CHAPTER 41. LABIATAE

The Labiatae comprise about 3000 species of herbaceous plants and shrubs within 160 genera which provide edible roots (e.g. Coleus tuberosus Benth.), flavourings, oils and medicines. The fruits comprise one-seeded nutlets and seed storage behaviour is orthodox.

SEED DORMANCY AND GERMINATION

The seeds (nutlets) generally exhibit dormancy: promotory treatments include a low germination test temperature or pre-chilling, alternating temperatures and, possibly, light. B.R. Atwater classifies seed morphology of the non-endospermic seeds into two groups: axile foliar embryos with thin, mucilaginous seed coats; and axile foliar embryos with woody seed coats and an inner semi-permeable layer. The exocarp may persist with the seeds. See Table 17.2, Chapter 17 for more information on these categories. Detailed information on seed germination is provided in this chapter for the genera Lavandula, Mentha, Ocimum, Origanum, and Salvia. Other recommended germination test procedures and dormancy-breaking treatments are summarised in Table 41.1. In addition the algorithm below may be helpful in developing germination test procedures for the more difficult accessions and other species.

RBG Kew Wakehurst Place algorithm

The first step in the algorithm is to test seeds at constant temperatures of 16°C, 21°C and 26°C with light applied for 12h/d.

If one of these regimes does not result in full germination then the second step of the algorithm is to co-apply 7 x 10^-4 M GA₃ to the germination test substrate and test in the most successful regime determined from a comparison of the results of step one.

If this does not result in full germination then the third step of the algorithm is to chip the seeds and then test in the most successful regime determined from a comparison of the results of the steps one and two.

If this does not result in full germination then the fourth step of the algorithm is to test seeds at alternating temperatures of 23°/9°C (12h/12h) and 33°/19°C (12h/12h) with light applied for 12h/d during the period spent at the upper temperature in each cycle for both regimes: co-apply 7 x 10^-4 M GA₃ to the germination test substrate if a comparison of the results of steps one and two indicate this may be worthwhile; and chip the seeds before testing if a comparison of the results of step three with those of steps one and two indicates this may be worthwhile. Some experimentation with these conditions may be worth trying. For example, a different GA₃ concentration may be advantageous.

If full germination has not been promoted, the fifth step of the algorithm is to estimate viability using a tetrazolium test (see Chapter 11, Volume I).

If the result of the tetrazolium test indicates that the failure to achieve full germination is due to the presence of dead seeds and that one of the above regimes promoted the germination of all, or almost all, the viable seeds, then this regime is used for all subsequent germination tests. If, however, the result of the tetrazolium test indicates that dormancy has not been broken by the regime applied so far in the algorithm, then experiment with modifications to the above regimes. Clues to possible satisfactory dormancy-breaking treatments and promotory germination test environments can be obtained from the information provided for the five genera in this chapter and from Table 41.1.

TABLE 41.1 Summary of germination test recommendations for species within the Labiatae

Species and Authority

Substrate

Temperature

Duration

Additional directions

Source

Coleus blumei Benth.

TP; BP

20°/30°C; 20°C

21d

light

ISTA

TP

20°/30°C

12d

light, avoid cool temperatures

AOSA

20°/30°C

21d

light

Atwater

Galeopsis segetum Neck.

TP; BP

20°/30°C; 20°C

21d

pre-chill, scratch hard seeds

ISTA

Hyssopus officinalis L.

TP; BP

20°/30°C; 20°C

14d

light

ISTA

Leonurus cardiaca L.

TP

20°/30°C

42d

pre-chill

ISTA

Marrubium vulgare L.

TP

20°/30°C

21d

pre-chill

ISTA

TP

20°/30°C

light

M&O

TP

20°/30°C

21d

light reported to be inhibitory

Heit

Melissa officinalis L.

TP

20°/30°C; 20°C

21d

pre-chill

ISTA

TP

20°/30°C

21d

light

AOSA/Heit

Molucella laevis L.

