Tropical Grasslands-Forrajes Tropicales (2018) Vol. 6(1):26–33 26
Research Paper
Germination of tropical forage seeds stored for six years in ambient
and controlled temperature and humidity conditions in Thailand
Germinación de semilla de forrajeras tropicales durante seis años de
almacenamiento bajo condiciones ambientales y condiciones de temperatura
y humedad controladas en Tailandia
MICHAEL D. HARE1,2, NADDAKORN SUTIN2, SUPAPHAN PHENGPHET2 AND THEERACHAI SONGSIRI2
1 Faculty of Agriculture, Ubon Ratchathani University, Ubon Ratchathani, Thailand. www.ubuenglish.ubu.ac.th
2 Ubon Forage Seeds Co. Ltd., Jaeramair, Muang, Ubon Ratchathani, Thailand. www.ubonforageseeds.com/en/
Abstract
The germination performances of fresh seed lots were determined for 5 tropical forage species: Mulato II hybrid brachiaria [ Urochloa ruziziensis (syn. Brachiaria ruziziensis) x U. decumbens (syn. B. decumbens) x U. brizantha (syn.
B. brizantha)], Mombasa guinea [ Megathyrsus maximus (syn. Panicum maximum)], Tanzania guinea [ M. maximus (syn.
P. maximum)], Ubon paspalum ( Paspalum atratum) and Ubon stylo ( Stylosanthes guianensis), stored under ambient conditions in Thailand (mean monthly temperatures 23‒34 ºC; mean monthly relative humidity 40‒92%) or in a cool room (18‒20 ºC and 50% relative humidity) for up to 6 years. The first paper of this study showed all seeds, except unscarified Ubon stylo seed, were dead after a single year of storage in ambient conditions. This second paper shows that cool-room storage extended seed viability, but performance varied considerably between species. Germination percentage under laboratory conditions declined to below 50%, after 3 years storage for Mombasa guinea seed and Tanzania guinea seed, 4 years for Ubon paspalum seed and 4‒5 years for Mulato II seed. Ubon stylo seed maintained high germination for 5 years, in both cool-room storage (96%) and ambient-room storage (84%). Apparent embryo dormancy in acid-scarified Mulato II seed steadily increased with time in cool-storage and this seed had to be acid-scarified again each year at the time of germination testing to overcome dormancy. Physical dormancy of Mulato II seeds, imposed by the tightly bound lemma and palea in unscarified seed, was not overcome by length of time in cool-storage and these seeds had to be acid-scarified to induce germination. Hardseeded percentage in Ubon stylo seed remained high throughout the study and could be overcome only by acid-scarification. The difficulties of maintaining acceptable seed germination percentages when storing forage seeds in the humid tropics are discussed.
Keywords : Embryo dormancy, hardseededness, humid tropics, seed storage, seed viability.
Resumen
En Tailandia se determinó la germinación de semilla de 5 cultivares de forrajeras tropicales: Urochloa híbrido cv. Mulato II, Megathyrsus maximus cv. Mombasa, M. maximus cv. Tanzania, Paspalum atratum cv. Ubon, y Stylosanthes guianensis cv. Ubon stylo, almacenadas bajo condiciones ambientales (temperaturas promedio mensuales 23‒34 ºC; humedad relativa 40‒92%) o controladas en cuarto frío (18‒20 ºC; 50% humedad relativa) durante 6 años. Mientras en un estudio previo se encontró que bajo condiciones ambientales todas las semillas, excepto las de Ubon stylo no escarificadas con ácido, perdieron su viabilidad después de 1 año de almacenamiento, en este segundo estudio se encontró que el almacenamiento en cuarto frío prolongó su viabilidad, aunque con una alta variabilidad entre especies. La germinación bajó a <50% después de 3 años de almacenamiento para M. maximus cvs. Tanzania y Mombasa, 4 años ___________
Correspondence: Michael D. Hare, Ubon Forage Seeds Co. Ltd., Muu
1 602 Tha Bor Road, Jaeramair, Muang, Ubon Ratchathani, Thailand.
