J. Agronomy & Crop Science 170, 97—102 (1993)© 1993 Paul Parey Scientific Publishers, Berlin and HamburgISSN 0931-2250

Department of Crop Science, Faculty of Agriculture,University of Peraderiiya, Peradeniya, Sri Lanka

Effect of Time of Harvest and Storage Conditionson Germination of Nutmeg {Myristica fragrans Houtt)

U. R. SANGAKKARA

Author's address: Dr. U. R. SANGAKKARA, Faculty of Agriculture, University of Peradeniya, Peradeniya,Sn Lanka.

With 3 tables

Received March 6, 1992; accepted May 4, 1992

Abstract

Nutmeg {Myristica fragrans) is a valuable tropical spice crop, which is not easily propagated vegetatively. Asthe seeds of this species lose viability soon after har\-est, storage for research causes problems, especially dueto the seasonality of production. Thus, a study evaluated the characteristics of nutmeg seeds, and therelationship between time of harvest, drying temperature, and storage condition on germinability. Seeds werepicked at full maturity, full ripeness or were collected within 2 hours after falling from the tree. Seed moisturecontents, germination characters and germination indices were determined soon after harvest. The freshlyfallen seeds were used for the drying and storage due to their better germination characters and highergermination index.

Seed moisture contents were high in the seeds. These values decreased and germinability increased withincreasing seed maturity. Germination percentages were lost at higher moisture contents at a faster rate whendried at higher temperatures. Ali seeds lost germinability at moisture contents below 45 % (dry wt basis)when dried at the selected temperatures. Germination of stored seed were maintained for a longer period oftime when stored at 5 "C in sealed transparent polythene packs, in contrast to when stored at roomtemperature. The results suggest the recalcitrant nature of nutmeg seeds and present possible methods ofstorage for short period of time while maintaining some degree of germinability.

Key words: Nutmeg, seeds, harvest time, storage, germination.

Introduction

Seed propagules of most cultivated species arestored successfully at low moisture contentsunder conditions of low humidity and temper-atures (BERJACK et al. 1984). In addition, mostspecies produce dehydrated seeds, which canbe stored under the above mentioned condi-tions. Such seeds, the longivity of which can bepredicted from moisture content and storagetemperature specifications are considered toexhibit orthodox viability characters (ROBERTS

1973), and thus are commonly termed or-thodox seeds or propagules. In contrast, there

are seeds rich in moisture and are unable towithstand dessication. These mature at hit;hmoisture contents and have little or no matura-tion drying. In addition, these propagules aredamaged by subsequent drying, thereby losingviability at high moisture contents. The seedmoisture content at which viability is lost var-ies from species to species, and possibly ac-cording to the drying regime. These are termedrecalcitrant seeds (ROBERTS 1973) and are gen-erally from tropical and subtropical treespecies (ROBERTS et al. 1984). The phenomenonof recalcitrance imposes severe limitations on

U.S. Copyright Clearance Center Code Statement: 0931-2250/93/7002-0097$02.50/0

98 SANGAKKARA

storabihty of these propagules and mostspecies thus cannot be stored for any practicalpurpose. If storage is required, wet media andwarm conditions need to be used for theserecalcitrant seeds (CORBINEAU and COME 1986).

Nutmeg (Myristica fragrans Houtt) is animportant tropical spice crop, cultivated forthe kernel of the seed and the dried aril (Mace).These products are important in the phar-maceutical, flavouring and culinary industries,and thus is a popular crop of the wet tropics(PuRSEGLOVE et al. 1981).

The seeds of nutmeg are produced as singleunits in large fruits. The seed kernel is coveredby a brittle testa. Mature seeds of nutmeg havea relatively high moisture content and cannotbe stored for long periods of time withoutlosing viability. Thus, although not confirmed,these seeds could be considered recalcitrant.