TP; BP

20°/30°C; 20°C

21d

light, pre-chill

ISTA

TP; BP

10°/30°C

21d

light, ensure good moisture supply

AOSA

15°/30°C

4d

excise embryos

Atwater

15°/30°C

activated charcoal, pre-soak, GA, 400ppm

Atwater

Nepeta cataria L.

TP; BP

20°/30°C; 20°C

28d

pre-chill

ISTA

TP

20°/30°C

21d

ISTA

TP

20°/30°C

21d

continue test for a further 5d if (reversible)

AOSA

hard seeds have begun to imbibe

TP

20°/30°C

21d

hard seeds present

Heit

Perilla frutescens (L.) Britt.

TP; BP

20°/30°C; 20°C

21d

pre-chill

ISTA

Prunella vulgaris L.

TP

20°/30°C

M&O

Rosmarinus officinalis L.

TP

20°/30°C; 20°C

28d

ISTA

TP

15°C

28d

light

AOSA

TP

20°C

21d

Heit

Satureja hortensis L.

TP

20°/30°C

21d

ISTA

BP

20°/30°C

21d

AOSA

TP

20°C

14d

Heit

Stachys grandiflora Benth.

TP

20°C

14d

ISTA

Thymus serpyllum L.

TP; BP

20°/30°C; 15°C; 20°C

21d

light

ISTA

TP

15°C

14d

light

AOSA

Thymus vulgaris L.

TP

20°/30°C; 20°C

21d

ISTA

BP

14°C

21d

AOSA

TP

15°C

21d

Heit

LAVANDULA

L. angustifolia Mill. [L. officinalis Chaix; L. spica L.; L. vera DC.]

lavender

I. Evidence of dormancy

Lavender seeds can show considerable dormancy (3,4,7).

II. Germination regimes for non-dormant seeds

TP; BP; S: 20°C; 20°/30°C (16h/8h): 21d (ISTA)

BP: 20°/30°C (16h/8h); 20°C; 15°C: 35d (ISTA)

III. Unsuccessful dormancy-breaking treatments

Constant temperatures: 20°C in light (7)

Alternating temperatures: 10°/30°C (16h/8h) in light (7); 15°/25°C (16h/8h) in light, 28d (1)

Scarification: sulphuric acid (2)

IV. Partly-successful dormancy-breaking treatments

Alternating temperatures: 10°/30°C (16h/8h), dark (7); 20°/30°C (16h/8h) in light (3,7)

Pre-chill: 5°C, 30d, germinate at 10°/30°C (16h/8h) in light or dark (7); 3°-5°C, 7-35d (4)

Potassium nitrate: co-applied, 0.2%, at 15°/25°C (16h/8h) in light, 28d (1)

GA₃: pre-applied, 24h, 100, 1000 ppm (6); pre-applied, 500-2000 ppm (8); co-applied, 25-100 ppm (3); co-applied, 200 ppm, at 10°/30°C (16h/8h) in light or 20°C in light (3); co-applied, 400 ppm (3); co-applied, 200 ppm, plus pre-chill, 3°-5°C, 7-35d (4); co-applied, 100 ppm, at 20°/30°C, 10°/30°C (16h/8h) in light (7); co-applied, 100, 200 ppm, at 10°/25°C (16h/8h) in light (7); co-applied, 400 ppm, at 15°/25°C (16h/8h) in light, 28d (1)

Fusicoccin: pre-applied, 24h, 5 ppm (6)

Ultrasonics: 830 kc, then GA₃, co-applied, 10 ppm (2)

V. Successful dormancy-breaking treatments

Pre-chill, GA₃ (ISTA)

GA₃: co-applied, 200 ppm, at 20°/30°C (16h/8h) in light, 2 W m^-2 (3,4); co-applied, 200 ppm, at 20°/30°C (16h/8h) in light or at 20°C in light (7)

VI. Comment

The following procedure has been reported to break dormancy completely in seeds of L. angustifolia: test for germination in an alternating temperature regime of 20°/30°C (16h/8h) with light applied at 2 W cm^-2 (at the seed surface) for 8 hours per day during the higher temperature phase of each diurnal cycle with GA₃ co-applied at 200 ppm (3,4,7). A 56 day, or longer, test may be necessary. Since some accessions may contain large numbers of empty seeds it has been suggested that all non-germinated seed-like structures be dissected at the end of each germination test (5).