Email: michaelhareubon@gmail.com
Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)
Forage seed germination after 6-yr storage 27
para Paspalum atratum cv. Ubon y 4‒5 años para Urochloa híbrido cv. Mulato II. La semilla de S. guianensis cv. Ubon-stylo mantuvo una alta germinación durante 5 años de almacenamiento tanto en cuarto frío (96%) como bajo condiciones ambientales (85%). La dormancia del embrión en las semillas de cv. Mulato II, escarificadas con ácido, aumentó constantemente con el tiempo de almacenamiento en cuarto frío; por tanto, para romperla fue necesario escarificar la semilla con ácido nuevamente cada año en el momento de la prueba de germinación. De la misma forma, la dormancia física de las semillas del cv. Mulato II impuesta por la lemma y pálea fuertemente unidas en semillas no escarificadas con ácido, no se rompió con el tiempo de almacenamiento en cuarto frío, por lo que fue necesario escarificar con ácido para inducir la germinación. El porcentaje de semilla dura de S. guianensis cv. Ubon-stylo permaneció muy alto durante todo el estudio y la germinación solo se pudo inducir mediante escarificación con ácido. Se discuten las dificultades para mantener la germinación de las semillas y almacenar semilla de forrajeras en el trópico húmedo.
Palabras clave : Almacenamiento de semilla, dormancia del embrión, dormancia física, dureza de semilla, trópico húmedo, viabilidad.
Introduction
Mulato II and hardseededness in Ubon stylo persisted
under storage. However, embryo dormancy in Mombasa
Many tropical forage seeds produced and sold in Thailand
and Tanzania guinea grasses was overcome within 6
are stored under ambient conditions in store rooms and
months in cool-room storage (Hare et al. 2014).
shops where there is no control over temperature and
We used a commercial seed store (15 x 7 x 4 m) set at
humidity. The seeds are stored in conditions similar to those
18‒20 ºC and 50% RH. In this paper we report the
used to keep other grains for animal feed but which are not
performance of the initially tested seed lots under
required to germinate. Forage seeds are sometimes carried
prolonged cool-room storage at temperatures which were
over between years. There have been increasing concerns
higher than that used by Hopkinson and English (2005)
and reports about the declining germination quality of these
but with similar humidity.
forage seeds. In Australia, Hopkinson and English (2005)
stored tropical grass seeds in a cool-room (10 ºC and 50%
Materials and Methods
relative humidity, RH) and found that germination rates of
seeds initially with high viability remained high after 6 years
Seeds were harvested by village farmers from a number
cool-room storage. It was important for us to find the ideal
of villages in Northeast Thailand and Laos (Hare 2014) in
storage conditions in Thailand that would maintain seed
October 2010 (Ubon paspalum 5,000 kg, Mombasa
germination of our commercial forage seeds at acceptable
guinea 36,000 kg and Tanzania guinea 7,000 kg),
levels for more than 1 year.
November 2010 [Mulato II 12,000 kg: seed hand-knocked
We undertook an experiment on the germination of
from seed heads (Hare et al. 2007a)] and January 2011
commercial tropical forage seeds stored under ambient
[Mulato II 16,000 kg and Ubon stylo 6,000 kg: seed swept
conditions or under conditions of controlled temperature
from the ground (Hare et al. 2007a; 2007b)] and bulked
and humidity. Species represented were Mulato II
within species, harvesting method and season. All
[ Urochloa ruziziensis (syn. Brachiaria ruziziensis) x
harvested seeds were sun-dried to moisture levels in Table
U. decumbens (syn. B. decumbens) x U. brizantha (syn.
1, cleaned and processed and entered storage in late
B. brizantha)], Mombasa guinea [ Megathyrsus maximus
January 2011. For the experiment, Mulato II seeds (hand-
(syn. Panicum maximum)], Tanzania guinea [ M. maximus
knocked and ground-swept) and the Ubon stylo seeds
(syn. P. maximum)], Ubon paspalum ( Paspalum atratum)
were divided into two 3 kg sublots before storage; the first
and Ubon stylo ( Stylosanthes guianensis). All are com-
sublot was scarified in sulphuric acid (96% normal) for 10
mercial lines that are produced and sold in Thailand.
minutes, then washed and sun-dried to moisture levels in
The experiment commenced in January 2011.
