CHAPTER 30. COMPOSITAE

The Compositae comprise about 20000 species of herbaceous plants in more than 800 genera which provide oils (e.g. Guizotia abyssinica (L. f.) Cass., niger), leaf vegetables (e.g. Lactuca sativa L., lettuce), edible tubers (e.g. Helianthus tuberosus L., Jerusalem artichoke) and other products (e.g. Chrysanthemum cinerariaefolium (Trev.) Bocc., pyrethrum). The seeds are achenes (see Chapter 3, Volume I) and show orthodox storage behaviour.

SEED DORMANCY AND GERMINATION

In most genera the seeds normally exhibit dormancy, but the problem this poses when attempting to promote seed germination varies considerably between both species and accessions. Light, pre-chill, potassium nitrate and temperatures around 15°C tend to promote germination. The seeds are non-endospermic and B.R. Atwater classifies the Compositae as a unique morphological category, viz: axile foliar embryos with fibrous seed coat and spearate inner semi-permeable membranous layer (see Table 17.2, Chapter 17).

Detailed information on seed dormancy and germination is provided in this chapter for the genera Carthamus, Cichorium, Guizotia, Helianthus, Lactuca and Parthenium. In addition, Table 30.1 provides a summary of germination test procedures and dormancy-breaking treatments for very many other species and the algorithm below may be helpful in developing germination test procedures for species where no advice is provided here and for difficult accessions where the regimes summarised in Table 30.1 are unable to promote full germination.

RBG Kew Wakehurst Place algorithm

The first step in the algorithm is to test three samples of seeds at constant temperatures of 11°C, 16°C and 26°C with light applied for 12h/d.

If none of these regimes is successful in promoting full germination then the second step of this algorithm is to test a further sample of seeds at a constant temperature of 6°C with light applied for 12h/d if the greatest germination occurred at 11°C in step one, or to test a further sample of seeds at a constant temperature of 21°C with light applied for 12h/d if the greatest germination occurred at 16°C or 26°C in step one. If there was little difference in germination between tests at the three constant temperatures (step one) then test two further samples of seeds at 6°C and 21°C with light applied for 12h/d.

If any of the regimes applied in the second step does not promote full germination then the third step of the algorithm is to test a further sample of seeds at an alternating temperature of 23°/9°C (12h/12h) with light applied for 12h/d during the period spent at the upper temperature of each cycle if the second step was to test at 6°C or, where two regimes were used in step two, the greatest germination was observed at 6°C. Otherwise take two further samples of seeds and test in 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 of each cycle.

If any of the regimes applied in the third step of the algorithm does not promote full germination then the fourth step of the algorithm is to pre-chill a further sample of seeds at 2° to 6°C for 8w: the subsequent germination test regime is that judged most suitable from a comparison of the results of the previous steps of the algorithm.

If the additional treatment of pre-chilling does not result in full germination then the fifth step of the algorithm is to take a further three samples of seeds, chip the fibrous seed coats and test in the most promotory regime determined in the previous steps (this may include a pre-chill treatment if the fourth step resulted in an increase in germination over previous steps) with GA₃ co-applied in the germination test substrates at three concentrations, viz: 3 x 10^-4 M, 7 x 10^-4 M, and 2.6 x 10^-3 M. Some experimentation with these conditions may be helpful. For example, if a trend in the results at different GA₃ concentrations is apparent it may be worthwhile investigating the response of germination to a more extreme concentration; or chipping plus pre-chill may be sufficient to promote germination without a GA₃ treatment.

If full germination has not been promoted, the sixth 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 regimes 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 environment can be obtained from the information provided for six genera in this chapter, from Table 17.2 (Chapter 17) and the long list of dormancy-breaking treatments in Table 30.1.

TABLE 30.1 Summary of germination test recommendations for species within the Compositae

