Botanical Files on Lettuce (Lactuca sativa). On the chance for flow between wild and cultivated gene Lettuce (Lactuca sativa L. including L. serriola L., Compositae) and the generalized implications for risk-assessments on genetically modified plants by 12 2 ,3 F.T.+Frietema de Vriesi R. van der Meijdeni and W.A. Brandenburg , dit onderzoek werd door het Ministerie De opdracht tot gegeven van Volkshuisvesting, Ruimtelijke Ordening & Milieu, Directoraat-Generaal Milieu, Directie Stoffen, Veiligheid, Straling. De tekst het zal in de VROM/DGM Risico- van rapport verschijnen publicatiereeks beoordeling genetisch gemodificeerde organismen. This commissioned the Netherlands of report was by Ministry Housing, Spatial Planning and Environment, Directorate General for the Environment, Directorate for Chemicals, External Safety and Radiation Protection, P. O. Box 450, 2260 MB Leidschendam, The Netherlands. It will be published in the series Risk Assessment Genetically Modified Organisms. 1) Formerly F.T. de Vries 2) Rijksherbarium/Hortus Botanicus, Slate University Leiden, P.O. Box 9514, 2300 RA Leiden, The Netherlands 3) Centrum voor Plantenveredelings- en Reproduktieonderzoek, CPRO-DLO, P.O. Box 16, 6700 AA Wageningen,The Netherlands Contents Summary 3 1. Introduction 3 2. Lactuca serriolaL. and L. serriola L. in Western 6 Historical part: Europe... Introduction 6 Terminology 6 The genus Lactuca L 7 Genetics 8 Ancestors 9 Characters 9 3. Domestication of Lettuce 11 Introduction 11 Early domestication 11 of the different of cultivated lettuce Further development groups 12 4. Field trial 13 Introduction 13 Material 15 Methods 15 Observations 16 Herbarium material 16 Photography and microscopy 16 5. Results 17 Introduction 17 Results herbarium study 17 Results field trial 17 6. Discussion and conclusions 25 7. Towards European Botanical files 27 Introduction 27 European plant geographical regions 28 Towards D 28 European p(jf-codes Summary of the chances for gene flowper region 31 An D for Lettuce Lactuca 3l example: European p(jf-codes ( sativa) Discussion and conclusions 32 Literature 33 Appendices 35 2 Gorteria Supplement 2 (1994) Botanical Files on Lettuce (Lactuca sativa) Summary In Botanical Files, a study of the real chances for gene flow from cultivated plants to the wild a ³7 of codes (D was introduced (see text box D are indications of al- system dispersal p df) p df). They cultivated the wild be deduced from ready occurring gene flow from plants to flora, as can herbarium collections and florisdc archives. These codes apply to the Netherlands only. One of the of which the real chances for flow could be determined, because of crops gene not uncertainties regarding the relationship between the cultivated plant and its wild relatives, is Lettuce (Lactuca sativa L.). Its relationship with the wild L. serriola L. is accepted to be very close, but the 350 species are considered to be distinguishable. In a field trial, using specimens from 67 genetically different populations, the distinction between the two species proved to dependlargely on character states usually connected to domestication, like absence or presence of prickles, retention of achenes, leaf texture and colour. The that both wild and cultivated lettuce be considered the consequences are must to belong to ‘domesticated’ states ‘wild’ same species. The finding of some character in lettuces indicates an al- and the D is ready gene flow between cultivated lettuce and the wild flora, jf-code adapted ongoing p( accordingly, indicating a substantial chance for gene flow from cultivated lettuce to its wild relative in the Netherlands. to Ifthe of codes as in Botanical Files is extended D df-codes scope Dispersal Europe, European p are needed. In this report a model is proposed using a plant geographicaldivision of Europe into six For each six D the chances for flow to vegetational regions. species pdf-codes, summarizing gene each of the regions, should be developed. For the major part of the species this can be done using the information already present in national herbarium collections. 1. Introduction This Botanical Files is continuationof the Botanical Files report, on Lettuce, a report which presented the possibilities for gene flow from cultivated plants to the wild 37 for of flora of the Netherlands. Botanical Files was prepared the Ministry Housing, and be used tool for the evaluation of Spatial Planning and Environment, can as a risk assessments for Genetically Modified Organisms (GMO's). 