Table 1, while the second sublot was left untreated
Germination results for the first 2 years (January 2011‒
(unscarified). All seed lots and sublots consisted of 3 kg
January 2013) were reported in a previous paper (Hare et
of seed drawn randomly from the total bulk of seed of
al. 2014). After 1 year of storage under ambient conditions,
each cultivar for the 2010/11 season, and placed into
seeds of all grasses tested were almost dead. After 2 years
separate large (100 x 50 cm) commercial polyethylene
cool-room storage (18‒20 ºC and 50% RH), germination
bags, hand-tied tightly at the top.
percentage of Mombasa guinea, Tanzania guinea and Ubon
The 3 kg bags of seeds consisting of one lot per bag
paspalum seeds had not declined. We also found that
were placed in 2 storage rooms, i.e. ambient conditions
apparent embryo dormancy and also physical dormancy in
and a cool-room (Hare et al. 2014). The ambient seed
Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)
28 M.D. Hare, N. Sutin, S. Phengphet and T. Songsiri
room was a storage shed at Ubon Ratchathani, Northeast
treatments with 3 replications. The entry means were
Thailand (15º N, 104º E), where mean monthly temper-
compared using Fisher’s protected LSD (P≤0.05).
atures were minimum 23 ºC, maximum 34 ºC and mean
monthly RH was minimum 40%, maximum 92%. The
Results
cool-room was maintained at 18‒20 ºC and 50% RH
throughout the study.
Moisture content
Seed samples were withdrawn from all storage lots in
January of each year and tested for germination and
Moisture contents of seeds stored in the cool-room varied
moisture percentage. For each germination test, 3
between 10.9 and 8.6% for the grasses and 8.3 and 5.1%
replications of 100 seeds, randomly selected from each
for Ubon stylo (Table 1). Acid-scarified Mulato II seeds
cultivar lot and sublot, were placed into covered petri
contained less moisture (9.1%) overall than untreated
dishes on filter paper wet with a 0.2% potassium nitrate
Mulato II seeds (9.8%). Mombasa guinea, Tanzania guinea
solution and placed in a germination cabinet set to provide
and Ubon paspalum seeds averaged 9.9% seed moisture in
16 h dark at 25 ºC and 8 h light at 35 ºC. The numbers of
cool-storage, similar to untreated Mulato II seeds (9.8%).
germinated seeds (normal seedlings), fresh ungerminated
Moisture level of untreated Ubon stylo seeds stored under
seeds or hard seeds, dead seeds and empty seeds were
ambient conditions was similar (5.5%) to that of untreated
Ubon stylo seeds in cool-storage (5.2%).
counted 7 and 14 days after wetting down. The
ungerminated seeds were tested using the tetrazolium
Seed germination
(TZ) assay test to determine if they were fresh
ungerminated (dormant), hard or dead.
Seeds of all grass cultivars maintained their germination for
For germination testing of acid-scarified Mulato II
2‒3 years in cool-storage before germination started to
seeds, further acid-scarification [sulphuric acid (96%
decline steadily and dead and empty seeds increased (Table
normal) for 10 minutes] was conducted at testing on half
2). After 6 years in cool storage, most seeds were either
the samples. To determine moisture percentage on each
dead [Mulato II hand-knocked (Table 2), Mombasa and
occasion, 3 samples of 10 g of seeds for each lot and
Tanzania guinea grasses (Table 3)], or had very low
sublot were weighed fresh and again after drying in an
germination [Ubon paspalum 2% (Table 3)] or had less than
oven at 130 ºC for 1 h (ISTA 1993). No seed moisture
10% germination [Mulato II ground-swept 9% (Table 2)].
levels were measured in 2017.