Nutmeg is generally propagated by freshseed due to their poor storability. Studies onvegetative propagation (e.g. CRUICKSHANK

1973) reported limited success of methods suchas grafting, which show problems of stock-scion relationships. Thus, although seeds arewidely used, studies do not clearly illustratethe storability of nutmeg in relation to themaintenance of seed viability, which is impor-tant in planting, breeding and selection pro-grammes (PuRSEGLOVE et al. 1981). Thus, astudy was carried out to determine the charac-teristics and germinability of freshly harvestedseed and the effect of drying and storage on themaintanance of germinability of nutmeg seeds.

Experimental Procedure

Seeds of nutmeg were obtained from similaraged trees planted on the same land, in closeproximity to the University campus. As theseeds of three maturity levels were required,fruits were picked from trees when fully ma-ture or fully ripened. The third category wasseeds picked up from under the trees withintwo hours of dehiscence.

Seeds were carefully removed from the har-vested fruit. One subsample from each type ofseed was tested gravimetrically for seed mois-ture content (dry wt basis), and another forgcrmmability. The seeds of the subsample tobe germinated were scarified mechanically atthe point of plumule emergence and planted intrays containing top soil. Three subsamples.

each containing ten seeds were used for thedetermination of seed moisture, and five sub-samples each containing 20 seeds were used forgermination. Seed germmation was evaluatedon the 60th and 65th day.

As the highest germination was observed infreshly fallen seed, further studies were carriedout with seeds of this category. The effect ofdrying temperature on seed moisture contentand germination was determined by dividingthe freshly harvested seed into three seedlots,each containing 100 seeds per drying tempera-ture. The drying temperatures were 30 °C,40 °C and 50 °C. The subsamples were dried atthe respective temperatures. Sampling was car-ried out from the three seedlots on the first dayof drying and thereafter at three day intervals.Twelve seeds were obtained from the seedlotsbeing dried at the three temperatures. Six seedswere germinated as per above method whilethe balance six were used for the determinationof seed moisture gravimetrically. This processwas carried out for a period of 25 days.

The effect of storage conditions on germina-bility of nutmeg seeds was determined usingfreshly fallen seeds. These were placed in threestorage materials, namely perforated trans-parent polythene bags, and sealed black andtransparent polythene bags (Gauge 250). Smallpackets containing 6 seeds were prepared fromeach material. These were placed at eitherroom temperature (25 °C ± 1.45 °C) or at5 °C (± 0.56 °C). Three packets of seeds fromeach packaging material were removed fromstorage at the selected temperatures at day 1and thereafter at 5 day intervals. Germinationwas determined m the manner described ear-lier. This process was continued for 40 days.

Results and Discussion

The characteristics of nutmeg seeds of differentmaturities are presented in Table 1. Theweights of nutmeg seeds decreased with in-creasing maturity. Thus, fully ripe seeds were6 % less in weight than fully mature seeds. Thefreshly fallen seed were 4 % less in weight thanthe fully ripe seed.

A comparison of seed moisture contents(dry wt basis) illustrate very high values innutmeg seeds. However, with increasing ma-turity, seed moisture contents decrease signifi-

Effect of Time of Harvest and Storage Conditions on Germination of Nutmeg 99

Table 1. Characteristics of nutmeg seeds harvested as different stages of maturity

Stage ofmaturity

Seed wt (g) % Seed moisture Time for 70 % % Final(dry wt basis) germination germination

Germinationindex

Fully matureseed

Fully ripeseed

Freshly fallenseed

LSD (P = 0.05)

15.12

14.15

13.62

0.42

66.16

60.11

58.27

1.22

66.3 days

62.5 days

54.2 days

2.44

65

75

90

2.51

1.27

1.95

9.95

cantly. The fully ripe seeds have 9 % lessmoisture than fully mature seed and freshlyfallen seed has 3 % less than fully ripe seeds.The drop in moisture content follows that ofseed weights, where a greater difference isobserved between fully mature and fully ripeseeds. However, seed moisture contents of58 % in the fallen seed is much higher thannormal values in orthodox seeds, thus indicat-ing the possibility of classifying nutmeg asrecalcitrant seed.