Species and Authority	Substrate	Temperature	Duration	Additional directions	Source
Achillea clavennae L.	TP; BP	20°/30°C; 20°C	14d	light	ISTA
Achillea filipendulina Lam.	TP; BP	20°/30°C; 20°C	14d	light	ISTA
Achillea millefolium L.	TP	20°/30°C	14d		ISTA
	TP	20°/30°C			M&O
Achillea ptarmica L.	TP; BP	20°/30°C; 20°C	14d	light	ISTA
	TP	20°/30°C	10d	light, check for empty seeds	AOSA
		20°/30°C	14d		Atwater
Ageratum houstonianum Mill.	TP	20°/30°C; 20°C	14d		ISTA
	TP	20°/30°C	7d		AOSA
		20°/30°C	10d		Atwater
Agoseris grandiflora	TP	15°C; 20°C			M&O
Amberboa moschata (L.) DC.	TP; BP	20°/30°C; 15°C; 20°C	21d	light, pre-chill	ISTA
	TP	15°C	21d		AOSA
Ambrosia artemsifolia	TP	20°/30°C		light	M&O
Ammobium alatum R. Br.	TP; BP	20°/30°C; 20°C	14d		ISTA
Anthemis tinctoria L. Kelwayi	TP	15°C	14d	light, avoid temperatures above 15°C	AOSA
Anthemis sancti-johannis Turrill	TP	15°C	14d	light, avoid temperatures above 15°C	AOSA
Arctium lappa L.	BP	20°/30°C	14d		AOSA
Arctium minus Schk.	TP	23°/30°C	28d		R&S
Arctotis stoechadifolia Bergius	TP; BP	20°/30°C; 15°C; 20°C	21d	light	ISTA
Var grandis (Thunb.) Less	TP	15°C	18d	check for empty seeds	AOSA
		15°C	21d		Atwater
Artemisia absinthium L.	TP	20°/30°C	21d		ISTA
	TP	20°/30°C	14d		Heit
Artemisia dracunculus L.	TP	20°/30°C	21d		ISTA
Artemisia maritima L.	TP	20°/30°C	21d		ISTA
Artemisia vulgaris L.	TP	20°/30°C	21d		ISTA
		20°C	14d		Atwater
Aster alpinus L.	TP	20°/30°C; 20°C	14d	pre-chill	ISTA
Aster amellus L.	TP	20°/30°C; 20°C	14d	pre-chill	ISTA
Aster canescens	TP	15°C		light	M&O
Aster dumosus L.	TP	20°/30°C; 20°C	14d	pre-chill	ISTA
Aster glaucoides (Nutt.) Elliot		20°C	5d	excise embryos	Atwater
Aster spp.	TP	20°/30°C		light	M&O
Baccharis spp.		20°C	10d		Atwater
Baileya multiradiata Torr.	TP	20°/30°C	14d	light, if seeds infected then treat	AOSA
Balsamorhiza sagittata (Pursh.) Nutt.		20°C	5d	excise embryos	Atwater
Bellis perennis L.	TP	20°/30°C; 20°C	14d	pre-chill	ISTA
	TP	20°/30°C	6d	light	AOSA
		20°C	14d		Atwater
Brachycome iberidifolia Benth.	TP	20°/30°C; 15°C	14d		ISTA
	TP	15°C	12d	avoid temperatures above 15°C	AOSA
Buphthalmum salicifolium L.	TP	20°/30°C	14d	light	AOSA
Calendula officinalis L.	TP; BP	20°/30°C; 20°C	14d	light, pre-chill, potassium nitrate	ISTA
	TP	20°C	10d	potassium nitrate, test at 15°C	AOSA
		15°C	14d	light, potassium nitrate, 0.2%	Atwater
Callistephus chinensis (L.) Nees	TP	20°/30°C; 20°C	14d	light	ISTA
	TP	20°C	8d	fungicide treatment may be necessary	AOSA
		20°C	14d		Atwater
Castalis tragus (Ait.) Norl.	TP; BP	20°/30°C; 15°C; 20°C	14d	light, pre-chill, potassium nitrate	ISTA
Centaurea americana Nutt.	TP; BP	20°/30°C; 15°C; 20°C	21d	light, pre-chill, pre-soak, 24h	ISTA
	BP	20°/30°C	14d	clip radicle end of seed, extend test for 5d	AOSA
		20°/30°C	28d		Atwater
Centaurea cineraria L.	TP	15°C	21d		AOSA
		15°C	21d		Atwater
Centaurea cyanus L.	TP; BP	20°/30°C; 15°C; 20°C	21d	light, pre-chill	ISTA
	TP	15°C	8d	fungicide treatment may be necessary	AOSA
		15°C	14d		Atwater
Centaurea dealbata Willd.	TP; BP	20°/30°C; 15°C; 20°C	21d	light, pre-chill	ISTA
Centaurea diffusa	TP	20°/30°C			M&O
Centaurea gymnocarpa Moris & DeNot.	TP; BP	20°/30°C; 15°C; 20°C	21d	light, pre-chill	ISTA
	TP	15°C	16d		AOSA
		15°C	21d		Atwater
Centaurea imperialis Bornm.	TP; BP	20°/30°C; 15°C; 20°C	21d	light, pre-chill	ISTA
	TP	15°C	16d		AOSA
		15°C	21d		Atwater
Centaurea macrocephala Puschk. ex Willd.	TP; BP	20°/30°C; 15°C; 20°C	21d	light, pre-chill	ISTA
Centaurea montana L.	TP; BP	20°/30°C; 15°C; 20°C	21d	light, pre-chill	ISTA
Centaurea ragusina L.	TP; BP	20°/30°C; 15°C; 20°C	21d	light, pre-chill	ISTA
Centaurea solstitialis	TP	20°/30°C; 15°C; 20°C		light	M&O
Chrysanthemum carinatum Schousb.	TP; BP	20°/30°C; 15°C	21d	light, pre-chill	ISTA
	TP	15°C	10d	check for empty seeds	AOSA
Chrysanthemum coronarium L.	TP; BP	20°/30°C; 15°C	21d	light, pre-chill	ISTA
	TP	15°C	10d	check for empty seeds	AOSA
Chrysanthemum multicaule Desf.	TP; BP	20°/30°C; 20°C	21d	light, pre-chill	ISTA
Chrysanthemum nivellei Br.-Blanq. & Maire	TP; BP	20°/30°C; 20°C	21d	pre-chill	ISTA
Chrysanthemum ptarmiciflorum (Webb) Brenan	TP	15°C	12d	light, fungicide treatment may be necessary	AOSA
Chrysanthemum segetum L.	TP; BP	20°/30°C; 15°C	21d	pre-chill	ISTA
	TP	15°C	10d	check for empty seeds	AOSA
Chrysanthemum spp.		20°C	14d		Atwater
Chrysopsis spp.		20°C	5d	excise embryos	Atwater
Chrysothamnus nauseosus (Pall.) Britt.		20°C	14d		Atwater
Cirsium vulgare	TP	20°/30°C			M&O
Cnicus benedictus L.	TP; BP; S	20°/30°C	21d	pre-chill	ISTA
Coreopsis basalis (Otto & A. Dietr.) Blake	TP	20°C	8d		AOSA
Coreopsis cardaminifolia (DC.) Nutt.	TP; BP	20°/30°C; 20°C	14d	light, pre-chill, potassium nitrate	ISTA
Coreopsis coronata L.	TP; BP	20°/30°C; 20°C	14d	light, pre-chill, potassium nitrate	ISTA
Coreopsis drummondii Torr. & Gray	TP; BP	20°/30°C; 20°C	14d	light, pre-chill, potassium nitrate	ISTA
Coreopsis lanceolata L.	TP; BP	20°/30°C; 20°C	14d	light, pre-chill, potassium nitrate	ISTA
	TP	20°/30°C; 15°C	21d	light, potassium nitrate	AOSA
		20°/30°C; 15°C; 20°C	40d	potassium nitrate, 0.2%	Atwater
Coreopsis maritima (Nutt.) Hook. f.	TP; BP	20°/30°C; 20°C	14d	light, pre-chill, potassium nitrate	ISTA
Coreopsis tinctoria Nutt.	TP	20°/30°C; 20°C	14d	pre-chill, potassium nitrate	ISTA
	TP	20°C	8d		AOSA
Cosmos bipinnatus Cav.	TP; BP	20°/30°C; 20°C	14d	light, pre-chill, potassium nitrate	ISTA
	TP	20°/30°C	8d	light, potassium nitrate, extend test period	AOSA
		20°/30°C	14d	test at 15°C	Atwater
Cosmos sulphureus Cav.	TP; BP	20°/30°C; 20°C	14d	light, pre-chill, potassium nitrate	ISTA
	TP	20°/30°C	8d	light, potassium nitrate	AOSA
		20°/30°C	14d	test at 15°C	Atwater
Crepis capillaris	TP	20°/30°C; 15°C		light	M&O
Cynara cardunculus L.	BP; S	20°/30°C	21d		ISTA
	BP	20°/30°C	21d		AOSA
Cynara scolymus L.	BP; S	20°/30°C	21d		ISTA
	BP	20°/30°C	21d		AOSA
	TP	20°/30°C	21d		Fornerod
Dahlia pinnata Cav.	TP; BP	20°/30°C; 15°C; 20°C	21d	pre-chill	ISTA
		15°C	14d		Atwater
Dahlia spp.	TP; BP	15°C	14d	seeds sensitive to drying out in test	AOSA
Dendrathema indicum (L.) Desm.	TP; BP	20°/30°C; 20°C	21d	light, pre-chill	ISTA
Dimorphotheca pluvialis (L.) Moench	TP; BP	20°/30°C; 15°C	14d	light, pre-chill, potassium nitrate	ISTA
