their efficient use
malacophyllum is found from Mexico to northern Argentina,
for different purposes. For example, the study of
Paraguay, Brazil and Bolivia, at elevations from sea level to
responses of forage plants to stress caused by water deficit
3,000 m. It is found in agricultural fields, roadsides and
is of utmost importance, since moisture restriction can
woodlands. In turn, P. regnellii is distributed from the center
greatly reduce forage production and persistence of
to the south of Brazil, northeastern Argentina and eastern
pasture (Guenni et al. 2002; Melo et al. 2003; Araújo et
Paraguay. Both P. conspersum and P. regnellii are recorded
al. 2012; Volaire et al. 2014).
in forest edges or disturbed sites, in heavy clay soils which
The genus Paspalum belongs to the family Poaceae
are subject to waterlogging. Accession BGP 238 used in this
and includes several grasses with forage potential. More
study is a natural hybrid derived from a cross between
than 330 species have been identified (Zuloaga and
P. urvillei and P. dilatatum. Since P. urvillei has sexual
Morrone 2003), occurring widely in South America
reproductive behavior, it is common to observe hybrids in
(Quarín et al. 1997), including the Pampas, where the
populations where these species coexist.
grass is grazed by cattle, in particular. Nevertheless, its
This study evaluated the tolerance to soil moisture stress
use in cultivated pastures is still low in Brazil, while in
in some germplasm accessions of Paspalum, aiming at
other countries, like the USA, many species of Paspalum
identifying genes for drought-tolerance and transferring
that occur in Brazil, such as Paspalum notatum,
them to other plant families in future breeding programs.
Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)
Water stress tolerance in Paspalum 155
Materials and Methods
24 mmolc/dm3, Al 0 mmolc/dm3, CEC 66 mmolc/dm3,
base saturation 63%, sand 417 g/kg, silt 253 g/kg and clay
The experiment was conducted in a greenhouse, at
330 g/kg.
Embrapa Pecuária Sudeste, in São Carlos, state of São
Each pot was fertilized with 1.07 g N as urea, 1.4 g P
Paulo (21°57’ S, 47°50’ W; 860 m asl). We evaluated 11
as simple superphosphate, 0.53 g K as potassium chloride,
accessions of 7 distinct species of Paspalum belonging to
following the recommendations of Malavolta (1980) for
5 different informal groups. Seeds were obtained from the
experiments in pots.
germplasm bank of Embrapa Pecuária Sudeste (Table 1).
The experimental layout was an 11 (accessions) x 2
The accessions were chosen after a previous study
(water conditions) x 3 (replications) factorial in a
identified genotypes more suitable for forage production.
complete randomized block design. The 2 watering
Among these genotypes, 2 belonged to the informal
treatments were unwatered and irrigated regularly. When
botanical group Dilatata (BGP 234, Paspalum dilatatum
the plants had at least 3 tillers, irrigation of pots in the
Poir. biotype Uruguaiana and BGP 238, a natural hybrid
treatment with water stress was suspended, while
between P. urvillei Steud. and P. dilatatum), 2 to the
irrigation of pots in the control treatment continued with
group Malacophylla (BGP 289 and BGP 293, Paspalum
a daily amount of water equivalent to the air evaporative
malacophyllum Trin.), 1 to the group Plicatula (BGP 308,
demand as measured by several Piche evaporimeters
Paspalum atratum Swallen), 1 to the group Quadrifaria
located at random in the greenhouse.