The data suggests an inverse relationshipbetween the stage of maturity and the timetaken for 70 % germination. Thus, with in-creasing maturity, there is a significant reduc-tion in the time taken by nutmeg to achieve70 % germination. The reduction in time tak-en for fully ripe seed to achieve 70 % germina-tion is less than both other categories. Thusstudy suggests that speed of germination in-creases with increasing maturity of nutmeg.

Final germination achieved by the three clas-ses of seeds also show that increasing maturityhas a beneficial effect on seed viability of nut-meg. Freshly fallen seed indicate greater germi-nation percentages than fully mature and fully

ripe seeds respectively. The study thus clearlyillustrates that successful germination of agreater number of seeds is obtained by usingfreshly fallen seed rather than handpicked ma-ture seed.

The germination index indicates seed vigourby considering mean daily germination and itspeak value (FARRANT et al. 1986). This parame-ter is reduced by 8 if fully ripe seed are used,and by a further 1.8 if fully mature seeds areused. Thus, the germination index also showsthe greater viabilirv^ and vigour of freshly fallenseed of nutmeg and the usefulness of theseseeds in producing planting material. The useof either fully mature or fully ripe seeds doesnot make a great difference in terms of thegermination index.

Table 2 indicates the rate of loss of seedmoisture and germinability when mature nut-meg seeds are dried at different temperatures.High temperatures reduce seed moisture con-tents and germinability more rapidly. Seedsdried at 50 °C and 40 "̂ C lost their germinabili-ty in 7 and 12 days respectively. In contrast,seeds dried at 30 °C retain some germinabilityat 15 days. The loss of geiTninability when

Table 2. Effect of drying temperature on % moisture (dry wt basis) and % germination of freshly har\^estednutmeg seeds

Drying temp °C

30

40

50

/o

/o

to

/o

/o

/o

MoistureGermination

MoistureGermination

MoistureGermination

D,

58.90

58.90

58.90

1

1

1

D

57.85

56.

60

54.

22

1

3

9

3

D

54

65

52

42

48

10

'̂

7

.1

.6

D

51

43

47

26

44

.1

.6

.8

D.

48.327

45.12

——

46.518

—

—

—

—

45.25

—

—

—

—

s.

0.872.5

0.763.2

0.348.6

100 SANGAKKARA

seeds are dried at higher temperatures can beattributed to the damage that occurs to seedtissues due to rapid removal of moisture fromthe kernel, which affects viability of seeds.

Recalcitrant seeds tend to lose germinabilitybelow a critical seed moisture content (KING

and ROBERTS 1979). This is illustrated by thedata of this study. Seeds do not show any signof germination at moisture contents below45 % (dry wt basis) irrespective of the dryingtemperature. This data again suggests the recal-citrant nature of nutmeg.

The study reveals that loss of moisture atdifferent drying temperatures affects germina-tion differently. Germination of nutmeg at amoisture content of 54 % when dried at 30°,40° and 50 °C are 65 %, 42 % and 22 % re-spectively. This shows that nutmeg seeds needto be dried as low temperatures to moisturecontents above 45 % (dry wt basis) to retainsome degree of germinability.

The effect of storage material and storagetemperature on seed germination of nutmeg ispresented in Table 3. Seeds maintain their ger-minability for a relatively longer time whenstored at 5 °C in contrast to 25 °C, irrespectiveof the storage material. This can be considereda resultant effect of the retention of seed mois-ture at the lower temperature, which is impor-tant in maintaining the germinability of recal-citrant seeds (HANSON 1984). This again sug-gests the recalcitrant nature of nutmeg seeds.In contrast, the loss of germinability of seedsstored at 25 °C, irrespective of the material,can be attributed to the loss of moisture at thishigher temperature. The trend in loss of ger-minability of nutmeg seeds stored in the differ-ent material at the two temperatures is alsosimilar. This indicates the importance of stor-

age temperature in determining the successfulstorage of nutmeg seeds, which in turn can beassociated with loss of moisture from seeds.