Dimorphotheca sinuata DC.	TP	15°C	10d	light, potassium nitrate, check for empty seeds	AOSA
		15°C	14d		Atwater
Doronicum orientale Hoffm.	TP	20°/30°C; 20°C	21d	potassium nitrate, pre-chill	ISTA
	TP	20°C	21d	light	AOSA
Echinacea purpurea (L.) Moench	TP; BP	20°/30°C; 20°C	21d	light, pre-chill	ISTA
	TP	20°/30°C	12d	light	AOSA
Echinops ritro L.	TP; BP	20°/30°C	21d		ISTA
	TP	20°/30°C	21d	light, good moisture supply	AOSA
Encelia californica Nutt.		20°C	5d	excise embryos	Atwater
Encelia farinosa Gray		20°C	5d	excise embryos	Atwater
Erigeron speciosus (Lindl.) DC.	TP	20°/30°C; 20°C	28d		ISTA
	TP	15°C	16d	light	AOSA
Eriophyllum confertiflorum (DC.) Gray		20°C	5d	excise embryos	Atwater
Eriophyllum lanatum Forbes	TP	20°/30°C			M&O
Gaillardia aristata Pursh.	TP; BP	20°/30°C; 20°C	21d	light, pre-chill	ISTA
	TP	20°/30°C	10d	light, check for empty seeds	AOSA
	TP	20°/30°C		light	M&O
		20°/30°C	14d		Atwater
Gaillardia pulchella Foug.	TP; BP	20°/30°C; 20°C	21d	light, pre-chill	ISTA
	TP	20°/30°C	10d	light, check for empty seeds	AOSA
		20°/30°C	14d		Atwater
Gazania rigens (L.) Gaertn.	TP; BP	20°/30°C; 15°C	21d	pre-chill	ISTA
	TP	15°C	12d	check for empty seeds	AOSA
		15°C	21d		Atwater
Gerbera jamesonii Hook. f.	TP	20°/30°C; 20°C	14d		ISTA
	TP; BP	20°/30°C; 20°C	10d	light	AOSA
		20°/30°C	14d		Atwater
Gnaphalium microcephalum	TP	15°C		light	M&O
Grindelia stricta DC.		20°C	14d	excise embryos	Atwater
Helenium autumnale L.	TP; BP	20°/30°C; 20°C	14d		ISTA
Helenium spp.	TP	20°/30°C	16d	light, check for empty seeds	AOSA
Helichrysum bracteatum (Vent.) Andr.	TP; BP	20°/30°C; 15°C	14d	light, potassium nitrate, pre-chill	ISTA
	TP	15°C	10d	light, potassium nitrate	AOSA
Heliopsis helianthoides (L.) Sweet	TP; BP	20°/30°C	21d	potassium nitrate, pre-soak, 24h	ISTA
Heliopsis spp.	TP	20°/30°C	18d		AOSA
Helipterum craspedioides				excise embryos	Atwater
Helipterum humboldtianum (Gaudich.) DC.	TP; BP	20°/30°C; 15°C	21d	pre-chill	ISTA
Helipterum manglesii (Lindl.) F. Muell.	TP; BP	20°/30°C; 15°C	21d	pre-chill	ISTA
Helipterum roseum (Hook.) Benth.	TP; BP	20°/30°C; 15°C	21d	pre-chill	ISTA
	TP	15°C	18d		AOSA
		20°C	14d		Atwater
Hymenoclea salsola T. & G.		20°C	5d	excise embryos	Atwater
Hypochaeris radicata	TP	20°/30°C			M&O
Inula grandiflora Willd.	TP	20°/30°C	14d	light	AOSA
Inula helenium L.	TP	20°/30°C; 20°C	28d		ISTA
Lapsana communis	TP	20°/30°C			M&O
Layia platyglossa (F. & M.) Gray	TP	15°C	8d	light, avoid temperatures above 15°C	AOSA
		20°C	14d		Atwater
Leontodon nudicaulis		20°/30°C			M&O
Leontopodium alpinum Cass.	TP	20°/30°C; 20°C	14d	pre-chill	ISTA
Leucanthemum maximum Ram. DC.	TP; BP	20°/30°C; 20°C	21d	light, pre-chill	ISTA
Leucanthemum vulgare Lam.	TP; BP	20°/30°C; 20°C	21d	light, pre-chill	ISTA
Liatris pycnostachya Michx.	TP	20°/30°C	28d		ISTA
Liatris spicata (L.) Willd.	TP	20°/30°C	28d		ISTA
Lonas annua (L.) Vines & Druce	TP	20°/30°C	28d		ISTA
Machaeranthera tanacetifolia (HBK) Nees	TP	15°C	10d	avoid temperatures above 18°C	AOSA
Madia exigua	TP	15°C			M&O
Matricaria chamomilla L.	TP	20°/30°C	14d	pre-chill	ISTA
Matricaria maritima	TP	20°/30°C; 20°C	14d	pre-chill	ISTA
Matricaria perforata Merat	TP	20°/30°C; 20°C	14d	pre-chill	ISTA
Matricaria recutila L.	TP	20°/30°C; 20°C	14d	pre-chill	ISTA
Matricaria spp.	TP	20°/30°C; 20°C	7d	light	AOSA
		20°C	14d		Atwater
Osteospermum ecklonis (DC.) Norl.	TP; BP	20°/30°C; 15°C	14d	light, pre-chill, potassium nitrate	ISTA
Pyrethrum spp.	TP	15°C	21d	potassium nitrate	AOSA
Rudbeckia fulgida Ait.	TP; BP	20°/30°C; 20°C	21d	light, pre-chill	ISTA
Rudbeckia hirta L.	TP; BP	20°/30°C; 20°C	21d	light, pre-chill	ISTA
Rudbeckia spp.		20°/30°C	14d		Atwater
Sanvitalia procumbens Lam.	TP; BP	20°/30°C; 20°C	14d	pre-chill	ISTA
	TP; BP	20°/30°C; 20°C	7d	light, check for empty seeds	AOSA
Scorzonera hispanica L.	TP; BP	20°/30°C; 20°C	8d	pre-chill	ISTA
	BP	20°/30°C	8d	pre-chill, 10°C, 5d	Fornerod
Senecio bicolor (Willd.) Tod.	TP	20°/30°C; 20°C	21d	pre-chill	ISTA
Senecio cruentus (L'Her.) DC.	TP	20°/30°C; 20°C	21d	pre-chill	ISTA
	TP	20°C	14d	light	AOSA
		20°C	14d		Atwater
Senecio elegans L.	TP	20°/30°C; 20°C	21d	pre-chill	ISTA
Senecio jacobea	TP	15°C		light	M&O
Sonchus arvensis	TP	20°/30°C		light	M&O
Silybum marianum (L.) Gaertn.	TP; BP; S	20°/30°C; 20°C	21d	pre-chill	ISTA
Tagetes erecta L.	TP; BP	20°/30°C; 20°C	14d	light	ISTA
Tagetes patula L.	TP; BP	20°/30°C; 20°C	14d	light	ISTA
Tagetes tennifolia Cav.	TP; BP	20°/30°C; 20°C	14d	light	ISTA
Tagetes spp.	TP	20°/30°C; 20°C	7d	light, check for broken seedlings	AOSA
		20°/30°C	10d		Atwater
Tanacetum achilleifolium (Bieb.) Sch. Bip.	TP; BP	20°/30°C; 15°C	21d	light, pre-chill	ISTA
Tanacetum cineraiifolium (Trev.) Sch. Bip.	TP; BP	20°/30°C; 20°C	21d	pre-chill	ISTA
Tanacetum coccineum (Willd.) Grierson	TP; BP	20°/30°C; 15°C	21d	light, pre-chill, potassium nitrate	ISTA
Tanacetum parthenium (L.) Sch. Bip.	TP; BP	20°/30°C; 20°C	21d	light, pre-chill	ISTA
Tanacetum vulgare L.	TP	20°/30°C			M&O
Taraxacum erythrospermum	TP	20°/30°C; 15°C; 20°C		light, test at 15°C	M&O
Taraxacum officinale Wigg.	TP	20°/30°C; 20°C	21d		ISTA
	TP	20°/30°C	21d	light	AOSA
	TP	20°/30°C; 15°C		light	M&O
	TP	20°C	14d	light	Heit
Tithonia rotundifolia (Mill.) Blake	TP; BP	20°/30°C	8d	light	AOSA
Tragopogon porrifolius L.	TP; BP	20°C	10d	pre-chill	ISTA
	BP	15°C	10d	pre-chill, 10°C, 3d	AOSA
	TP	20°/30°C		light	M&O
Tragopogon spp.	BP	15°C	10d		Everson
Venidium fastuosum (Jacq.) Stapf	TP	20°/30°C	10d	light	AOSA
Viquiera laciniata Gray		20°C	5d	excise embryos	Atwater
Xeranthemum annuum L.	TP; BP	20°/30°C; 20°C	14d		ISTA
Zinnia acerosa (DC.) Gray	TP; BP	20°/30°C; 20°C	7d	light, check for empty seeds	AOSA
Zinnia angustifolia HBK	TP; BP	20°/30°C; 20°C	7d	light, check for empty seeds	AOSA
Zinnia elegans Jacq.	TP; BP	20°/30°C; 20°C	10d	light, pre-chill	ISTA
	TP; BP	20°/30°C; 20°C	7d	light, check for empty seeds	AOSA
Zinnia grandiflora Nutt.	TP; BP	20°/30°C; 20°C	7d	light, check for empty seeds	AOSA
Zinnia haageana Regel	TP; BP	20°/30°C; 20°C	10d	light, pre-chill	ISTA
Zinnia peruviana L.	TP; BP	20°/30°C; 20°C	7d	light, check for empty seeds	AOSA
Zinnia spp.		20°/30°C	7d		Atwater