VII. References

1. Atwater, B.R. (1980). Germination, dormancy and morphology of the seeds of herbaceous ornamental plants. Seed Science and Technology, 8, 523-573.

2. Cen, E.-Z. and Van, V.-C. (1965). [Trials on the propagation and cultivation of Lavandula vera.] Sborn. Statej. Introd. Akklim. Rast., Peking, 71-85. (From Horticultural Abstracts, 1967, 37, 7611.)

3. Chavagnat, A. (1978). Etude de la germination des semences de Lavandula angustifolia au laboratoire. Seed Science and Technology, 6, 775-784.

4. Chavagnat, A. (1978). Lavender seed dormancy and germination. Acta Horticulturae, 83, 147-154.

5. Laza, A. and Raianu, M. (1965). [A study on the germination of Lavandula angustifolia seed.] An. Inst. Cerc. Cereale Plante tehn., Fundulea, Ser. C, 33, 379-385. (From Horticultural Abstracts, 1968, 38, 6315.)

6. Menghini, A. and Venanzi, G. (1978). [The effect of growth regulators on the germination of seeds of various medicinal plants.] Annali della Facolta di Agraria, Perugia, 32, 771-783. (From Horticultural Abstracts, 1980, 50, 4582.)

7. Renard, H.A. and Clerc, P. (1978). Leveé de dormance par les gibberellines chez quatre espéces: Impatiens balsamina, Lavandula angustifolia, Brassica rapa et Viola odorata. Seed Science and Technology, 6, 661-677.

8. Ruminska, A., Suchorska, K. and Weglarz, Z. (1978). Effect of gibberellic acid on seed germination of some vegetable and medicinal plants. Acta Horticulturae, 73, 131-136. (From Horticultural Abstracts, 1979 49, 1458.)

MENTHA

M. aquatica L.

M. arvensis L.

mint

M. piperita L.

peppermint

I. Evidence of dormancy

Mint shows orthodox seed storage behaviour (3). Dormancy has been reported in freshly harvested seeds of M. aquatica and M. arvensis (2-4).

II. Germination regimes for non-dormant seeds

M. piperita

TP: 20°/30°C (16h/8h): 21d (ISTA)

TP: 20°/30°C (16h/8h): 16d (AOSA)

III. Unsuccessful dormancy-breaking treatments

M. aquatica, M. arvensis

Light: dark (2)

IV. Partly-successful dormancy-breaking treatments

M. aquatica

Light: light, diffuse light (2)

M. arvensis

Alternating temperatures: (2,3,4)

Pre-chill: (3); 2°C (4); 5°C (2)

Light: light, diffuse light (2); 1.846x10^-3 W cm^-2 (4)

V. Successful dormancy-breaking treatments

M. piperita

Pre-chill, Potassium nitrate (ISTA)

Light (AOSA)

Mentha spp.

Alternating temperatures: 15°/25°C (16h/8h), light, 28d (1)

VI. Comment

Alternating temperatures and light are required for the germination of seeds of Mentha spp. (1-4): an amplitude of 4.5°C has been reported to be partly-successful in breaking dormancy (4). It is suggested that the seeds of all Mentha spp. be tested for germination as recommended by the ISTA for M. piperita, that is on top of moist filter papers in light in an alternating temperature regime of 20°/30°C (16h/8h), with the additional suggestion that pre-chilling be used if the above regime does not promote germination sufficiently.

VII. References

1. Atwater, B.R. (1980). Germination, dormancy and morphology of the seeds of herbaceous ornamental plants. Seed Science and Technology, 8, 523-573.