Seeds stored in perforated polythene losestheir germinability faster when seeds stored insealed packages. The more rapid loss of mois-ture when seeds are stored in the perforatedmaterial, especially at the higher temperaturecan be considered the causal factor for thisphenomenon. Seeds stored in sealed blackpolythene bags also lose their germinabilityfaster than seeds stored in sealed transparentpolythene packages. The heat absorption andretention capacity of black polythene, especial-ly at higher temperatures can be considered thecausal factor for this observation. However,further studies are required for confirmation ofthis phenomenon.

Seeds are best stored in sealed transparentpolythene packages. At room temperature11 7o germination is observed at 15 days, and15 % germination at 30 days, if stored at 5 °C.This suggests that for propagation purposes,nutmeg seeds which maintain viability for avery short period of time under normal condi-tions, can be successfully stored in sealedtransparent polythene packs at low tempera-tures. This offers a greater degree of flexibilityin transporting seeds, and establishing nutmeg

nurseries.

Conclusion

Recalcitrant seeds have a very high seed mois-ture content at harvesting, and they lose theirgerminability in a short period of time. Inaddition, these seeds lose their germinability athigh seed moisture levels and cannot be storedfor long periods of time without the loss of

Table 3. Effect of storage container and condition on germination of freshly fallen nutmeg seeds

Storage container

Perforated polythene

Sealed polythene bag (white)

Sealed polythene bag (black)

Temperature °C

5°C25 C

5^C25 "C

5°C25 °C

D,

91

S5

94

93

9291

Ds

67

42

8557

81

53

3612

74

29

69

18

% Germination

18

—

6211

58

04

07

—

41

—

35

—

30

—

12

—

15

—

—

—

s.2.35.9

8.46.5

4.13.8

Effect of Time of Harvest and Storage Conditions on Germination of Nutmeg 101

germinability (KING and ROBERTS 1974). Thesefeatures are illustrated by nutmeg seeds in thisstudy. Freshly fallen mature seeds have a mois-ture content of 58 % (dry wt basis), and theylose their germinability at moisture contentsbelow 45 % (dry wt basis). They are beststored at low temperatures which preventsrapid loss of sed moisture. However, germina-bility is lost after 30 days even when storedunder appropriate conditions. Thus, the dataclearly suggests the recalcitrant nature of nut-meg seeds.

Germinability and germination indices,which illustrate the usefulness of nutmeg seedsfor propagating purposes are highest in freshlyfallen seed. If drying of these seeds are re-quired, a low temperature (similar to thatunder shade) is considered appropriate toavoid rapid loss of moisture, which in turnaffects germination. If storage is required, nut-meg is best stored in sealed transparentpolythene which does not build up heat, butprotects seed from excessive moisture loss andpathogenic organisms, at low temperatures.

In terms of practical value of obtaining seed-lings of nutmeg, the study offers someguidehnes for appropriate storage of the seedwithout the loss of germinability. However,the time of successful storage without total lossof germinability is low. Thus further studies,using new techniques such as cryopreservationneeds to be carried out to determine the pos-sibilities of storing nutmeg seeds for longerperiods for germplasm, breeding and propaga-tion purposes.

Zusammenfassung

Einflufi von Erntezeit und Lagerungsbedin-gungen auf die Keimung von Muskatnufi{Myristica fragrans Houtt)

Der Muskatnuf^baum {Myristica fragrans) istein wertvolles tropisches Gewiirz, das sichnicht leicht vegetativ vermehrcn la£t. Da dieSamen dieser Art rasch ihre Keimkraft nachder Ernte verlieren, verursacht die Lagerungfiir Forschungsarbeiten Probleme, insbesonde-re im Hinblick auf die Abhangigkeit der Pro-duktion von der Saison. Es wurde daher eineUntersuchung durchgefiihrt, um charakteristi-sche Eigenschaften von Muskatnu£samen zuuntersuchen und die Beziehungen zwischen