CARTHAMUS

C. alexandrius
C. flavescens
C. glaucus
C. lanatus L.	saffron thistle
C. oxyacantha Bieb.	wild safflower
C. palaestinus Eig.
C. tinctorius L.	safflower

I. Evidence of dormancy

Freshly harvested seeds of the cultivated safflower (C. tinctorius L.) are usually non-dormant (4,6,7,9), but seeds of the wild species, C. alexandrius, C. flavescens, C. glaucus, C. lanatus, C. oxyacantha and C. palaestinus may show considerabl e dormancy (1,3,4,6-9). For example, seeds of C. oxyacantha after-ripened for one year at 23°C gave only 33% germination despite being 82% viable (3). Seeds of the inter-specific hybrids between C. tinctorius and the wild species can also be dormant (7,9).

II. Germination regimes for non-dormant seeds

C. tinctorius

TP; BP; S: 25°C; 20°/30°C (16h/8h): 14d (ISTA)

BP; TP; S: 15°C; 20°C: 14d (AOSA)

Constant temperatures: 15°-20°C (4)

Alternating temperatures: 16°/27°C (12h/12h) (9)

III. Unsuccessful dormancy-breaking treatments

C. lanatus

Pre-soak: in dark, germinate at 25°C in dark (8)

Pre-wash: 24h with far red irradiation, 7x10^-6 mol m^-2 s^-1 (8)

C. oxyacantha

Pre-chill: 0°C, 28d, then scarify (4); 4°C, 70d (3); 4°C, 70d, then scarify (3)

IV. Partly-successful dormancy-breaking treatments

C. lanatus

Pre-soak: 2-24h, continuous light, 10^-5 mol m^-2 s^-1 (8); 24h, in dark, germinate at 25°C in light, 10^-5, 25x10^-5 mol m^-2 s^-1 (8); 24h, in light, 10^-5 mol m^-2 s^-1, germinate at 25°C in dark or light, 10^-5, 25x10^-5 mol m^-2 s^-1 (8); 24h, in light, 25x10^-5 mol m^-2 s^-1, germinate at 25°C in dark or light, 10^-5, 25x10^-5 mol m^-2 s^-1 (8)

Pre-wash: 24h, continuous light, 10^-5 mol m^-2 s^-1 (8)

C. oxyacantha

Constant temperatures: 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, optimum at 15°-20°C, in dark (4)

Pre-chill: 0°C, 1m (4); 3°-5°C, 2-8w (3); 3°-5°C, 2-8w, then cut off tip of seed coat (3)

Removal of seed covering structures: cut off tip of seed coat (1,3,4)

Polyethylene glycol: co-applied, -1, -2 bar (2)

Pre-wash: (6)

V. Successful dormancy-breaking treatments

C. lanatus

Pre-soak: 24h, continuous light, 650 nm, 7x10^-6 mol m^-2 s^-1, germinate at 25°C in dark (8)

C. oxyacantha

Pre-soak: 1-4d, germinate at 18°C in dark (6)

C. tinctorius

Light at 15°C (AOSA)

Constant temperatures: 15°C (5)

VI. Comment

Constant temperatures of 15°C and 20°C are suitable for the germination of seeds of C. oxyacantha and C. tinctorius (4,6). Pre-soaking the seeds in water for 24 hours promotes the germination of C. oxyacantha and C. lanatus (6,9), and does not damage seeds of C. tinctorius (6). The effect of light is very significant during both the pre-soak period and the germination test - high light intensity (25x10^-5 mol m^-2 s^-1) being less suitable for germination than a low light intensity (10^-5 mol m^-2 s^-1) (8).

Consequently the following germination test regime is suggested for seeds of all Carthamus spp. - including the cultivated C. tinctorius and its hybrids: pre-soak the seeds in water for 24 hours under red light (650 nm, 7x10^-6 mol m^-2 s^-1) and test for germina tion at 15°C in the dark.

VII. References

1. Bassiri, A. and Kheradnam, M. (1976). Relationships between seed color and viability, germination and seedling growth of wild safflower ecotypes. Canadian Journal of Plant Science, 56, 911-917.

2. Bassiri, A., Khosh-Khui, M. and Rouhani, I. (1977). The influences of simulated moisture stress conditions and osmotic substances on germination and growth of cultivated and wild safflowers. Journal of Agricultural Science (Cambridge), 88, 95-100.

3. Bassiri, A. and Rouhani, I. (1976). Effect of seed treatment on germination of wild safflower. Weed Science, 24, 233-234.

4. Bassiri, A., Rouhani, I. and Ghorashy, S.R. (1975). Effect of temperature and scarification on germination and emergence of wild safflower, Carthamus oxyacantha Bieb. Journal of Agricultural Science (Cambridge), 84, 239-243.

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

6. Kheradnam, M. and Bassiri, A. (1980). Seed germination and seedling growth inhibition caused by safflower seed extracts. Agronomy Journal, 72, 31-35.

7. Kotecha, A. and Zimmerman, L.H. (1978). Genetics and seed dormancy and its association with other traits in safflower. Crop Science, 18, 1003-1007.

8. Wright, G.C., McWilliam, J.R. and Whalley, R.D.B. (1980). Effects of light and leaching on germination of saffron thistle (Carthamus lanatus L.). Australian Journal of Plant Physiology, 7, 587-594.

9. Zimmerman, L.H. (1972). Variation and selection for pre-harvest seed dormancy in safflower. Crop Science, 12, 33-34.

CICHORIUM

C. endivia L.	endive
C. intybus L.	chicory, succory
C. pumilum Jacq.	wild chicory

I. Evidence of dormancy

Freshly harvested seeds of C. endivia can exhibit considerable dormancy (11). Secondary dormancy may be induced if seeds of Cichorium spp. are exposed to high temperatures in the absence of light (6).

II. Germination regimes for non-dorment seeds

C. endivia

TP: 20°C; 20°/30°C (16h/8h): 14d (ISTA)

TP; TS: 20°/30°C (16h/8h): 14d (AOSA)

Constant temperatures: 20°C (11)

Alternating temperatures: 20°/30°C (16h/8h) (11)

C. intybus

TP: 20°C; 20°/30°C (16h/8h): 14d (ISTA)

TP; TS: 20°/30°C (16h/8h): 14d (AOSA)

Alternating temperatures: 20°/30°C (16h/8h) (3)

III. Unsuccessful dormancy-breaking treatments

C. endivia

Constant temperatures: 2°C (1,9); above 30°C, dark (6,9)

Potassium nitrate: co-applied, 0.1, 0.2% (11)

IV. Partly-successful dormancy-breaking treatments

C. endivia

Constant temperatures: 7°C, light, 8h/d (1)

Warm stratification: 18°C, 25°C, 4-24h, germinate at 30°C, with or without thiourea, co-applied, 0.5% (6)

C. intybus

Constant temperatures: 20°C, light (2); 15°-25°C, dark (8); 11°-25°C, light, 30 W m^-2, 8h/d (10)

Alternating temperatures: 20°/30°C (18h/6h) in light (2); 20°/30°/8°C (10h/8h/6h) in light (2)

C. pumilum

Thiourea: co-applied, 0.2%, at 27°C in light (5)

V. Successful dormancy-breaking treatments

C. endivia

Potassium nitrate (ISTA)

Light, Potassium nitrate, test in soil, excess moisture for first 24h (AOSA)

Constant temperatures: 17°C, light, 30 W m^-2, 8h/d (1); 13°-21°C, light, 30 W m^-2, 8h/d (9)

Thiourea: co-applied, 0.5% (11)

C. intybus

Potassium nitrate (ISTA)

Light, Potassium nitrate, test in soil (AOSA)

Constant temperatures: 10°-20°C, dark (7)

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

VI. Comment

Although thiourea, co-applied at 0.5%, promoted the germination of dormant seeds of C. endivia (11), abnormal germination occurred (11): treatment at a lower concentration might be worth investigating. Seeds of Cichorium spp. require light (1,2,4,5,9-11) and a relatively low temperature - 10° to 25°C - (1,7-11) for germination. The seed lots used in most of the cited papers showed little dormancy. For such seed lots the ISTA/AOSA germination test procedures are satisfactory. We suggest, however, that gene banks handling more dormant accessions of Cichorium spp. should test the seeds at 15°C in light.

The amount of moisture held by the germination test substratum can be critical: excess moisture, either from the use of many layers of wetted paper or thoroughly wetted absorbent cotton, can greatly promote the germination of dormant seeds of C. endivia (11). It has been suggested that light is only promotory when applied to tests carried out in the presence of excess moisture (11). Hence the AOSA recommendations. We suggest, therefore, that where possible germination tests are carried out on thoroughly wetted absorbent cotton.

VII. References

1. Bierhuizen, J.F. and Wagenvoort, W.A. (1974). Some aspects of seed germination in vegetables. 1. The determination and application of heat sums and minimum temperature for germination. Scientia Horticulturae, 2, 213-219.

2. Cross, H. (1931). Laboratory germination of weed seeds. Proceedings of the Association of Official Seed Analysts, 24, 125-128.

3. Fornerod, C. (1975). Remarques sur la germination des semences potagères en laboratoires. Revue Horticole Suisse, 48, 6-9.

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

5. Moursi, M.A., Rizk, T.Y. and El-Deepah, H.R. (1977). Weed seed germination responses to some chemical treatments. Egyptian Journal of Agronomy, 2, 197-209.

6. Thompson, R.C. (1946). Germination of endive seed (Cichorium endivia) at high temperature stimulated by thiourea and by water treatments. Proceedings of the American Society for Horticultural Science, 47, 323-326.

7. Valette, R. (1978). Influence de la température sur la germination des semences de chicoreé de Bruxelles. Bulletin des Recherches Agronomiques de Gembloux, 13, 183-196.

8. Valette, R. (1981). Etude de la germination à differentes temperatures de semences de Chicoreé de Bruxelles. Revue de l'Agriculture, 34, 995-1007.

9. Wagenvoort, W.A. and Bierhuizen, J.F. (1977). Some aspects of seed germination in vegetables. II. The effect of temperature fluctuation, depth of sowing, seed size and cultivar, on heat sum and minimum temperature for germination. Scientia Horticulturae, 6, 259-270.

10. Wagenvoort, W.A., Boot, A. and Bierhuizen, J.F. (1981). Optimum temperature range for germination of vegetable seeds. Gartenbauwissenschaft, 46, 97-101.