2. Grime, J.P., Mason, G., Curtis, A.V., Rodman, J., Band, S.R., Mowforth, M.A.G., Neal, A.M. and Shaw, S. (1981). A comparative study of germination characteristics in a local flora. Journal of Ecology, 69, 1017-1059.

3. Ikeda, N., Udo, S., Saisho, I. and Minakata, S. (1960). [Studies on the storage of mint seed.] Science Reports of the Faculty of Agriculture, Okayama, 16, 1-5.

4. Thompson, K., Grime, J.P. and Mason, G. (1977). Seed germination in response to diurnal fluctuations of temperatures. Nature, 267, 147-149.

OCIMUM

O. basilicum L. [O. americanum L.]

sweet basil

O. canum

O. gratissimum

O. kilimandscharicum Guerke

O. tenuiflorum L. [O. sanctum L.]

I. Evidence of dormancy

Seeds of Ocimum spp. exhibit dormancy when tested for germination in the dark with germination being promoted by light (1,5,6). Secondary dormancy can be induced by prolonged, 10 to 20 days, dark imbibition treatments at 26°C (1,5).

II. Germination regimes for non-dormant seeds

O. basilicum

TP: 20°/30°C (16h/8h): 14d (ISTA)

BP: 20°/30°C (16h/8h): 14d (AOSA)

III. Unsuccessful dormancy-breaking treatments

O. basilicum

Light: dark, at 25°C (5); dark, at 28°C, intact or scarified seeds (6); far red, 5 min (5); dark, 25°C, 10d, then light, 25°C (5); white, 35 W m^-2, 10 min-5h/d, after 48h dark, at 28°C (6)

O. tenuiflorum

Light: dark, at 14°-38°C (1); dark, at 22°C (2); red, 10 min, at 14°C (1); blue, 5h, at 26°C (1); dark, 26°C, 20,25d, then red, 10 min, germinate at 26°C (1)

GA₃: co-applied, 10^-4 M, at 14°C, in light, red, 10 min, or dark (1); co-applied, 25, 50 ppm, at 22°C in light, 12h/d (2)

Kinetin: co-applied, 50, 100 ppm, at 22°C in light, 12h/d (2)

Ethrel: co-applied, 100, 200 ppm, at 22°C in light, 12h/d (2)

Boric acid: co-applied, 50, 75 ppm, at 22°C in light, 12h/d (2)

Ascorbic acid: co-applied, 25, 50 ppm, at 22°C in light, 12h/d (2)

Potassium nitrate: co-applied, 25, 50 ppm, at 22°C in light, 12h/d (2)

Storage: hermetic, dry, at -11°C, 8°C, 30°C, or 37°C, 7-30d (2)

IV. Partly-successful dormancy-breaking treatments

O. basilicum

Alternating temperatures: 15°/10°C, 18°/13°C, 21°/16°C, 33°/28°C, 36°/31°C (8h/16h) (7)

Warm stratification: 15°C, 1d, germinate at 25°C, dark (5)

Light: white, 10s-5 min, after 10h dark imbibition, germinate at 25°C in dark (5); white, 5 min, after 1-5d dark imbibition (5); red, 5 min, after 10h dark imbibition (5); white, 35 W m^-2, 5,8,24h/d, at 28°C (6); far red, 5.5 W m^-2, 6-11h/d, at 28°C (6)

Removal of seed covering structures: testa (5)

Scarification: sand paper, germinate at 28°C in light, 5, 13h/d (6)

O. tenuiflorum

Constant temperatures: 26°C, 32°C, light (1)

Warm stratification: 14°C, dark, 4d, germinate at 26°C, red light, 10 min (1); 14°C, dark, 12h, then red light, 10 min, then dark, 4d, germinate at 26°C in dark (1); 38°C, dark, 4d, germinate at 26°C, red light, 10 min (1); 38°C, dark, 12h, then red light, 10 min, then dark, 4d, germinate at 26°C in dark (1); 26°C, dark, 5-15d, germinate at 26°C, light, red, 10 min (1)