(BGP 229, Paspalum quarinii Mez) and 5 to the group
Plants of particular accessions in the unwatered
Virgata (BGP 402, Paspalum conspersum Schrader and
treatment were harvested when the first leaf blade
BGP 112, 215, 248 and 397, Paspalum regnellii Mez).
displayed wilting in the predawn period, so different
Seedlings were grown on trays filled with organic
accessions
were
collected
on
different
days.
substrate Plantmax® and transplanted to pots at the 3-leaf
Concomitantly, in the same block, we collected a pot with
stage with 2 plants per pot. Pots with capacity of 8.5 L
2 plants of the same accession from the control treatment.
were filled with 7 kg sieved soil, with the following
Therefore, 2 pots were collected on each occasion for
chemical and physical characteristics: pHCaCl2 5.4, OM 25
each accession, 1 from the stressed treatment showing
g/dm3, Presin 6 mg/dm3, SO4-S 21 mg/dm3, K 1.3
symptoms of wilting and another with well-watered
mmolc/dm3, Ca 26 mmolc/dm3, Mg 14 mmolc/dm3, H+Al
plants from the control.
Table 1. Identification codes (BGP and collection), species names, collection sites and informal botanical groups of Paspalum accessions evaluated in this study.
Site code
Collection code
Species
Collection site
Botanical
(BGP)
group
112
VDBdSv 10073
P. regnellii Mez
Praia Grande - Santa Catarina - Brazil
Virgata
215
Lr 2
P. regnellii Mez
Itirapina - São Paulo - Brazil
Virgata
229
VTsDp 14220
P. quarinii Morrone &
São Miguel das Missões - Rio Grande do Sul - Quadrifaria
Zuloaga
Brazil
234
VTsDp 14251
P. dilatatum Poir.
Uruguaiana - Rio Grande do Sul - Brazil
Dilatata
biotipo Uruguaiana
238
VTsZi 14285
P. urvillei x P. dilatatum
Xangri-lá - Rio Grande do Sul - Brazil
Dilatata
248
VTsRcRm
P. regnellii Mez
Capão Alto - Santa Catarina - Brazil
Virgata
14424
289
VRcMmSv
P. malacophyllum Trin.
Aral Moreira - Mato Grosso do Sul - Brazil
Malacophylla
14582
293
VRcMmSv
P. malacophyllum Trin.
Japorã - Mato Grosso do Sul - Brazil
Malacophylla
14606
308
VRcMmSv
P. atratum Swallen
Terenos - Mato Grosso do Sul - Brazil
Plicatula
14525
397
-
P. regnellii Mez
unknown origin
Virgata
402
-
P. conspersum Schrader
unknown origin
Virgata
Collectors: Bd = I.I. Boldrini; D = M. DallÁgnol; Dp = Dario Palmieri; Lr = L.A.R. Batista; Mm = M.D. Moraes; Rc = Regina Célia de Oliveira; Rm = R. Miz; Sv = Glocimar P. da Silva; Ts = T. Souza-Chies; V = José Francisco M. Valls; Zi = F. Zilio.
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156 C.G . Pezzopane, A.G. Lima, P.G. Cruz, T. Beloni, A.P. Fávero and P.M. Santos When the plants were harvested, the following
P. regnellii BGP 215, with no significant differences
parameters were measured: leaf water potential (MPa),
among genotypes (P = 0.43).
determined in the last expanded leaf, in the pre-morning
Drying caused significant differences (P<0.0001) in leaf
period, with the aid of a psychrometer (Wescor micro-
water potential values in all accessions (Figure 1E), with no
meter Psypro model and sample chamber model C52),
significant differences among accessions (P = 0.33). In
where a microvoltmeter is connected to chambers where,
contrast, the number of tillers per pot (Figure 1F) was
after being calibrated with NaCl standard solution, 25 mm
affected differently by drying for different genotypes
diameter leaf discs are placed to be measured; green
(P<0.0001). Responses ranged from an increase in the
biomass; dead biomass; and root biomass determined after
number of tillers under water stress conditions of 19% for
each of the parts was packed in paper bags and dried in a
P. quarinii BGP 229 to a decrease of 34% in tiller numbers
circulation oven at 65 °C until reaching constant weight;
for P. malacophyllum BGP 293. There was considerable
total leaf area, measured using the LI-COR leaf area
variation among accessions in time to wilting following the
integrator, model LI-3100; days to turgor loss (wilting);
cessation of watering, with a range from 9 days for
soil moisture at wilting determined by weighing wet soil
P. regnellii BGP 215 to 22 days for P. malacophyllum BGP
and then drying to constant oven weight at 105 °C; and
289 (Figure 1G) (P<0.0001). However, most accessions
number of tillers per pot.