Only ground-swept Mulato II, that had been acid-scarified
Data from the experiment were subjected to analysis
upon entering cool-storage and acid-scarified again when
of variance using the IRRISTAT program from the
the germination test was conducted, gave a slightly better
International Rice Research Institute (IRRI). Each seed
seed germination of 15% after 6 years in storage. The
lot was analyzed separately with 7 years in storage as the
germination performance of Mulato II seeds, harvested by
Table 1. Effects of storage conditions on moisture contents of seeds of tropical forage cultivars during 2011‒2016.
Cultivar
2011
2012
2013
2014
2015
2016
Cool-room1
Mulato II ground-swept, acid-scarified3
7.5
8.5
9.9
8.0
10.1
9.6
Mulato II ground-swept, unscarified4
10.6
8.8
10.2
8.6
9.4
9.8
Mulato II hand-knocked, acid-scarified
8.9
8.6
10.0
8.3
10.2
9.8
Mulato II hand-knocked, unscarified
10.5
9.3
10.7
9.0
10.8
10.2
Mombasa guinea
10.3
9.2
10.4
9.2
10.7
9.9
Tanzania guinea
10.1
9.0
10.4
8.9
10.4
9.7
Ubon paspalum
10.4
8.9
10.3
9.5
10.9
10.4
Ubon stylo acid-scarified
8.3
7.2
8.0
6.7
8.5
7.8
Ubon stylo unscarified
5.1
5.2
5.2
5.4
5.4
5.1
Ambient-room2
Ubon stylo acid-scarified
9.3
9.25
Ubon stylo unscarified
5.1
5.2
5.8
5.7
5.4
5.5
118‒20 C and 50% RH. 2Range in mean monthly temperatures - minimum 23 ºC, maximum 34 ºC; range in mean monthly RH -
minimum 40%, maximum 92%. 3Scarified in sulphuric acid for 10 min, washed and dried. 4Not treated with acid. 5Seeds dead.
Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)
Forage seed germination after 6-yr storage 29
Table 2. Effects of cool-room storage conditions (18‒20 ºC and 50% RH) on germination of differently treated seeds of Mulato II hybrid brachiaria during 2011‒2017.
Seed treatment
2011
2012
2013
2014
2015
2016
2017
LSD (P≤0.05)
14-day germination (%)
Mulato II ground-swept, acid-scarified1
85
62
63
53
33
3
1
8.1
Mulato II ground-swept, acid-scarified,
90
90
89
84
75
42
15
8.4
more acid with test2
Mulato II ground-swept, unscarified3
5
7
7
9
9
8
7
ns
Mulato II ground-swept, unscarified,
84
75
81
79
65
40
9
8.1
acid with test
Mulato II hand-knocked, acid-scarified
70
63
68
20
19
1
0
17.9
Mulato II hand-knocked, acid-scarified,
86
82
84
62
46
8
0
13.0
more acid with test
Mulato II hand-knocked, unscarified
0
1
1
3
4
1
1
ns
Mulato II hand-knocked, unscarified,
51
75
86
61
41
3
0
10.3
acid with test
Fresh ungerminated seeds (%)
Mulato II ground-swept, acid-scarified1
11
29
27
31
42
39
14
3.6
Mulato II ground swept, acid-scarified,
8
9
8
1
5
4
1
2.2
more acid with test2
Mulato II ground-swept, unscarified3
90
89
86
81
71
12
8
11.7
Mulato II ground-swept, unscarified,
12
19
14
14
15
10
9
ns
acid with test
Mulato II hand-knocked, acid-scarified
28
25
18
12
10
5
0
3.2
Mulato II hand-knocked, acid-scarified,
10
11
10
8
4
4
0
4.5
more acid with test
Mulato II hand-knocked, unscarified
97
91
89
40
8
0
0
3.3
Mulato II hand-knocked, unscarified,
46
20
10
9
7
6
0
6.5
acid with test
Dead and empty seeds (%)
Mulato II ground-swept, acid-scarified1
4
9
10
16
25
58
85
7.3
Mulato II ground swept, acid-scarified,
2
1
3
15
20
52
84
9.1
more acid with test2
Mulato II ground-swept, unscarified3
5
4
7
10
20
48
85
5.6
Mulato II ground-swept, unscarified,
4
6
5
7
20
50
82
10.3
acid with test
Mulato II hand-knocked, acid-scarified
2
12
14
68
71
94
100
18.9
Mulato II hand-knocked, acid-scarified,
4
7
6
30
50
88
100
10.9
more acid with test
Mulato II hand-knocked, unscarified
3
8
10
57
88
97
99
5.3
Mulato II hand-knocked, unscarified,
3
5
4
30
52
91
100
10.3
acid with test
1Scarified in sulphuric acid for 10 min, washed and dried. 2Scarified with sulphuric acid before storage and again before germination testing. 3Not treated with acid.