Light: white, 10 min (1); white, 5h (1); white, 12h/d (2); white, continuous (2); red, 10 min (1); red, 5h (1); far red, 10 min (1); far red, 5h (1)

GA₃: co-applied, 10 ppm, at 22°C in light, 12h/d (2); co-applied, 10^-4 M, at 26°C, 38°C, dark or light, red, 10 min (1)

Kinetin: co-applied, 75 ppm, at 22°C in light, 12h/d (2)

Ethrel: co-applied, 50 ppm, at 22°C in light, 12h/d (2)

Boric acid: co-applied, 25 ppm, at 22°C in light, 12h/d (2)

Ascorbic acid: co-applied, 10 ppm, at 22°C in light, 12h/d (2)

Potassium nitrate: co-applied, 10 ppm, at 22°C in light, 12h/d (2)

V. Successful dormancy-breaking treatments

O. basilicum

Potassium nitrate (AOSA, ISTA)

Alternating temperatures: 20°/30°C (16h/8h) in light, continuous (3,4); 30°/25°C, 27°/22°C, 24°/19°C (8h/16h), dark (7)

Potassium nitrate: co-applied, 0.2%, at 20°/30°C (16h/8h) (3)

O. canum, O. gratissimum, O. kilimandscharicum, O. tenuiflorum

Alternating temperatures: 20°/30°C (16h/8h) in light (4)

VI. Comment

Light (1,2,3,6) and alternating temperatures (3,4,7) are reported to be required for the promotion of germination of dormant seeds of Ocimum spp. since seeds of O. basilicum and O. tenuiflorum tested at constant temperatures between 14° and 38°C in the dark failed to germinate (1,2,5). Alternating temperatures of 20°/30°C (16h/8h) (3,4) or 22°/27°C (16h/8h) (7) are reported to be promotory. During 14 day germination tests seeds of O. basilicum tested in the dark at 20°/35°C (16h/8h) or 20°C gave 74 and 54% normal germination, whereas those subjected to 8 hours light per day gave 76 and 32% respectively (A). Clearly alternating temperatures are required, but it does appear that light may not be as essential as has been reported provided a suitable alternating temperature regime is used. It is suggested that seeds of Ocimum spp. be tested for germination in an alternating temperature regime of 20°/35°C (16h/8h) with light applied during the period spent at the upper temperature of each cycle.

VII. References

1. Amritphale, D. and Mall, L.P. (1981). Germination of the photoblastic seeds of Ocimum. Plant Science Letters, 20, 263-271.

2. Dey, B.B. and Choudhuri, M.A. (1982). Seed germination as affected by plant age, growth and development stages of Ocimum sanctum. Seed Science and Technology, 10, 243-255.

3. Heit, C.E. (1948). Laboratory germination results with herb and drug seed. Proceedings of the Association of Official Seed Analysts, 38, 58-62.

4. Korsakova, O.M. (1970). [Determination of seed germination in basil.] Sbornik Trudov Aspirantov i Molodykh Nauchnykh Sotrudnikov, Leningrad, 17, 347-353. (From Horticultural Abstracts, 1972, 42, 4529.)

5. Varshney, C.K. (1968). Germination of the light-sensitive seeds of Ocimum americanum Linn. New Phytologist, 67, 125-129.

6. Amritphale, D., Mukhiya, Y.K., Gupta, J.C. and Iyengar, S. (1984). Effect of storage, photoperiod and mechanical scarification on seed germination in Ocimum americanum. Physiologia Plantarum, 61, 649-652.

7. Putievsky, E. (1983). Temperature and daylength influences on the growth and germination of sweet basil and oregano. Journal of Horticultural Science, 58, 583-587.

ORIGANUM

O. majorana L. [Majorana hortensis Moench]

sweet marjoram, annual marjoram

O. sativum

O. vulgare L.

wild marjoram

I. Evidence of dormancy

There is indirect evidence that seeds of O. majorana and O. vulgare may exhibit dormancy (3,4).