wilted between 17 and 22 days after watering ceased. At the
At the completion of the harvests, data were analyzed
point of wilting for all accessions, soil moisture levels were
using the PAST software (Hammer et al. 2001), using
about 12% (Figure 1H).
principal component analysis. This analysis is based on
Principal Component Analysis (PCA) was performed
grouping assessments to determine the genetic differences
to group accessions according to the variables that had
(Cruz 2006).
most influence on their responses. Figure 2A illustrates
the PCA comparing the accessions under both drought
Results
and well-watered conditions, and considering all the
variables recorded in this study. The cumulative variance
There were no significant interactions among genotypes
of the first 2 components was 73.9%. The x-axis was
and watering treatments for any of the variables. There
characterized by leaf area and the y-axis by the number of
was an increase (P<0.0001) in dry biomass of dead
tillers. Two distinct groups were formed, one consisting
material of shoots (Figure 1A) in all studied accessions
of accessions under water restriction (to the left) and the
under water restriction, especially for P. regnellii BGP
other composed of non-stressed accessions (to the right),
215, which showed 62% more dead material than the
indicating differences between the groups; water
control. There was no significant difference among
restriction was critical in changing
the main
genotypes (P = 0.09).
characteristics of plants.
Despite the lack of significant differences in green
The principal component analysis run only with
biomass between accessions (P = 0.066), there was wide
accessions under water stress, indicated that the variables
variation among accessions in response to drying
that explained best the distribution of genotypes were soil
(P<0.0001). Dry biomass of green matter of accessions
moisture on the x-axis, and dry biomass of roots on the y-
P. malacophyllum BGP 293 and P. regnellii BGP 248 was
axis (Figure 2B). The cumulative variance for the 2 axes
reduced by only 7 and 8%, respectively, as a result of
was 68.4%. In Figure 2B, accessions were grouped
moisture stress, while accessions P. regnellii BGP 215 and
BGP 112 showed decreases of 36 and 40% (Figure 1B).
according to certain characteristics in main number of
Root biomass varied among accessions (P = 0.0004) as
tillers, wilting days, leaf area, water potential and soil
did responses to drying (Figure 1C). Under irrigated
moisture. Accession P. regnellii BGP 215 stood out among
conditions, accessions P. urvillei x P. dilatatum BGP 238
other accessions by the higher dry biomass of roots,
and P. conspersum BGP 402 produced the highest root
P. malacophyllum BGP 293 by the larger leaf area,
yields, while P. malacophyllum BGP 289 and BGP 283
P. regnellii BGP 248 by the higher dry biomass of green
produced the lowest. Drying out under moisture stress
matter and soil moisture and accession P. urvillei x
produced quite variable responses in root biomass, with a
P. dilatatum BGP 238 by dry biomass of dead matter and
range from an increase of 34% in root biomass for
roots. The variable water potential grouped the accessions
P. regnellii BGP 215 to a decrease of 42% for accession
P. dilatatum BGP 234, P. regnellii BGP 397 and
P. conspersum BGP 402 . For this variable, there was no
P. atratum BGP 308, while number of tillers and days to
significant difference among treatments (P = 0.3099).
wilting determined the group formed by P. malacophyllum
Moisture stress caused a reduction (P<0.0001) in leaf
BGP 289, P. quarinii BGP 229, P. conspersum BGP 402
area (Figure 1D) in all accessions, reaching 85% in
and P. regnellii BGP 112.
Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)
Water stress tolerance in Paspalum 157
Figure 1. Mean values of the measured variables for the Paspalum accessions used in this study. Black bars indicate non-stressed plants and grey bars indicate plants under water stress. A. Dead biomass (g DM/pot); B. Green biomass (g DM/pot); C. Root biomass (g DM/pot); D. Leaf area (cm2); E. Leaf water potential (MPa); F. Number of tillers; G. Days to wilting; H. Soil moisture at wilting (%).