hand-knocking, deteriorated more quickly with time in
after 2 years in cool-storage (Table 3). By the third year in
storage than that of ground-swept Mulato II seeds (Table
cool-storage (2014), the germination of these 3 cultivars had
2). After 4 years in storage, mean germination percentages
declined rapidly to low levels (Table 3) and by the sixth year
of all lots of hand-knocked Mulato II seeds were below
(2017), seeds were either dead (Mombasa and Tanzania) or
50%, but it took 5 years in cool-storage for similar results
had negligible germination (Ubon paspalum). The percent-
to be reached with ground-swept Mulato II seeds.
age of fresh ungerminated seeds for all cultivars quickly
Maximum seed germination of Mombasa guinea grass
declined after the second year in cool-storage to levels well
(68%) was reached after 1 year in cool-storage and those of
below 10% and the percentage of dead and empty seeds
Tanzania guinea grass (63%) and Ubon paspalum (85%)
increased rapidly at the same time (Table 3).
Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)
30 M.D. Hare, N. Sutin, S. Phengphet and T. Songsiri
Unscarified Ubon stylo seeds, when treated with acid
germination percentage of unscarified Ubon stylo seeds,
at germination testing, maintained high germination
treated with acid at the time of germination testing, was 3
percentages (>80%) for up to 5 years in both cool- and
times that of seeds acid-scarified following harvest (63 vs.
ambient-storage (Table 4). After 6 years in cool-storage,
21%). Unscarified Ubon stylo seeds still displayed 45%
Table 3. Effects of cool-room (18‒20 ºC and 50% RH) storage conditions on germination of seeds of Mombasa guinea grass, Tanzania guinea grass and Ubon paspalum during 2011‒2017.
Grass
2011
2012
2013
2014
2015
2016
2017
LSD (P≤0.05)
14-day germination (%)
Mombasa guinea grass
35
68
65
27
14
7
0
9.8
Tanzania guinea grass
43
56
63
30
31
12
0
11.1
Ubon paspalum
73
79
85
51
37
7
2
7.2
Fresh ungerminated seeds (%)
Mombasa guinea grass
56
24
3
2
1
0
0
10.7
Tanzania guinea grass
51
36
7
5
3
1
0
12.9
Ubon paspalum
21
14
6
5
3
2
0
4.6
Dead and empty seeds (%)
Mombasa guinea grass
8
8
32
71
85
93
100
10.4
Tanzania guinea grass
6
8
30
65
66
87
100
8.5
Ubon paspalum
6
7
9
44
60
91
98
8.8
Table 4. Effects of storage conditions on germination of seeds of Ubon stylo during 2011‒2017.