11. Munn, M.T. (1949). Endive seed germination. Proceedings of the Association of Official Seed Analysts, 39, 122-125.

GUIZOTIA

G. abyssinica (L. f.) Cass.

niger, noog

I. Evidence of dormancy

There is little literature on niger seed germination in the literature and little evidence of dormancy.

II. Germination regimes for non-dormant seeds

Constant temperatures: 15°C, 17°C, 20°C in light (1)

III. Unsuccessful dormancy-breaking treatments

-

IV. Partly-successful dormancy-breaking treatments

Pre-chill: 10°C, 2-14h, then germinate at 27°-30°C, 52h (2) Warm stratification: 35°C, 2-12h, then germinate at 27°-30°C, 52h (2)

Diethyl sulphate: pre-applied, 12h, 3x10^-2 M (3)

V. Successful dormancy-breaking treatments

-

VI. Comment

Non-dormant seeds of G. abyssinica germinate readily at both 20°C and 20°/30°C (16h/8h) (A). It is suggested that the seeds be tested on top of filter paper in an alternating temperature regime of 20°/30°C (16h/8h) for 14 days. Dormant seeds may benefit from a warm stratification or pre-chill treatment prior to testing in this regime (2).

VII. References

1. Mesfin, A. (1977). Ecophysiology of noog (Guizotia abyssinica Cass.). Dissertation Abstracts International, B, 38, 990-991.

2. Pasha, M.K. and Salehuzzaman, M. (1978). Effect of low and high temperatures on the germination of rape seed and niger seed. Indian Journal of Agricultural Science, 48, 284-286.

3. Rao, P.K. and Raj, A.S. (1967). Studies on the effects of diethyl sulphate on niger (Guizotia abyssinica Cass.). Andhra Agriculture Journal, 14, 4-11. (From Field Crop Abstracts, 1968, 21, 1229.)

HELIANTHUS

H. annuus L.	sunflower
H. bolanderi Gray
H. debilis Nutt.
H. exilis Gray	serpentine sunflower
H. petiolaris Nutt.	sand-hill sunflower

I. Evidence of dormancy

Freshly harvested seeds of H. annuus can show considerable dormancy (1,2,5,7,9,11,14-18,20,21). This causes problems for breeding programmes (7). Dormant seeds require between 2 and 7 weeks after-ripening at room temperature to lose dormancy (2,5,11,14,16,17,21) and the dormancy of seeds buried in soil can prevent them from germinating for more than 50 years (18). The seeds of the wild species H. bolanderi, H. exilis and H.petiolaris are rather more dormant (8,12,22).

II. Germination regimes for non-dormant seeds

H. annuus

BP; S: 20°/30°C (16h/8h); 25°C; 20°C: 10d (ISTA)

BP: 20°/30°C (16h/8h): 7d (AOSA)

Constant temperatures: 20°C, 25°C, 30°C (6)

Alternating temperatures: 20°/30°C (16h/8h) (6)

H. debilis

BP; S; TP: 20°/30°C (16h/8h); 20°C: 14d (ISTA)

Helianthus spp.

TP: 20°/30°C (16h/8h): 7d (AOSA)

III. Unsuccessful dormancy-breaking treatments

H. annuus

Pre-chill: 3°C, 10°C, 3-7d (5); 5°C, 7-21d (3); 5°C, 28d, in light (18)

Pre-soak: 1-24h (3); 12-72h (21)

Oxygen: (9)

Ethephon: pre-applied, 3,6,23h, 120-480 g/1 (3)

Light: dark, at 20°C, 20°/30°C (16h/8h) (19)

Removal of seed covering structures: excise embryo (18)

Scarification: sulphuric acid (18)

GA₃: (18)

H. exilis

Light: far red, 8h/d, at 20°C, with or without pre-chill, 10°C, 12d (12)

IV. Partly-successful dormancy-breaking treatments

H. annuus

Constant temperatures: 15°C in light (19)

Alternating temperatures: 20°30°C (16h/8h) (19)

Pre-chill: 3°C, 10°C, 1-3d (5); 5°C, 28d, dark, germinate at 15°/25°C (16h/8h) in light, 8h/d (18); 3°C, 7-28d, germinate at 20°/30°C (16h/8h) in light (19); 2-4m (22)

Potassium nitrate: co-applied, 0.2% (5); co-applied, 0.2%, dehulled seeds (5)

GA₃: (21); pre-applied, 24h, up to 1000 ppm (9); pre-applied, 24,48h (10); co-applied, 3 ppm (14); co-applied, 3, 30 ppm, dehulled seeds (13); co-applied, 0.2% (1)

Ethephon: (21); pre-applied, 12-48h, 10-1000 ppm, intact or dehulled seeds (7); co-applied, 25 ppm (14); co-applied, 5, 100 ppm, dehulled seeds (13)

Indoleacetic acid: pre-applied, 24,48h (10)

Hydrogen peroxide: pre-applied, 24h (5)

Pre-soak: 24h (5)

Removal of seed covering structures: (5,7,13,14)

Pre-dry: 30°C, 9d (1); 40°C, 14d (5); 39°C, 16h (7); 39°C, 16h, then ethephon, pre-applied, 6-24h, 50-200 ppm (7); 30°C, 9d, then GA₃, co-applied, 0.2% (1)

Benzyladenine: co-applied, 2, 20 ppm, dehulled seeds (13); co-applied, 2 ppm (14)

H. bolanderi

Pre-chill: 10°C, 12d (8, 12)

Light: red, far red, 8h/d, with or without pre-chill, 10°C, 12d (8,12)

H. exilis

Pre-chill: 10°C, 12d (12)

Light: red, 8h/d, with or without pre-chill, 10°C, 12d (12)

V. Successful dormancy-breaking treatments

H. annuus

Pre-chill, Pre-dry (ISTA)

Pre-chill: 2°-5°C, 60d, germinate at 15°/25°C (16h/8h) (9)

Pre-dry: 35°C, 70d (15); 0°C, 4,9d (5)

GA₃: pre-applied, 24h, 300, 500 ppm (5); pre-applied, 24h, 300, 500 ppm, then pre-dry 0°C, 3d (5)

Removal of seed covering structures: husk, pericarp (3)

Ethrel: co-applied, 25, 50 ppm, dehulled seeds (13); co-applied, 250 ppm (21); pre-applied, 24h, 100 ppm (7)

H. debilis

Pre-chill (ISTA)

VI. Comment

The most dormant seeds of H. annuus require 60 days pre-chilling to promote germination (9). Consequently the treatment prescribed by ISTA (3°-5°C for up to 7 days) is unlikely to be a sufficiently adequate treatment for gene banks. Moreover, in less dormant seed lots a 2 to 3 day pre-chill treatment can reduce germination (3,5). Thus it appears that pre-chill treatments are ruled out for gene bank use. No completely satisfactory dormancy-breaking methods have been found for the wild Helianthus spp.

It is surprising that little work has been done on the effect of the germination test temperature (both constant and alternating) in promoting the germination of dormant seeds of Helianthus spp. It is suggested that gene banks dealing with these species might investigate this topic. In the meantime it is suggested that seeds of Helianthus accessions be tested in rolled paper towels or sand at an alternating temperature regime of 20°/30°C (16h/8h). For many accessions it will be necessary to increase the germination test duration considerably beyond the 7 or 10 days prescribed by AOSA and ISTA respectively and additional dormancy-breaking treatments will also be required. Ethephon is one of the more effective dormancy-breaking agents for H. annuus (7,13,14,20,21): it is suggested that it be co-applied at 100 ppm for all Helianthus spp. accessions with dormant seeds with the additional treatment of removal of seed covering structures from ungerminated seeds after 14 to 21 days in test.

VII. References

1. Blagodyr, A.P. (1979). [A method of determining germination of freshly-harvested sunflower seeds.] Selektsiya i Semenovodstvo, 3, 49-50. (From Seed Abstracts, 1981, 4, 3719.)

2. Clerc, P. (1972). Contribution à l'étude de la dormancy des akènes de tournesol (Helianthus annuus L.). Information Techniques, Centre Technique Interprofessionnel des Oléagineux Mètropolitains, 26, 10-19.

3. Côme, D., Simond-Côte, E. and Rollier, M. (1977). Etude de la germination des semences de tournesol. Information Techniques, Technique Interprofessionnel des Oléagineux Métropolitains, 54, 3-28.