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158 C.G . Pezzopane, A.G. Lima, P.G. Cruz, T. Beloni, A.P. Fávero and P.M. Santos
Figure 2. A – Principal component analysis of accessions of Paspalum subjected (represented by letter D) or not (represented by letter T) to water stress. B ‒ Principal component analysis with only accessions of Paspalum subjected to water stress. Analyses were made considering all variables evaluated (dry biomass of: dead matter - DBDM, green matter - DBGM and roots - DBR; leaf area; leaf water potential; number of tillers; soil moisture at wilting; and days to wilting).
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Water stress tolerance in Paspalum 159
Discussion
water deficit demonstrated a greater allocation of
photoassimilates to the root system enabling the
This study has provided interesting data on the
exploitation of a larger volume of soil for water
comparative tolerances of a range of Paspalum accessions
absorption, maintaining hydration levels in the tissue for
to low soil moisture situations. As such it provides
longer (Baruch 1994; Casola et al. 1998). The results of
indications of which accessions might be appropriate for
biomass partitioning showed that some accessions
inclusion in breeding programs with specific aims.
invested in root biomass to a greater extent than others.
However, more real differences between accessions
The decrease in leaf water potential with decreasing soil
might exist than appear from our results. The number of
moisture (Figure 1E) was observed previously by Mattos
significant differences obtained between accessions may
et al. (2005) in Urochloa species, where the leaf water
have been limited by the low numbers of plants examined
potential reduced by a factor of 8 in U. mutica and by a
for each treatment combination as large differences in
factor of 4 in the other species studied, U. humidicola,
treatment means in some cases proved to be non-
U. decumbens and U. brizantha. The reduction in leaf
significant (P>0.05). If larger numbers of plants had been
water potential is the consequence of losing water from
included per treatment, more differences might have been
stomata, which is not compensated for by water extraction
recorded as significant.
from the soil. Osmotic adjustment is considered as a
physiological mechanism to maintain turgor at low leaf
Mechanisms of tolerance to stress by water deficit in
water potentials. The decrease in the osmotic potential, due
Paspalum
to the accumulation of sugars, organic acids and ions in the
cytosol, allows the plant to continue to absorb and
Physiological responses of plants to drought conditions
translocate water to the shoot under conditions of lower
are considered primary characteristics because they are
water availability (Bray 1997).
rapidly triggered in the presence of stress (Sherrard et al.
In this experiment, the effect of water restriction on
2009). According to Garcez Neto and Gobbi (2013), all
number of tillers varied according to genotype (Figure
effects caused by water stress lead to production loss and
1F). This result suggests a variation among Paspalum
possible adjustments should be achieved for ecological
genotypes in relation to the capacity to protect
sustainability and productivity of forage grasses grown
meristematic tissues from dehydration during periods of
in environments with eventual or permanent water
water restriction. The reduction in the number of tillers is
restrictions.
related to lower activity of cell division in the
The increase in dry biomass of dead matter in
meristematic zone, responsible for leaf initiation (Skinner
unwatered treatments was not surprising as death of plant
and Nelson 1995), which also influences the activation of
parts as a result of moisture stress is well recognized
axillary buds in the formation of new tillers, prioritizing
(Figure 1A, 1B and 1D). Mattos et al. (2005) studied 4
existing tillers (Garcez Neto and Gobbi 2013).
species of Urochloa subjected to low water availability
The ability of accessions P. quarinii BGP 229,
and observed a decrease in leaf elongation rate and
P. regnellii BGP 112, P. urvillei x P. dilatatum BGP 238
increased senescence of leaf blades for all species.
and P. malacophyllum BGP 289 to delay dehydration
Some species lose leaves as drought is intensified,
longer than others would have been partially due to the
which is known as an avoidance mechanism. This
reduction in leaf area and water potential, which would
strategy allows water savings, because the smaller leaf
have led to energy savings.
area reduces transpiration of water by the plant, favoring
the maintenance of turgor, plus some photosynthetic
Grouping and classification of Paspalum genotypes
activity and carbon gain for a longer time period (Givnish
according to tolerance to drought
1987; Lamont et al. 2002; Escudero et al. 2008).
