Previous Page Table of Contents Next Page


Optimum moisture contents of seeds stored at ambient temperatures - Chai, J., Ma, R., Li, L. & Du, Y.

Jianfang Chai1*, Rongyin Ma2, Lingzhi Li2 and Yiying Du2

1 Agricultural Physics, Physiological and Biochemical Institute, Hebei Academy of Agricultural and Forestry Sciences, Shijiazhuang 050051, China

2 Food and Oil Crops Institute, Hebei Academy of Agricultural and Forestry Sciences, Shijiazhuang 050031, China

* Correspondence

Abstract

This research was conducted to determine the moisture contents that give maximum longevity to seeds stored at ambient temperatures in Shijiazhuang, China. Four or five cultivars of flax (Linum usitatissimum L), sesame (Sesamum indicum L), soybean (Glycine max Merr.) and durum wheat (Triticum durum Desf) seeds were dried to moisture contents between 0.5 and 11% (fwb), sealed in air-tight containers, and then stored for 4-5 years at temperatures fluctuating between 0 and 35°C and averaging 18°C. During storage, germination percentage declined from an initial value above 90% to as low as 0% depending on the species, cultivar and moisture content at storage. Storage at high water contents resulted in complete loss of viability within 4 years. Some drying improved the longevity of all samples, but drying to extremely low water contents resulted in reduced longevity of some cultivars of each species. The range of water contents that gave maximum survival varied between species from 7.6-9.7% for wheat to 1.8-2.5% for sesame. It is concluded that there is an optimum water content for seed storage and, for seeds with high oil contents, the value of the optimum is less than the benchmark 5% water content recommended for seed storage by the International Plant Genetic Resources Institute.

Keywords: seed longevity, seed storage, temperature, moisture content, open storage, germplasm, Glycine max, Triticum durum, Sesamum indicum, Linum usitatissimum, ultra-dry.

Introduction

Since the 1950s, many countries around the world have established national repositories for preserving the genetic diversity of crops. A goal of these genebanks is to store seeds safely and economically while maintaining high viability for many years. To achieve this goal, the International Plant Genetic Resources Institute (IPGRI) recommends that seeds be dried to about 5% water content and stored at - 18°C (IBPGR, 1976; FAO/IPGRI, 1994).

The operating costs of refrigeration create a heavy economic burden for developing countries. Often seeds are stored in rooms that lack temperature control. Under these conditions, maximum longevity can be achieved only by rigid control of the water content (IBPGR, 1985; Ellis et al., 1986). How water content should be controlled is unknown. Storage experiments conducted at 65°C showed that there was a limit to the beneficial effect of drying, and the water content at which the limit was observed varied among species according to the lipid composition (Ellis et al., 1988, 1990b). Experiments conducted at lower temperatures showed a detrimental effect of drying to very low water contents (Hu et al., 1994; Vertucci and Roos, 1990). Very little information exists on the effect of temperature fluctuations on critical moisture levels. The purpose of this study was to gain practical experience of the effect of moisture content on seed longevity when seeds are stored under fluctuating temperature conditions, such as those existing if seed storage facilities are not refrigerated. One such facility is in Shijiazhuang, China, where the yearly mean temperature is 18°C, with temperatures rising to an average maximum of 35°C in the summer and falling to an average minimum of 0°C in the winter.

Materials and methods

Four to five seed cultivars each of flax (Linum usitatissimum L.), sesame (Sesamum indicum L.), soybean (Glycine max Merr.) and durum wheat (Triticum durum Desf.) were used in the study. Seed cultivars were grown in 1989 at the Food and Oil Crops Institute (soybean and sesame), the Bashang Institute of Agricultural Sciences, Zhangjiakou District, Hebei Province (flax) and by the Crops Institute, Chinese Academy of Agricultural Sciences, Beijing (wheat). Harvested seeds were placed at -18°C until they were used in early 1990.