II. Germination regimes for non-dormant seeds

O. majorana

TP: 20°C; 20°/30°C (16h/8h): 21d (ISTA)

BP: 15°C: 21d (AOSA)

O. sativum

TP: 20°C; 20°/30°C (16h/8h): 21d (ISTA)

III. Unsuccessful dormancy-breaking treatments

O. majorana

Potassium nitrate: co-applied, 0.2% (1)

O. vulgare

Alternating temperatures: 36°/31°C (8h/16h) (5)

Light: light or dark (3)

IV. Partly-successful dormancy-breaking treatments

O. majorana

Alternating temperatures: 10°/20°C, 20°/30°C (16h/8h) (1)

GA₃: pre-applied, 24h, 100-1000 ppm (4)

O. vulgare

Constant temperatures: 6°-10.5°C, 15°-31.5°C (3)

Alternating temperatures: 24°/19°C, 21°/16°C, 27°/22°C, 18°/13°C, 15°/10°C, 30°/25°C, 33°/28°C (8h/16h) (5)

V. Successful dormancy-breaking treatments

O. majorana

Constant temperatures: 15°C (1)

Fusicoccin: pre-applied, 24h, 5 ppm (4)

O. vulgare

Constant temperatures: 15°C (2); 12°-13.5°C (3)

VI. Comment

In a comparison of the germination of seeds of O. vulgare in seven different alternating temperature environments the regime 24°/19°C (8h/16h) was superior, but failed to promote full germination (5): in other investigations with seeds of O. vulgare constant temperatures of 15°C (2) and 12°-13.5°C (3) promoted full germination. Similarly, although an alternating temperature regime of 10°/20°C (16h/8h) was recommended in previous ISTA rules as a dormancy-breaking treatment for seeds of O. majorana a constant temperature of 15°C (also recommended previously by ISTA) is reported to be more promotory than this alternating temperature regime (1). Consequently it is suggested that seeds of Origanum spp. be tested at a constant temperature of 15°C (1,2,AOSA) with, if necessary, an extended test duration.

VII. References

1. Cseresnyes, Z. and Baleanu, M. (1978). [Improving the methods for germinating seed of Hypericum perforatum, Atropa belladonna, Majorana hortensis, Salvia Sclarea and Solanum laciniatum.] Analele Institutului de Cercetari pentru Cereale si plante Tehnice-Fundulea, 43, 111-116. (From Seed Abstracts, 1980, 3, 2371.)

2. Heit, C.E. (1948). Laboratory germination results with herb and drug seed. Proceedings of the Association of Official Seed Analysts, 38, 58-62.

3. Macchia, M., Benvenuti, A. and Angelini, L. (1983). [Germination characteristics of a series of medicinal species.] Revista della Ortoflorofrutticoltura Italiana, 67, 165-190.

4. Menghini, A. and Venanzi, G. (1977/1978). [The effect of growth regulators on the germination of seeds of various medicinal plants.] Annali della Facolta di Agraria, Perugia, 32, 771-783. (From Seed Abstracts, 1980, 3, 2391.)

5. Putievsky, E. (1983). Temperature and daylength influences on the growth and germination of sweet basil and oregano. Journal of Horticultural Science, 58, 583-587.

SALVIA

S. coccinea Juss. [S. rosea Vahl.]

S. farinacea Benth.

mealycup sage

S. glutinosa L.

S. officinalis L.

sage

S. patens Cav.

S. pratensis L.

S. reflexa Hornem

mintweed

S. Sclarea L. clary

S. sonomensis

S. splendens Sello [S. colorans Hort.]

scarlet sage

S. viridis

I. Evidence of dormancy

Seeds of Salvia spp. can show considerable dormancy (4-6). Seeds of S. sclarea require 6 months after-ripening to remove dormancy (6).

II. Germination regimes for non-dormant seeds

S. coccinea