Tropical Grasslands-Forrajes Tropicales (2018) Vol. 6(1):26–33 26

DOI: 10.17138/TGFT(6)26-33

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/

Tropical Grasslands-Forrajes Tropicales (ISSN: 2346-3775)