Table 1. Initial germination percentages of flax, sesame, soyabean and wheat cultivars harvested in 1989. The standard deviation is given for the mean of four replicates


Cultivar

Germination

Standard deviation

Flax





Nan42-13

95.5

1.4


Nan24

100

0


Baya No. 2

100

0


7618-16

99

0.5


74-21

91.5

1.7

Sesame





Jizhi No. 3

100

0


Huozhima

100

0


89-1

98.5

1.1


219

97.5

1.3

Soyabean





Jidou No. 6

99

0.8


6454

100

0


4832

100

0


3385

96.5

1.4


2132

98

1.1

Wheat





86240

93

2.5


86094

93.7

3.2


8019

94

1.5


8017

94.3

2.1


Samples of flax, sesame, soybean and wheat weighing 30, 12, 150 and 150 g, respectively, were dried to different water contents by incubating seeds at 20-25°C in jars containing equal weights of regenerated silica gel for different times ranging from 1-153 days. Once a desired quantity of water was removed, samples were sealed in aluminium boxes with a rubber gasket and kept at 20-25°C until all samples for a species were prepared. When drying was completed, all samples of a particular species were transferred to a different storage room that had no temperature control. Water contents of seeds dried to different levels were determined gravimetrically with dry weights determined by heating seeds in a ventilated oven at 103±2°C for 17±1 h (soybean, flax and sesame) or at 132±2°C for 2 h (wheat) (ISTA, 1985).

Seeds were stored for up to 5 years in a room with temperatures averaging 18°C and ranging from 0-35°C depending on the season. To evaluate changes in viability during storage, one cultivar from each species was germinated after 1 year, all cultivars were germinated after 4 years and soybean and wheat were germinated after 5 years. Seeds were germinated by placing them on filter paper that was kept wet by a 4-mm damp sponge (Chai and Ma, 1992) and incubating them for 5 days (flax, sesame, soybean) or 7 days (wheat) at 20°C (ISTA, 1985). To avoid imbibitional injury, seeds were prehydrated by placing them in a cabinet at 15°C and 92% RH for 3 days (Ellis and Roberts, 1982; Ellis et al., 1990a). Significant differences in percentage germination of soybean seeds stored at low water contents were not observed after 5 years of storage. To determine whether differences were apparent using other growth parameters, axis length (root+shoot length) after germination at 20°C was also measured at year 5. Four replicates of 25 seeds each were used in percentage germination assays and 25 axes were measured for root length.

Results and discussion

These experiments were conducted to determine the rate of deterioration of seeds stored at ambient conditions in Shijiazhuang, China. All seed cultivars had initial germination percentages greater than 90% (Table 1). Slight or no reductions in germination percentage were noted after 1 year of storage (Table 2). Significant reductions from initial germination rates were observed within each accession during 4 years of storage, but the extent of the decline was a function of the cultivar and the water content of the seeds (Table 3). One cultivar of flax (No. 7618-16) deteriorated almost completely within 4 years of storage, regardless of the water content. The reason why this seed lot deteriorated more rapidly than the others is unknown. Germination percentage did not decline appreciably within the 4-year sampling period for another cultivar of flax (Baya No. 2) and three cultivars of soybean (No. 6454, No. 2132 and Jidou No. 6) when they were stored at intermediate water contents. When re-sampled after 5 years, soybean No. 2132 and Jidou No. 6 showed significant reductions in germination percentage at all water contents, but No. 6454 retained high viability (Table 4). There appears to be no relationship between initial germination rates and the extent to which germination declined during storage (compare Table 1 with Tables 3 and 4).

Table 2. Germination percentages of a cultivar of flax, sesame, soybean and wheat stored for 1 year at ambient temperatures and different water contents. Values in parentheses represent standard deviation of the mean of four replicates

Flax mc

Baya No. 2% germ

Sesame mc

No. 219 % germ

Jizhi No. 3% germ

Huzhima % germ

Soybean mc

No. 2132 % germ

Wheat mc

86240 % germ

1.1

97(1)

0.6

97(1)

99 (1)

96 (2)

2.3

95 (3)

3.5

85 (3)

2.4

97(1)

1.8

96 (2)

no data

no data

3.3

95 (1)

4.2

93 (2)

3.1

96 (2)

2.4

91 (2)

no data

no data

4.3

96 (2)

5.8

90 (3)

4.1

95(1)

3.4

92 (3)

no data

no data

5.0

97(1)

7.6

89 (2)

6.1

96(1)

4.1

92 (2)

no data

no data

6.1

97(1)

9.8

95(1)

9.3

78 (6)

5.7

66 (5)

96 (1)

91 (1)