2011
2012
2013
2014
2015
2016
2017
LSD (P≤0.05)
Cool-room1
14-day germination (%)
Ubon stylo acid-scarified3
99
95
99
99
95
84
21
5.0
Ubon stylo unscarified4
15
19
23
14
21
19
14
ns
Ubon stylo unscarified, acid with test5
98
99
99
99
97
96
63
5.1
Ambient-room2
Ubon stylo acid-scarified
94
06
Ubon stylo unscarified
10
3
2
1
2
2
3
5.2
Ubon stylo unscarified, acid with test
96
87
93
89
90
84
45
10.7
Cool-room1
Hard ungerminated seeds (%)
Ubon stylo acid-scarified3
1
4
0
0
2
2
0
ns
Ubon stylo unscarified4
85
81
76
84
76
71
7
8.6
Ubon stylo unscarified, acid with test5
2
1
1
1
0
0
0
ns
Ambient-room2
Ubon stylo acid-scarified
6
06
Ubon stylo unscarified
87
88
91
91
89
82
47
3.8
Ubon stylo unscarified, acid with test
3
5
2
5
4
2
3
ns
Cool-room1
Dead seeds (%)
Ubon stylo acid-scarified3
0
1
1
1
3
14
79
5.9
Ubon stylo unscarified4
0
0
1
2
3
10
30
8.5
Ubon stylo unscarified, acid with test5
0
0
0
0
3
4
37
5.3
Ambient-room2
Ubon stylo acid-scarified
0
06
Ubon stylo unscarified
3
9
7
8
9
16
50
6.9
Ubon stylo unscarified, acid with test
1
8
5
6
6
14
52
5.6
118‒20 ºC and 50% RH. 2Range in mean monthly temperatures - minimum 23 ºC, maximum 34 ºC; range in mean monthly RH -
minimum 40%, maximum 92%. 3Scarified in sulphuric acid for 10 min, washed and dried. 4Not treated with acid. 5Scarified with sulphuric acid before germination testing. 6Seeds all dead.
Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)
Forage seed germination after 6-yr storage 31
germination after 6 years in ambient-storage, when
centages (Table 2). Dormancy in unscarified Mulato II
treated with acid at the time of germination testing. Ubon
seeds is prolonged compared with that in other Brachiaria
stylo seeds acid-scarified before entry into ambient stor-
species, where dormancy has previously been measured
age, died after 1 year, but in cool-room storage maintained
to last only 10 months in B. decumbens seeds (Grof 1968)
high germinations for 5 years (Table 4). Unscarified seeds
and up to 2 years in B. dictyoneura (now: U. humidicola)
in both cool- and ambient-storage, maintained high levels
seeds (Hopkinson et al. 1996), while dormancy is
(>70%) of hardseededness for up to 5 years (Table 4).
inconsequential in B. ruziziensis (Hopkinson et al. 1996).
Seeds of Ubon stylo maintained high germination
Discussion
percentages (>85%) for up to 5 years when stored in
ambient conditions, but only when they remained
Germination percentages of forage grass seeds stored in a
unscarified (Hare et al. 2014). This indicates that Ubon
cool-room in this study varied substantially after 3 years
stylo seeds should not be scarified following harvest, if
of storage with many below 50% (which we arbitrarily
the aim is to store them for 1 year or more under ambient
define as minimal for sowing to ensure acceptable
conditions. The situation differs in cool-storage, as Ubon
stands). The two guinea grass cultivars lost seed
stylo seeds, both acid-scarified and unscarified,
germination most rapidly to below 50% after 3 years cool-
maintained very high germination levels (>90%) for 4‒5
room storage, while Ubon paspalum seeds maintained
years. Only in the sixth year did germination levels drop,
higher germination for longer and could be kept in cool-
particularly with acid-treated seeds, but they remained at
room storage for up to 4 years before germination
levels above the low-to-zero germination levels of the
percentage dropped below 50%. The most durable grass
grasses. Hardseededness, a type of physical dormancy, in
seed was Mulato II with germination percentage
Ubon stylo seeds was not overcome during either
remaining above 50% for longer than seed of the other
ambient- or cool-room storage and unscarified seeds in
grasses when stored in the cool-room: for 5 years if seed
both storage rooms required treatment with acid each time
was harvested from the ground, but for only 4 years if
a germination test was conducted to overcome
seed was knocked out of the seed head at harvest. After 6
hardseededness.