42 were studied, decide which In the previous report crop species to (floristic) factors should be considered when assessing the possibility for gene flow from a certain cultivated plant to the wild flora. This question had become an urgent one in the public discussion on the introductionand use of GMO's. Gene flow There in which acultivated flow to the wild flora: are two ways plant may cause gene wild itself. So the chances for by hybridizing with wild relatives and by running gene flow depend both on the degree of relationship of the cultivated plant with its closest wild relative, and on the fitness of cultivated plants in a more or less natural, i.e., non-cultivated environment. Gorteria Supplement 2 (1994) 3 It must be stated explicitly, that the nature of the inserts in GMO's was not included in the study, nor the effect of the inserts on the organisms themselves. The study confined to the flow, which be inferred from was already occurring gene can the distribution of in the wild in the Netherlands and in the and plants present now past, from their relationships with cultivated plants (see text box Gene flow). During the study for Botanical Files it became clear, that taxonomic relationships of cultivated plants and their relatives in the wild, must be fully understood before the determined. Of real chances for geneflow can be most of the cultivated plants in the study, theirrelationship to the species of the same genus belonging to the wild flora of the Netherlands could be determined without doubt. Of some species however, the exact relationship with wild relatives could not be ascertained because of lacking or incomplete information.For these species furtherresearch was recommended. is Garden One of the crops suited for this purpose Lactuca sativa L., lettuce, culti- small but scale in the Netherlands, both indoors vated on a wide-spread as a green- house vegetable, and outdoors. It is considered to be closely related to Prickly Let- tuce ( Lactuca serriola L.), which is a component ofthe wild flora of the Netherlands. Prickly lettuce is generally found on sunny, more or less dry, rich, usually calcif- erous and/or stony places, and is associated with soil disturbance. It was rare in the Netherlands until the first half of this century, but since the 1960's it has suddenly 12 13 23 41 become invasive in the Western part of the Netherlands. The same phe- 5 nomenon was recently recorded in Warwickshire, Britain. On the other hand, Garden lettuce is assumed to be only occasionally found in the wild, and then usually in 22 unnatural habitats, like rubbish dumps, waysides, old allotments, etc. Both species are considered to be predominantly self-fertilizing. considered bluish leaves Prickly lettuce (Fig. 4, p. 21) is usually to have green with a row of prickles on the midrib, and with cauline leaves usually twisted to the vertical plane. The capitula are grouped to a rich pyramidal or plume-like inflores- reflexed involucral leaves. Garden lettuce is de- cence, and have (Fig. 5, p. 21) scribed as having often light-coloured, glabrous leaves, forming large heads, and with cauline leaves not twisted to the vertical plane. The capitula are grouped to a flat-topped, umbel-like inflorescence, and have erect involucral leaves. Because this is the commonly held opinion of Garden lettuce, a wild growing lettuce with yellowish green leaves and no prickles will be considered to be an escape, whereas an observation of a vegetative or poorly flowering specimen of a more or less prickly, bluish-green cultivar willbe recorded as wild. Because taxonomists on wild plants are usually not familiar with the variation within cultivatedplants, escapes resembling wild plants can be overlooked. This implies that the recorded number of escaped cultivated lettuce in the Netherlands is low, probably lower than it actually is. of flow from lettuce This has implications for the assessment gene cultivated to noticed will be recorded the wild flora. If the actual escapes are not as such, they as this wild, and therefore as natural. Without knowledge, the informationin literature and the herbarium would yield the following D jf-code: p( Dp = 3 for a wild relative of a differentspecies Dd = 2 for occasional escapes, but no lasting populations Df = 2 for an Hour Block Frequency of6 for Prickly lettuce 4 Gorteria Supplement 2 (1994) D df-codes Summary p 37 In the report Botanical Files a code was developed to summarize the information chances for the flow from culdvated the wild flora on already occurring gene plants to of the Netherlands: D It is a code, codes for pcjf. three-digit combining Dispersal by Pollen ), and a of Distribution of the (Dp Dispersal by Diaspores (Dj) Frequency code for the closest wild relative (Df). The higher the a particular crop, higher the flow from that chances for gene crop. Pollen (D ) is related to the taxonomic of the in- Dispersal by p relationship species volved. This dispersal will only have effect if pollen lands on a receptive stigma of a wild relative. Then in combination between hybridization may occur, resulting a new wild and cultivated plants. 0: No wild species from the same genus native to the Netherlands Wild of the native the 1: species same genus to Netherlands; hybrids impossible 2: Hybrids possible, spontaneous hybrids not found in the wild 3: Spontaneous hybrids with different species found in the wild 4: Crosses with same species in the wild possible but undetectable 5: Crosses with both the same and another species in the wild possible Dispersal by Diaspores (Dj) is related to the dispersal capacity of the diaspores of the cultivated plant, and to the fitness of individuals resulting from these diaspores, which might lead to populations in the wild.