7.6

97(1)

11.1

65 (6)







9.8

72 (5)




Table 3. Germination percentages of flax, sesame, soybean and wheat stored for 4 years at ambient temperatures and different water contents. Values in parentheses represent standard deviation of the mean of four replicates



Cultivar

Species

Water content (% fwb)

74-21

7618-16

Baya No. 2

Nan24

Nan42-13

Flax

1.2

15

0

98

20

0

(0.1)

(4)

(-)

(1)

(3)

(-)

2.3

26

3

97

41

25

(0.2)

(4)

(1)

(1)

(4)

(5)

3.2

60

3

98

52

66

(0.2)

(4)

(1)

(2)

(3)

(3)

4.3

60

3

98

43

60

(0.2)

(5)

(4)

(1)

(6)

(5)

6.3

21

0

94

13

10

(0.3)

(7)

(-)

(4)

(2)

(7)

8.6

0

0

18

0

0

(0.6)

(-)

(-)

(3)

(-)

(-)



Cultivar



0219

89-1

Huozhima

Jizhi No. 3


Sesame

0.7

88

44

59

56


(0.2)

(1)

(4)

(1)

(4)


1.8

83

66

74

86


(0.1)

(2)

(5)

(3)

(6)


2.5

86

62

74

89


(0.3)

(4)

(6)

(4)

(2)


3.4

66

45

46

85


(0.4)

(7)

(4)

(3)

(5)


4.4

65

24

43

40


(0.4)

(6)

(3)

(4)

(4)


6.0

17

5

0

6


(0.3)

(1)

(3)

(-)

(6)




Cultivar



2132

3385

4832

6454

Jidou No. 6

Soybean

2.3

90

75

87

82

78

(0.1)

(5)

(3)

(6)

(4)

(6)

3.3

90

71

83

90

82

(0.1)

(5)

(5)

(5)

(2)

(2)

4.3

93

83

77

92

91

(0.2)

(1)

(6)

(3)

(4)

(6)

5.0

91

81

84

91

93

(0.3)

(1)

(6)

(4)

(2)

(6)

6.1

86

80

55

91

84

(0.2)

(1)

(4)

(5)

(3)

(5)

7.8

53

37

44

63

39

(0.3)

(4)

(5)

(5)

(4)

(7)

9.7

0

0

0

0

0

(0.3)

(-)

(-)

(-)

(-)

(-)



Cultivar



8017

8019

86094

86240


Wheat

3.4

69

75

72

29


(0.0)

(6)

(4)

(6)

(5)


4.3

76

77

69

54


(0.0)

(3)

(5)

(6)

(6)


5.6

74

78

75

62


(0.2)

(2)

(2)

(5)

(3)


7.6

80

79

81

66


(0.1)

(4)

(2)

(5)

(6)


9.7

73

34

72

67


(0.17)

(4)

(5)

(3)

(1)


11.0

1

0

3

0


(0.2)

(1)

(-)

(1)

(-)



Table 4. Germination % of soybean and wheat and axis length of soybean stored for 5 years at ambient temperatures and different water contents. Values in parentheses represent standard deviation of the mean of four replicates (% germination assay) and of 25 axes (axis growth assay)

Soybean


Cultivar

Water content (% fw)


2132

3385

4832

6454

Jidou No. 6

2.3 (0.1)

Germination %

81 (2)

59 (5)

80 (3)

87 (3)

70 (7)

Axis length (cm)

14.3 (0.9)

11.6 (3.3)

14.2 (1.7)

9.1 (1.2)

9.7 (0.3)

3.3 (0.1)

Germination %

86 (2)

77 (6)

72 (4)

88 (2)

86 (7)

Axis length (cm)

19.3 (1.2)

17.7 (2.6)

17.2 (0.5)

16.9 (1.2)

15.8 (1.0)

4.3 (0.2)

Germination %

87 (7)

77 (3)

82 (2)

97 (3)

82 (2)

Axis length (cm)

17.1 (1.2)

16.0 (0.9)

16.2 (1.4)

20.2 (1.1)

17.3 (0.8)

5.0 (0.3)

Germination %

68 (6)

74 (5)

83 (6)

92 (5)

79 (4)

Axis length (cm)

11.3 (1.1)

12.2 (2.2)