Reduction in water loss and protection of meristems can
Among the accessions there is genetic diversity, as seen
also ensure regrowth and survival of plants when drought
in the PCA. However, there was no grouping per species
conditions occur, and thus represent a strategy that some
or per botanical group, which reflects the high genetic
plants use to tolerate drought (Volaire and Lelièvre 2001;
variability that may be present not only among species but
Munne-Bosch and Alegre 2004; Volaire et al. 2014).
also within each species of this genus. Our results suggest
Besides decreasing the production of plant biomass,
that these Paspalum accessions can be grouped according
drought can change the photoassimilate partitioning in
to response strategies to stress caused by water restriction.
plants. Studies with Urochloa and Paspalum subjected to
The first group comprised of P. regnellii BGP 215, 248
Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)
160 C.G . Pezzopane, A.G. Lima, P.G. Cruz, T. Beloni, A.P. Fávero and P.M. Santos and 397, P. malacophyllum BGP 293, P. dilatatum BGP
On the other hand, little change in root biomass (Figure
234 and P. atratum BGP 308 showed the best values in
1C), along with the other observed results, suggests that it
variables of development; the second group made up of
may use stomatal control mechanisms to reduce water
accessions P. malacophyllum BGP 289, P. quarinii BGP
loss and delay tissue dehydration.
229, P. regnellii BGP 112 and P. conspersum BGP 402
Accession P. urvillei x P. dilatatum BGP 238 behaved
were characterized by the greatest number of days to lose
similarly to accession P. regnellii BGP 215 because it also
turgor in the predawn period and genotype P. urvillei x
has high values of biomass of dead matter and roots but,
P. dilatatum BGP 238 was not grouped with the others,
unlike BGP 215, the moisture stress had a negative effect
forming a specific group. Apparently, there was no
on root biomass, with 35% reduction compared with the
correlation between collecting site and strategy used by
control (Figure 1C). Time to wilting of BGP 238 was rela-
plants to overcome water deficit.
tively long, being similar to that of genotypes that were
Accessions that stood out in terms of development
grouped by this characteristic ( P. regnellii BGP 289,
variables can be further divided into 3 subgroups:
P. quarinii BGP 229, P. regnellii BGP 112 and
P. regnellii BGP 215 (group 1); P. malacophyllum BGP
P. conspersum BGP 402; Figures 2 and 1G), but the bio-
293 (group 2); P. atratum BGP 308, P. regnellii BGP 397,
mass of green matter was higher, suggesting that this ac-
P. dilatatum BGP 234 and P. regnellii BGP 248 (group 3).
cession has good potential for use under conditions where
According to PCA and the mean values of variables
there is risk of severe drought (Figures 2 and 1B).
represented in it, accession P. regnellii BGP 215 was the
Accessions P. malacophyllum BGP 289, P. quarinii
first to wilt, despite increased root system biomass and
BGP 229, P. regnellii BGP 112 and P. conspersum BGP
reductions in leaf area. This result suggests that this
402, which were characterized by the greatest number of
accession is able to maintain productivity under mild
days to wilting (Figures 2 and 1G), presented a more
water stress by expanding the root system and exploration
conservative strategy of use of natural resources, which
of a greater volume of soil, but is not tolerant of severe
provided high tolerance to conditions of severe water
drought. Pérez-Ramos et al. (2013) found that accessions
stress. More conservative genotypes in the use of
with a more aggressive survival strategy based on
resources have smaller leaf area, maintain turgor and
increased acquisition of resources, when in deep soils,
activate osmoregulation mechanisms at the leaf blade
reduce the rate of dehydration of the meristem by
level during moderate drought, and under reduced water
deepening the root system and increasing the absorption
availability, they prioritize meristems and tips of the
of water.
roots, ensuring the recovery of plants after the elimination
Santos et al. (2013) studied forage plants of the genus
of stress (Volaire and Lelièvre 2001; Volaire et al. 2014).