years in cool-storage seed of all grasses was either dead
The moisture levels in grass seeds stored in the cool-
or had negligible levels of germination.
room varied little from year to year, being above 10% in
We define embryo dormancy as when seeds do not
the first, third and fifth years of storage and 9% or less in
germinate but the embryo inside the seed is viable. We
the second, fourth and sixth years of storage. Since the
determined viability using the TZ assay test as it is the
bags of seeds in the study were moved around within the
quickest test for evaluating seed viability. Embryo
large cool-room, as commercial bags of seeds were
dormancy in seeds of Mombasa and Tanzania guinea
introduced or withdrawn, possible variations in relative
grasses was overcome within 6 months in cool-room
humidity in the room might have caused these moisture
storage (Hare et al. 2014). On the other hand, acid
fluctuations. The seeds were stored in large commercial
scarification at the beginning of seed storage in 2011 was
polyethylene bags and moisture exchange may have taken
required to quickly overcome embryo dormancy of
place. Seed life may have been extended if the seeds were
Mulato II seeds, but with time in cool-room storage,
dried to levels of 8% or less following harvesting and
dormancy persisted and acid-scarified seeds had to be
placed in sealed packages to prevent moisture exchange
retreated with acid each year at the time of testing to get
(Hopkinson and English 2005). However, the purpose of
good germination. This secondary dormancy appears to
the study was to examine the life of our seed lots under
be a physical type of dormancy, similar to that imposed
commercial storage conditions (ambient- and cool-
by the tightly bound lemma and palea glumes over the
storage), so drying the seeds to very low seed moisture
caryopsis of unscarified seeds (Hare et al. 2008). In
levels and packaging them in moisture-proof bags was
unscarified Mulato II seeds, aging in cool-storage did not
considered impractical.
overcome the physical dormancy attributable to these
The results from this study and those from the first
glumes, so seeds had to be acid-scarified at the time of the
study (Hare et al. 2014) have important implications for
germination tests to achieve higher germination per-
the commercial storage and management of pasture seeds,
Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)
32 M.D. Hare, N. Sutin, S. Phengphet and T. Songsiri
particularly grasses, in the humid tropics. Ideally,
However, the quick deterioration in tropical grass seed
germination levels should be maintained above at least
germination has, to date, not limited the expansion of
60% for 12‒15 months, until seed from the next season is
areas sown to improved pasture species in Southeast Asia
ready for sale. Our first study showed that ambient-
and other humid tropical areas. Farmers may very well be
storage conditions in Thailand, even for a few months,
increasing their seed sowing rates to allow for a possible
were completely unsafe for seeds of our forage grasses,
decrease in germination. Some farmers may also conduct
with a rapid decline in germination percentage to well
their own single germination tests before sowing to
below 50% within 8 months of entering storage (Hare et
calculate seed sowing rates.
al. 2014). Typically, grass seeds in Thailand are harvested
from October to January, cleaned, processed and placed
Acknowledgments
in cool-room storage as soon as possible before the onset
of the hot humid wet season in March. With this quick
We thank Tropical Seeds LLC. for providing financial
entry into cool-room storage, satisfactory germination
support to this study and the Faculty of Agriculture, Ubon
levels (>70%) for most species are maintained prior to the
Ratchathani University for research facilities.
key seed-purchasing period (March‒October). The
exception is Tanzania guinea seed, where it is difficult to
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(Received for publication 11 September 2017; accepted 12 January 2018; published 31 January 2018)
© 2018
Tropical Grasslands-Forrajes Tropicales is an open-access journal published by International Center for Tropical Agriculture (CIAT). This work is licensed under the Creative Commons Attribution 4.0 International (CC BY 4.0) license. To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/