15.8 (1.0)

15.9 (2.5)

15.7(1.3)

6.1 (0.2)

Germination %

76 (5)

60 (7)

79 (5)

96 (4)

80 (3)

Axis length (cm)

10.1 (1.8)

6.5 (0.8)

11.0 (2.5)

14.3 (1.7)

14.0 (1.8)

7.8 (0.3)

Germination %

0 (-)

51 (6)

53 (4)

69 (5)

37 (6)

Axis length (cm)

-

6.7 (1.7)

5.6 (1.1)

6.6 (1.2)

6.9 (2.5)

9.7 (0.3)

Germination %

0 (-)

0 (-)

0 (-)

0 (-)

0 (-)

Axis length (cm)

-

-

-

-

-

Wheat


Cultivar

Water content (% fw)


8017

8019

86094

86240


2.3 (0.12)

Germination %

34 (3)

49 (5)

53 (4)

4 (4)


Axis length (cm)

3.3 (1.5)

4.9 (2.7)

5.9 (1.8)

0.6 (0.3)


3.4 (0.0)

Germination %

51 (3)

63 (2)

54 (3)

2(1)


Axis length (cm)

6.3 (3.2)

9.1 (2.2)

7.2 (2.8)

0.2 (0.1)


4.3 (0.0)

Germination %

66 (5)

57 (3)

66 (5)

7 (2)


Axis length (cm)

10.6 (2.0)

9.2 (1.4)

9.1 (3.0)

1.0 (0.6)


5.6 (0.2)

Germination %

69 (6)

66 (3)

69(1)

7 (3)


Axis length (cm)

12.1 (2.4)

9.4 (1.6)

12.3 (2.2)

0.5 (0.2)


7.6 (0.1)

Germination %

68 (4)

63 (93)

72 (3)

33 (5)


Axis length (cm)

13.7 (3.1)

11.8 (2.3)

13.1 (1.9)

2.9 (0.7)


9.7 (0.2)

Germination %

76 (5)

70 (6).

74 (3)

48 (4)


Axis length (cm)

13.5 (2.5)

13.5 (3.5)

12.2 (2.0)

5.6 (1.5)


11.0 (0.2)

Germination %

8 (2)

10 (2)

23 (6)

0


Axis length (cm)

0.6 (0.3)

0.5 (0.2)

1.4 (0.8)

-



The water content at which seeds were stored had a major effect on the final germination percentage. For most samples, maximum germination was observed when seeds were stored at a water content between 2 and 10%, with the exact range dependent on species and perhaps cultivar. When cultivars of a species were pooled, optimum water contents determined after 4 years of storage were between 1.8 and 2.5% for sesame, about 3.2% for flax, between 4.3 and 5.0% for soybean, and about 7.6% for wheat (Fig. 1). After 5 years of storage, an optimum water content was more clearly indicated at 4.3% for soybean and at 9.7% for wheat (Fig. 2).

For all samples, storage of seeds at water contents greater than the optimum resulted in much lower germination percentages than their drier counterparts. The response of seeds at suboptimal water contents was variable among cultivars and species. Germination percentages of sesame cultivar No. 219 and soybean cultivars Nos 2132 and 4832 dried to 0.7 and 2.3% water, respectively, were similar to seeds stored at 2.5 and 4.3% water, respectively (Tables 3 and 4). When evaluated in terms of axis growth, a detrimental effect was clear in all soybean cultivars stored at 2.3% water (Table 3). All wheat cultivars stored at water contents less than 7.6% water showed a slight reduction in germination percentage after 4 years' storage (Table 3) which became more pronounced after 5 years of storage (Table 4). Sensitivity to drying to very low water contents was clear in wheat No. 86240 and flax cultivars No. 74-21, Nan24 and Nan42-18 (Table 2). The effect of very dry conditions on the viability of two flax cultivars could not be determined from these experiments because deterioration was excessive (No. 7618-16) or not sufficient (Baya No. 2). Differences among species and cultivars in the rate of deterioration and the sensitivity to over-drying will be the subject of future research.

Figure 1. The effect of water content during storage on germination percentage of flax, sesame, soybean and wheat cultivars stored for 4 years at ambient temperatures in Shijiazhuang, China. Data points represent the mean germination percentage of cultivars within a species (Table 2); error bars represent the standard deviation.