Urochlo a under water stress and also observed different
This is because meristems exhibit higher osmotic
behavior among the cultivars, which presented different
adjustment than other tissues during drought (Munns et
strategies of survival. Urochloa brizantha cv. Piatã
al. 1979; Matsuda and Riazi 1981; West et al. 1990) and
decreased vegetative development, consequently reduc-
therefore have potential for regeneration when the aerial
ing production, indicating a conservative strategy,
part of the plant is dead (Van Peer et al. 2004).
lowering metabolism for its survival; U. brizantha cv.
The Paspalum accessions evaluated in this study can
Marandu presented a more aggressive strategy, which did
be categorized according to their strategies in response to
not reduce productive development, but maintained high
abiotic stress due to imposed water restriction.
productivity, which, according to the authors, promoted
Knowledge of these survival strategies, which may focus
advantages under mild stress, but under conditions of
on reduced development or maintenance of productivity,
severe stress, survival may be compromised because there
will contribute to the creation and selection of genotypes
was no reduction of metabolism.
for use in the Paspalum breeding program. This assumes
Accession P. malacophyllum BGP 293 presented a
greater importance as more severe global climate change
distinct response (Figure 1); even though wilted at 14
scenarios are forecast.
days, it maintained a relatively high leaf area and little
Under the conditions of this experiment, where the
biomass of dead matter at the time of harvest (Figures 1A
evaluation assessment was interrupted when the
and 1D). The high leaf water potential (Figure 1E)
genotype’s shoots wilted in the predawn period and no
indicates that osmotic adjustment is not among the main
recovery period was allowed, it is suggested that
mechanisms of tolerance to water stress of this genotype,
accessions be separated into 2 groups so that they can be
because early stomatal closure helps control water loss.
used in breeding programs aimed at tolerance to drought.
Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)
Water stress tolerance in Paspalum 161
For environments subjected to the occurrence of
Cruz CD. 2006. Programa Genes: Análise multivariada e
prolonged droughts, the most promising candidates
simulação. Editora UFV, Viçosa, MG, Brazil.
appear to be: P. malacophyllum BGP 289, P. quarinii
Escudero A; Mediavilla S; Heilmeier H. 2008. Leaf longevity
and drought: Avoidance of the costs and risks of early leaf
BGP 229, P. regnellii BGP 112, P. conspersum BGP 402
abscission as inferred from the leaf carbon isotopic
and P. urvillei x P. dilatatum BGP 238, as they adopt
composition. Functional Plant Biology 35:705–713. DOI:
strategies in which survival under adverse conditions is
prioritized. On the other hand, for cases of mild-moderate
Garcez Neto AF; Gobbi KF. 2013. Características morfo-
water stress, priority should be given to accessions P.
anatômicas e fisiológicas de gramíneas associadas à
atratum BGP 308, P. regnellii BGP 215, BGP 248 and
tolerância à seca. In: Souza FHD de; Matta FP; Fávero AP,
BGP 397, P. dilatatum BGP 234 and P. malacophyllum
eds. Construção de ideótipos de gramíneas para usos
BGP 293, where productivity losses during water
diversos. Embrapa, Brasília, DF, Brazil. p. 175–189.
Givnish TJ. 1987. Comparative studies of leaf form: Assessing
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Acknowledgments
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The authors are grateful to FAPESP and CAPES for
five Brachiaria species. I. Biomass production, leaf growth,
financial support.
root distribution, water use and forage quality. Plant and
Soil 243:229–241. DOI: 10.1023/A:1019956719475
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(Received for publication 10 February 2017; accepted 15 July 2017; published 30 September 2017)
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