4. Cseresnyes, Z. (1974). Application of the tetrazolium topographical test in the sunflower seed viability determination. In Proceedings of the Sixth International Sunflower Conference, 1974, Bucharest, Romania.

5. Cseresnyes, Z. (1979). Studies on the duration of dormancy and method of determining the germination of dormant seeds of Helianthus annuus. Seed Science and Technology, 7, 179-188.

6. Cseresnyes, Z. (1979). The germination of Helianthus annuus seeds under optimum laboratory conditions. Seed Science and Technology 7, 319-328.

7. Harada, W.S. (1982). The effects of ethephon on dormant seeds of cultivated sunflower (Helianthus annuus L.). Proceedings of the 10th International Sunflower Conference, 1982, Toowoomba, Australia.

8. Jain, S.K., Olivieri, A.M. and Fernandez-Martinez, J. (1977). Serpentine sunflower, Helianthus exilis, as a genetic resource. Crop Science, 17, 477-479.

9. Lane, F.E. (1965). Dormancy and germination in fruits of sunflowers. Dissertation Abstracts, 26-N, 3603-3604.

10. Majid, F.Z., Begum, S. and Rahman, A. (1980). Sunflower as oil seed crop in Bangladesh. VIII. Effects of some hormones on sunflower variety Krasnodarets. Bangladesh Journal of Scientific and Industrial Research, 15, 174-176. (From Seed Abstracts, 1982, 5 2240.)

11. Mehrotra, O.N., Pal, M. and Singh, G.S. (1978). Studies on post harvest dormancy in sunflower seeds. Seed Research, 6, 91-93.

12. Olivieri, A.M. and Jain, S.K. (1978). Effects of temperature and light variations on seed germination in Sunflower (Helianthus) species. Weed Science, 26, 277-280.

13. Udaya Kumar, M. and Krishna Sastry, K.S. (1974). Effect of exogenous application of growth regulators on germinating ability of developing sunflower seed. Indian Journal of Experimental Biology, 12, 543-545.

14. Udaya Kumar, M. and Krishna Sastry, K.S. (1975). Effect of growth regulators on germination of dormant sunflower seeds. Seed Research, 3, 61-65.

15. Wallace, R.N. and Habermann, H.M. (1958). Absence of seed dormancy in a white mutant strain of Helianthus annuus L.. Plant Physiology, 33, 252-254.

16. Zimmerman, D.C. and Zimmer, D.E. (1978). Influence of harvest date and freezing on sunflower seed germination. Crop Science, 18, 479-481.

17. Dighe, R.S. and Patil, V.N. (1980). A note on dormancy in sunflower and the relationship of some seed characters with germination. Seed Research, 8, 91-93.

18. Leather, G.R., Frederick, M.D. and Sung, S.-J.S. (1983). Ecological significance of native wild sunflower seed germination patterns. Plant Physiology, 72, 98.

19. Maguire, J.D. and Overland, A. (1959). Laboratory germination of seeds of weedy and native plants. Washington Agricultural Experiment Station, Circular No. 349, 15 pp.

20. Ruud, R. (1976). The use of ethrel to break dormancy of sunflower seeds in a germination test. Newsletter of the Association of Official Seed Analysts, 50, 43-44.

21. Srivastava, A.K. and Dey, S.C. (1982). Physiology of seed dormancy in sunflower (Helianthus annuus L.). Acta Agronomica Academiae Scientiarum Hungaricae, 31, 70-81.

22. Tolstead, W.L. (1941). Germination habits of certain sand-hill plants in Nebraska. Ecology, 22, 393-397.

LACTUCA

L. biennis (Moench) Fern.	blue lettuce
L. sativa L.	lettuce
L. serriola L. [L. scariola L.]	wild or prickly lettuce

I. Evidence of dormancy

Much of the work which has led to a greater understanding of the way in which light quality and quantity affects seed germination - either promoting germination or inducing dormancy - has used lettuce as the experimental material. Also thermodormancy (failure to germinate at high temperatures) can be a considerable problem for commercial lettuce growers. Consequently the literature devoted to lettuce seed dormancy is considerable. This review is, however, limited to papers which are relevant to the problems facing gene bank staff: what laboratory method(s) will promote germination of all viable lettuce seeds.

II. Germination regimes for non-dormant seeds

L. sativa

TP; BP: 20°C: 7d (ISTA)

TP: 20°C: 7d (AOSA)

III. Unsuccessful dormancy breaking treatments

L. biennis

Constant temperatures: 20°C, dark (22,36); 15°C in light or dark, continuous (22)

Alternating temperatures: 20°/30°C (16h/8h), dark (22) Pre-chill: 5°-8°C, 5d, germinate at 20°C, dark (22)

L. sativa

Constant temperatures: 30°C in dark (3-6,27,29,31)

Pre-chill: 1°-4°C, up to 24h, then tested at 30°C (6)

Pre-dry: 35°C, 7d (27)

Light: far red (6,11,12,34,35); green (9); blue (9)

Carbon dioxide: 0-40% (2)

Cycloheximide: co-applied, 1-100 ppm (10)

p-Fluorophenylalanine: co-applied, 1-100 ppm (10)

Puromycin: co-applied, 1-100 ppm (10)

Hydroxylamine hydrochloride: co-applied, 3.2x10^-4 M (15)

Ammonium chloride: co-applied, 10^-2 M (15)

Potassium nitrate: co-applied, 10^-3 M (15)

Sodium nitrite: co-applied, 10^-3 M (15)

GA₃: co-applied, 100-10000 ppm (11)

Ethephon: co-applied, 1000 ppm (11)

Potassium thiocyanate: co-applied, 1% (33)

Urea: co-applied, 1% (33)

Acetamide: co-applied, 0.5, 1% (33)

Potassium cyanide: co-applied, 0.5% (33)

Allylurea: co-applied, 0.5, 1% (33)

Ammonium sulphate: co-applied, 1% (33)

Asparagin: co-applied, 0.5, 1% (33)

Calcium thiocyanate: co-applied, 0.5, 1% (33)

Potassium ferricyanide: co-applied, 0.5, 1% (33)

Potasium ferrocyanide: co-applied, 1% (33)

Semicarbazide hydrochloride: co-applied, 0.5, 1% (33)

Sodium nitrate: co-applied, 1% (33)

Sodium thiocyanate: co-applied, 0.5, 1% (33)

Sulphuric acid: co-applied, 0.5, 1% (33)

Ammonium nitrite; co-applied, 0.5, 1% (33)

Hydrazine: co-applied, 0.5, 1% (33)

Sulphanilic acid: co-applied, 0.5, 1% (33)

Abscisic acid: pre-applied, 1h, 10^-5, 10^-4 M (35)

Ethanol: pre-applied, 20 min, 4, 8% (24)

Removal of seed covering structures: two outer seed coats (6)

IV. Partly-successful dormancy breaking treatments

L. biennis

Constant temperatures: 20°C in light, continuous (22)

Alternating temperatures: 15°/25°C (16h/8h), dark (22)

L. sativa

Constant temperatures: 20°C in dark or light (27); above 20°C in daylight (7)

Alternating temperatures: 15°/30°C (12h/12h) (20) Pre-chill: 1°C, 1-3d (6);16°-18°C, 1d (6); 6°C, 6d (27); 4°-12°C, 6h (34)

Oxygen: 20-90% (5)

Ethylene: 1-100 ppm, in dark or 15 min red light (1)

Carbon dioxide: 60, 80% (2); 10, 15%, plus ethylene, 1 ppm, in dark or 15 min red light (1)

Thiourea: pre-applied, 16h, 0.5, 1% (2); pre-applied, 8h, 100-1500 ppm (26); co-applied, 10^-2 -10^-4 M (16); co-applied, 0.2% (18,20); co-applied, 0.5% (18,33)

Allyl thiourea: co-applied, 0.5% (32,33)

Ammonium thiocyanate: co-applied, 0.5% (32,33)

Potassium thiocyanate: co-applied, 0.5% (32)

Urea: co-applied, 0.5% (32)

Sodium nitrate: co-applied, 0.5% (32)

Ammonium sulphate: co-applied, 0.1% (32)

Potassium ferricyanide: co-applied, 0.2% (32)

Potassium ferrocyanide: co-applied, 0.5% (32)

Calcium sulphate: co-applied, 1% (32)

Thiosemicarbazide: co-applied, 0.5% (32)

Thioacetamide: co-applied, 0.4% (32)