Figure 2. The effect of seed water content during storage on germination percentage of soybean and wheat cultivars and on axis growth of soybean cultivars stored for 5 years at ambient temperatures in Shijiazhuang, China. Data points represent the mean values for cultivars within a species (Table 3); error bars represent the standard deviation.

The experiments presented here show accelerated deterioration of some accessions when dried to extremely low water contents. This deterioration is most probably a result of seed aging, as the reduction in germination was progressive with time (compare Table 2 with Tables 3 and 4) and seeds were preimbibed to prevent artefacts resulting from imbibitional damage. Our observations of a detrimental effect of drying contrast with storage experiments conducted at 50°C (sesame) and 65°C (flax, soybean and wheat), where detrimental effects of drying were not observed at water contents as low as 2% (sesame), 1.1% (flax), 3.3% (soybean) and 3.2% (wheat) (Ellis et al., 1986, 1988, 1990b). Experiments conducted at 65°C showed a limit to the logarithmic relationship between water content and longevity (critical moisture content) for flax and wheat at 2.7% and about 5.26%, respectively. Critical water contents reported by Ellis and colleagues are lower than the optimum water content values reported here for those species. A moisture content optimum was reported for soybean seeds stored at 35°C at 5.9% (Vertucci and Roos, 1990), a value that is considerably higher than that observed here for soybean.

Conclusions

Our results show that maximum seed viability during storage of flax, sesame, soybean and wheat at ambient temperature can be achieved only with strict control of seed water content. Storage at too high a water content always resulted in reduced germination percentage. Often, storage at low water content also resulted in reduced viability or vigour of seeds. The optimum water content varied between species. Regardless of the water content at which they were stored, most cultivars tested showed significant deterioration within 5 years of storage at ambient temperatures. The extent of the deterioration was variable between cultivars and was not related to initial germination percentage.

Acknowledgements

The authors would like to thank Dr Christina Walters, National Seed Storage Laboratory, USA for her expert assistance with the paper, and Professor Zhou Mingde for her help.

References

Chai, J. and Ma, R. (1992) Experiments on germinating bed of sponge. Studies on Hebei Agricultural Crops 4, 48-51

Ellis, R.H. and Roberts, E.H. (1982) Desiccation, rehydration, germination, imbibitional injury and longevity of pea seeds (Pisum sativum). Seed Science and Technology 10, 501-508.

Ellis, R.H., Hong, T.D. and Roberts, E.H. (1986) Logarithmic relationship between moisture content and longevity in sesame seeds. Annals of Botany 57, 499-503.

Ellis, R.H., Hong, T.D. and Roberts, E.H. (1988) A low-moisture-content limit to logarithmic relations between seed moisture content and longevity. Annals of Botany 61, 405-408.

Ellis, R.H., Hong, T.D. and Roberts, E.H. (1990a) Effect of moisture content and method of rehydration on the susceptibility of pea seeds to imbibition damage. Seed Science and Technology 18, 131-137.

Ellis, R.H., Hong, T.D., Roberts, E.H. and Tao, K.-L. (1990b) Low moisture content limits to relations between seed longevity and moisture. Annals of Botany 65, 493-504.

FAO/IPGRI (1994) Genebank Standards. Rome, Food and Agriculture Organization of the United Nations/ International Board for Plant Genetic Resources.

Hu, X., Jiang, C. and Chen, S. (1994) Studies on ultradry seed and their storage tolerance, pp 94-101 in Chen, S., Jiang, C. (Eds). Proceedings of the First National Conference on Seed Preservation. Bejing, Agricultural Scientific and Technological Publishing House of China.

IBPGR (1976) Report of IBPGR Working Group on Engineering, Design and Cost Aspects of Long-term Seed Storage Facilities. Rome, International Board for Plant Genetic Resources.

IBPGR (1985) Cost-effective Long-term Seed Stores. Rome, International Board for Plant Genetic Resources.

ISTA (1985) International rules for seed testing. Seed Science and Technology 13, 299-355.

Vertucci, C.W., and Roos, E.E. (1990) Theoretical basis of protocols for seed storage. Plant Physiology 94, 1019-1023.

© CAB INTERNATIONAL, 1998


Previous Page Top of Page Next Page