dem Zeitpunkt der Ernte, der Trocknungstem-peratur und der Lagerungsbedingungen zurKeimfahigkeit zu bestimmen. Die Samen wur-den bei Vollreife geerntet oder innerhalb vonzwei Stunden nach dem Abfallen von den Bau-men gesammelt. Samenfeuchtigkeiten, Keimei-genschaften und Keimungswerte wurden kurznach der Ernte bestimmt. Frisch abgefalleneSamen wurden verwendet, um Trocknung undLagerung im Hinblick auf bessere Keimungsei-genschaften und hohere Kcimprozente zu un-tersuchen. Die Samenfeuchtigkeitsgehalte wa-ren zunachst hoch. Diese Werte gingen zuriickund die Keimfahigkeit nahm mit zunehmendcrSamenreife zu. Der Keimungsprozentsatz ver-ringerte sich bei hoheren Fcuchtigkeitsgehal-ten, wenn die Trocknung mit hoheren Tempc-raturen beschlcunigt wurde. Alle Samen verlo-ren lhrc Keimfahigkeit mit Feuchtigkeitsgehal-ten unterhalb von 45 % — bezogen auf Trok-kengewicht — unabhangig von den angewen-deten Trocknungstemperaturen. Die Keimfa-higkeit von gelagerten Samen wurde iiber einenlangeren Zeitraum aufrechterhalten, wenn dieSamen bei 5 °C m versiegelten transparentenPolythenpackungen im Verglcich zu einer La-gerung bei Raumtcmperatur gehalten wurden.Die Ergebnisse zeigen die schwierige Naturvon Muskatnuf^samen und weisen auf mogli-chc Methoden der Lagerung fiir kurze Peri-odcn hin, wenn ein gewisser Grad von Keimfa-higkeit gesichert werden soil.

Acknowledgements

Gratitude is expressed to Mr E. R. PIYADASA forresearch assistance, and to the University ofPeradeniya for Research funds.

References

BERJAK, P., M . DlNl, and N. W. PAMMENTER, 1984:Possible mechanisms underlying the different de-hydration responses in recalcitrant and orthodoxseeds — Dessication associated subcellular changesin propagules of Avicinnea marina. Seed Scienceand Technology 12, 365—384.

CORBINEAU, E., and D. COME, 1986: Storage ofrecalcitrant seeds from tropical species. Paper pre-sented at the 21st International Seed Congress,Brisbane, Australia, 1986, 12 pp.

102 SANGAKKARA, Effect of Time of Harvest and Storage Conditions on Germination of Nutmeg

CRUICKSHANK, A. M., 1973: Some aspects of nut-meg investigation programmes in Grenada. Pro-ceedings of a Conference on Spices, Tropical Pro-ducts Institute, London, UK, 6 pp.

FARRANT, J. M., N. W. PAMMENTER, and P. BER-

JAK, 19S6: The increasing dessication sensitivity ofrecalcitrant Avecinnia marina seeds with storagetime. Physiologia Plantarum 67, 291—298.

HANSON, J. W., 1984: The storage of seeds oftropical tree fruits. In: J. W. HOLDEN and J. T.WILLIAMS (eds.). Crop Genetic Resources, Conser-vation and Evaluation, 53—62. George Allen &:Unwin, London, UK.

KING, M . W. , and E. ROBERTS, 1979: The storage ofrecalcitrant seeds — Achievements and possibleapproaches. IPBGR, Rome, Italy, 91 pp.

PURSEGLOVE, J. W., E. G. BROWN, C . L. GREEN,

and S. J. ROBBINS, 1981: Spices. Longmans, UK,174—228.

ROBERTS, E., 1973: Predicting the storage Hfe ofseeds. Seed Science and Techology 1, 499—514.

, M. W. KING, and R. H. ELLIS, 1984: Recal-citrant seeds — Their recognition and storage. In:J. W. HoLDEN and J. T. WILLIAMS (eds.). CropGenetic Resources, Conservation and Evaluation,38—52. George Allen & Unwin, London, UK.