GA₃: co-applied, 5x10^-5, 5x10^-4, 10^-3 M (4); co-applied, 3x10^-6 M (14); co-applied, 10^-5 M (19); co-applied, 1-50 ppm (10); co-applied, 10-40 ppm (17); co-applied, 100, 200 ppm (18); co-applied, 1-200 ppm (20); pre-applied, 8h, 10-250 ppm (26); pre-applied, 1h, 5x10^-6, 10^-5 M (35); co-applied, 3x10^-6 M, plus kinetin, 5x10^-7 M (14); pre-applied, 8h, 50 ppm, plus thiourea, 1000 ppm (26); pre-applied, 1h, 10^-6 M, then hydrogen cyanide, pre-applied, 1h, 10^-6 M (35)

Kinetin: co-applied, 5x10^-5 M (14,21); co-applied, 5x10^-7 M (14) Hydrogen cyanide: pre-applied, 1h, 10^-6 M, imbibed seeds (35); pre-applied, 1h, 10^-6 M, then GA₃, pre-applied, 1h, 10^-6 M (35)

Potassium cyanide: co-applied, 10^-4 M (15)

Potassium azide: co-applied, 10^-5 M (15)

Catechol: co-applied, 10^-4 -3.2x10^-3 M (16)

Pyrogallol: co-applied, 10^-2 M (16)

Calcium chloride: pre-applied, 20 min, 5x10^-3 M (24)

Ethanol: pre-applied, 20 min, 0.5-4%, imbibed seeds (24); pre-applied, 20 min, 1%, then calcium chloride, pre-applied, 20 min, 5x10^-3 M (24)

Light: red, yellow, orange, 6400 lux (9)

Pre-soak: 2h in light (27); 1-72h in light (31)

L. serriola

Constant temperatures: 15°C in light (36); 23°C in light (37)

Alternating temperatures: 20°/30°C (16h/8h) in light or dark (36); 23°/30°C (24h/24h) in light (37)

Thiourea: co-applied, 0.5%, at 25°C in light, 1560 lux (25)

V. Successful dormancy breaking treatments

L. biennis

Alternating temperatures: 15°/25°C (16h/8h) in light (22); 20°/30°C (16h/8h) in light (22,36)

Pre-chill: 5°-8°C, 5d germinate at 20°C in light (22) Potassium nitrate: co-applied, 0.2%, at 20°/30°C (16h/8h), dark (22)

L. sativa

Pre-chill, (ISTA)

Pre-chill, test at 15°C (AOSA)

Constant temperatures: 3°C (23); 5°C in light (2); 3°-20°C in dark (3); 5°-20°C, low light, 14h/d (29,30); 8°-12°C (6); 10°C in red light or dark (28,31); 10°C, 14°C, in dark or daylight, 14h/d (7); 12.5°C in dark (4); 15°C in dark (1,20); 15°C in light (27); 10°-20°C in light or dark (5); 10°-20°C in dark (8); 15°-22°C in light (13); 20°C, plus 5 min red light, 8.1x10^-5 W cm^-2 (11,12,28)

Pre-chill: 4°C, 1d (34); 4°C, 2-3d (6); 3°C, 2d (23)

Pre-dry: 55°C, 21d (7)

Light: diffuse daylight, fluorescent (2,27);red (8); red, 660 nm, 8 min, applied 2-12h after dark imbibition at constant temperatures below 22°C (5); continuous red light, 4.8x10^-2 W cm^-2 (4); red, 1.5x10^-4 W cm^-2, 10 min (10); 8.1x10^-5 W cm^-2, 5-15 min (11,12); 7x10^-5 W cm^-2, 1-4 min (19); 4.5x10^-4 W cm^-2, 15s (34)

Removal of seed covering structures: inner seed coat (6)

GA₃: co-applied, 50-100 ppm (17); co-applied, 100-1000 ppm (10); co-applied, 3x10^-4 M (14); co-applied, 10^-3 M (19)

GA_4/7: co-applied, 10^-4 M (12)

Thiourea: co-applied, 10^-1 M (16); co-applied, 0.5% (25,32) Threo-chloramphenicol: co-applied, 0.1-0.3%, 10 min red light, 1.5x10^-4 W cm^-2 (10)

L. serriola

Constant temperatures: 20°C, dark (36); 23°C, dark (37)

VI. Comment

The considerable literature on lettuce seed dormancy might provide the impression that it is difficult to achieve full germination of lettuce seeds. This is not so. Full germination of dormant seeds of L. sativa can be achieved by testing at 12° to 15°C in diffuse light or the light regime given in Chapter 6.

Prolonged exposure to higher temperatures may induce dormancy (thermodormancy) whereby the seeds will fail to germinate - even when subsequently removed to a lower temperature. As a precaution imbibing seeds should be placed in the germination test incubator as soon as possible: that is imbibing seeds should not be left at laboratory temperature.

This regime is, however, unlikely to be successful in promoting the germination of all dormant seeds of L. biennis (22) or L. serriola (36,37). It is suggested that seeds of L. biennis be tested for germination at an alternating temperature regime of 20°/30°C (16h/8h) in light, but that seeds of L. serriola be tested in the dark at a constant temperature of 20°C since light inhibits germination in this species (36,37).

VII. References

1. Abeles, F.B. and Lonski, J. (1969). Stimulation of lettuce seed germination by ethylene. Plant Physiology, 44, 277-280.

2. Barton, L.V. and Crocker, W. (1948). Twenty years of seed research at Boyce Thompson Institute for Plant Research. Faber and Faber Limited, London.

3. Berrie, A.M.M. (1966). The effect of temperature and light on the germination of lettuce seeds. Physiologia Plantarum, 19, 429-436.

4. Berrie, A.M.M. and Taylor, G.C.D. (1981). The use of population parameters in the analysis of germination of lettuce seed. Physiologia Plantarum, 51, 229-233.

5. Borthwick, H.A., Hendricks, S.B., Toole, E.H. and Toole, V.K. (1954). Action of light on lettuce seed germination. Botanical Gazette, 115, 205-225.

6. Borthwick, H.A. and Robbins, W.W. (1928). Lettuce seed and its germination. Hilgardia, 3, 275-305.

7. Eewink, A.H. (1977). Influence of temperature on seed dormancy in lettuce. Scientia Horticulturae, 6, 1-13.

8. Elliott, R.F. and French, C.S. (1959). Germination of light sensitive seed in crossed gradients of temperature and light. Plant Physiology, 34, 454-456.

9. Flint, L.H. (1934). Light in relation to dormancy and germination in lettuce seed. Science, 80, 38-40.

10. Frankland, B. and Smith, H. (1967). Temperature and other factors affecting chloramphenicol stimulation of the germination of light-sensitive lettuce seeds. Planta, 77, 354-366.

11. Globerson, D. (1981). Germination and dormancy in immature and fresh-mature lettuce seeds. Annals of Botany, 48, 639-643.

12. Globerson, D., Ginzburg, C. and Zahari, K.A. (1973). Comparative studies of seed germination of two newly isolated lines of Grand Rapids lettuce. Annals of Botany, 37, 699-704.

13. Gray, D. (1975). Effects of temperature on the germination and emergence of lettuce (Lactuca sativa L.) varieties. Journal of Horticultural Science, 50, 349-361.

14. Haber, A.H. and Tolbert, N.E. (1959). Effects of gibberellic acid, kinetin, and light on the germination of lettuce seed. In Photoperiodism and Related Phenomena in Plants and Animals, pp. 197-206. American Association for the Advancement of Science, Washington D.C.

15. Hendricks, S.B. and Taylorson, R.B. (1974). Promotion of seed germination by nitrate, nitrite, hydroxylamine and ammonium salt. Plant Physiology, 54, 304-309.

16. Hendricks, S.B. and Taylorson, R.B. (1975). Breaking of seed dormancy by catalase inhibition. Proceedings National Academy of Science, U.S.A., 72, 306-309.

17. Ikuma, H. and Thimann, K.V. (1960). Action of gibberellic acid on lettuce seed germination. Plant Physiology, 35, 557-566.

18. Kahn, A. (1960). Promotion of lettuce seed germination by gibberellin. Plant Physiology, 35, 333-339.

19. Kojima, H. and Oota, Y. (1980). Promotion by gibberellin of lettuce seed germination as a function of presoaking period. Plant and Cell Physiology, 21, 561-569.

20. Kretschmer, M. (1978). Temperature and lettuce seed germination. Acta Horticulturae, 83, 167-173.

21. Leff, J. (1964). Interaction between kinetin and light on germination of Grand Rapids lettuce seeds. Plant Physiology, 39, 299-30

22. Lincoln, W.C. Jr. (1981). Laboratory germination of Lactuca biennis - blue lettuce. Newsletter of the Association of Official Seed Analysts, 55, 30-31.

23. Margaris, N.S. and Fiakou, E. (1974). Low temperature effect on lettuce seed dormancy. Scientia Horticulturae, 2, 209-210.

24. Pecket, R.C. and Al-Charchafchi, F. (1978). Dormancy in light-sensitive lettuce seeds. Journal of Experimental Botany, 29, 167-173.

25. Raleigh, G.I. (1943). The germination of dormant lettuce seed. Science, 98, 538.

26. Sarma, C.M. and Chakraborty, P. (1977). Effect of gibberellic acid and thiourea, singly and in combination, on the germination of lettuce seeds. Indian Journal of Agricultural Sciences, 47, 18-21.

27. Shuck, A.L. (1934). Some factors influencing the germination of lettuce seed in seed laboratory practice. New York State Agricultural Experiment Station, Technical Bulletin No. 222.

28. Takeba, G.O. and Matsubara, S. (1976). Analysis of temperature effect on the germination of New York lettuce seeds. Plant and Cell Physiology, 17, 91-101.

29. Thompson, P.A. (1973). Geographical adaptation of seeds. In Seed Ecology (ed. W. Heydecker), pp. 31-58, Butterworths, London.

30. Thompson, P.A., Cox, S.A. and Sanderson, R.H. (1979). Characterization of the germination responses to temperature of lettuce (Lactuca sativa L.) achenes. Annals of Botany, 43, 319-334.

31. Thompson, R.C. (1938). Dormancy in lettuce seed and some factors influencing its germination. U.S.D.A., Technical Bulletin, No. 655, 20pp.

32. Thompson, R.C. and Kosar, W.F. (1938). Germination of lettuce seed stimulated by chemical treatment. Science, 87, 218-219.

33. Thompson, R.C. and Kosar, W.F. (1939). Stimulation of germination of dormant lettuce seed by sulfur compounds. Plant Physiology, 14, 567-573.

34. VanDerwoude, W.J. and Toole, V.K. (1980). Studies of the mechanism of enhancement of phytochrome-dependent lettuce seed germination by pre-chilling. Plant Physiology, 66, 220-224.

35. Zagorski, S. and Lewak, S. (1983). Interactions between hydrogen cyanide, gibberellin, abscisic acid and red light in germination of lettuce seeds. Physiologia Plantarum, 59, 95-98.

36. Maguire, J.D. and Overland, A, (1959). Laboratory germination of seeds of weedy and native plants. Washington Agricultural Experiment Station, Circular No. 349, 15 pp.

37. Rogers, B.J. and Stearns, F.W. (1955). Preliminary studies on the germination of weed seeds. Proceedings of the North Central Weed Control Conference, 12, 7.

PARTHENIUM

P. argentatum Gray	guayule
P. hysterophorus L.

I. Evidence of dormancy

Freshly harvested seeds of P. argentatum can show considerable dormancy (1,2,5) and require 6-12 months after-ripening at room temperature before dormancy is lost.

II. Germination regimes for non-dormant seeds

P. argentatum

Constant temperatures: 25°C in light (1); 26°C in light (5,6)

Alternating temperatures: 20°/30°C (17h/17h) (1,3)

III. Unsuccessful dormancy-breaking treatments

P. argentatum

Pre-chill: 4°-5°C, up to 60d (1)

Vatsol OS: pre-applied, 20h, 0.01-0.5% (1)

Formaldehyde: pre-applied, 10 min, 2% (1)

Oxygen: pre-applied, 2h, 100% (1) pH: pre-applied, 2h, low (1)

IV. Partly-successful dormancy-breaking treatments

P. argentatum

Constant temperatures: 25°C (1,5)

Alternating temperatures: 20°/30°C (17h/7h) (1,2,3)

Light: continuous (1,3); 3-4d (2,3); light/dark (14h/10h) (5)

Potassium nitrate: pre-applied, 20h, 0.5% (1)

Sodium hypochlorite: pre-applied, 2h, 0.5-1% (2); pre-applied, 1.5% (1); pre-applied, 6h (3)

Removal of seed covering structures: pericarp (1); puncture (1); chaff (6); chaff, then pre-soak, 8h (6)

Pre-soak: 8h (6); 20h (1); 4-24h (5); 18h, then calcium chlorite, pre-applied, 2-4h, 1-7% (1); 18h, then sodium chlorite, pre-applied, 1,2h, 1-2% (1); 18h, then mercuric chloride dissolved in ethanol, pre-applied, 1 min, 0.2% (1); 18h, then hydrogen peroxide, pre-applied, 20h, 1.5-5% (1); 18h, then perchloric acid, pre-applied, 2h, 1.5% (1); 18h, then nitric acid, pre-applied, 2h, 1% (1); 18h, then sulphuric acid, pre-applied, 1 min, 95% (1); 18h, then potassium dichromate, pre-applied, 2h, 0.5% (1); 8h, then sodium hypochlorite, pre-applied, 2h, 0.25-2% (5); 8h, then GA₃, pre-applied, 2h, 200 ppm (5)

P. hysterophorus

Alternating temperatures: 4°/15°C, 10°/15°C, 7°/18°C, 13°/18°C, 13°/24°C, 19°/24°C, 25°/30°C, 28°/33°C, 31°/36°C (16h/8h) (7)

Light: dark (7)

V. Successful dormancy-breaking treatments

P. argentatum

Removal of seed covering structures: fruit and seed coat (1): puncture seed coat, scarify embryo (1)

Pre-wash: 12-18h, then sodium hypochlorite, pre-applied, 2h, 1.5%, germinate at 20°/30°C (17h/7h) in light (1,4); 8h, then 200 ppm GA₃ plus 1% sodium hypochlorite, pre-applied, 2h, germinate at 26°C in light, 14h/d (5)

GA₃: pre-applied, 6h, 1000 ppm (3)

P. hysterophorus

Alternating temperatures: 16°/21°C (16h/8h), dark (7); 19°/30°C (16h/8h), dark (7); 25°/36°C (16h/8h) in light, 16h/d (7)

VI. Comment

A single application of GA₃ is able to break dormancy in partially dormant seeds of P. argentatum but is unlikely to be successful for freshly harvested seeds. Sodium hypochlorite pre-applied singly at 1.5% or at 1% combined with GA₃ at 200 ppm is effective for promoting germination in freshly harvested seeds but is unfortunately detrimental to less dormant seeds (2,5). Whilst light treatments promote the germination of dormant seeds of P. argentatum (1-3), the effect on the germination of dormant seeds of P. hysterophorus appears to be mo re equivocal; promotion by light has been observed in a few temperature regimes, but inhibition of germination by light has been observed in the majority of temperature regimes investigated (7).

Consequently it is suggested that seeds of both species be tested in an alternating temperature regime of 20°/30°C (16h/8h), but that the light regimes should differ with seeds of P. argentatum being tested in the light and seeds of P. hysterophorus being tested in the dark Pre-washing of the seeds may be advantageous, and it is suggested that the seed covering structures be removed from ungerminated seeds in test and that the seeds then be pricked and returned for further testing.

VII. References

1. Benedict, H.M. and Robinson, J. (1946). Studies on the germination of guayule seeds. U.S.D.A., Technical Bulletin No. 921, 48pp.

2. Emparan, P.R. and Tysdal, H.M. (1957). The effect of light and other factors on breaking the dormancy of guayule seeds. Agronomy Journal, 49, 15-19.

3. Hammond, B.L. (1959). Effect of gibberellin, sodium hypochlorite, light, and planting depth on germination of guayule seeds. Agronomy Journal, 51, 621-623.

4. McCallum, W.B. (1929). Method of treating and sowing guayule seed. U.S. Patent No. 1,735,835, U.S. Patent Office, Official Gazette, 388, 520.

5. Naqvi, H.H. and Hanson, G.P. (1980). Recent advances in guayule seed germination procedures. Crop Science, 20, 501-504.

6. Naqvi, H.H. and Hanson, G.P. (1982). Germination and growth inhibitors in guayule (Parthenium argentatum Gray) chaff and their possible influence in seed dormancy. American Journal of Botany, 69, 985-989.

7. Williams, J.D. and Groves, R.H. (1980). The influence of temperature and photoperiod on growth and development of Parthenium hysterophorus L. Weed Research, 20, 47-52.