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Améliorations variétales au bénéfice des consommateurs

jury label rouge dahlia 2008 (C Secq)Chaque année dans le secteur horticole, de nouvelles variétés, voire de nouvelles espèces, sont proposées à la vente. Variations de port, de couleur, de goût, de précocité, sont les caractéristiques les plus visibles pour le consommateur. Tout aussi importantes sont les tolérances à des maladies, à des insectes, à des stress environnementaux : sécheresse, salinité…
L’objet de cet article n’est pas de présenter les méthodes employées par les sélectionneurs, mais de tenter d’expliquer les causes et les conséquences de cet enrichissement permanent du patrimoine variétal.

De l’introduction raisonnée à la création variétale
L’horticulture ornementale a toujours cherché à diversifier son offre en introduisant des espèces venant d’autres pays ou continents. Il est d’ailleurs fort intéressant de retracer l’histoire de ces introductions, dont la période forte est celle des grandes découvertes, du temps de Christophe Colomb, et qui se poursuit de nos jours : il suffit de prendre pour exemple la famille des protéacées… L’introduction, et surtout l’introduction raisonnée, comme celle qui voit le jour actuellement, est un travail de domestication. Il s’agit de rechercher quelles espèces s’adaptent à nos climats, d’étudier leur comportement sous différents environnements, de rechercher leur adaptabilité éventuelle à la culture en conteneurs. À ce stade, en général, la variabilité génétique au sein de l’espèce est peu prise en compte, le choix des individus retenus est fait sur la base des caractéristiques phénotypiques d’apparence, d’allure, de port ou de croissance. Vient ensuite une mise au point des méthodes de propagation en recherchant des taux de multiplication élevés, et pour cela, toutes les méthodes habituelles des pépiniéristes sont mises en oeuvre. La décision de commercialiser n’interviendra que si ces étapes sont franchies avec succès. Aujourd’hui, et dans le cadre du raisonnement sur l’agriculture durable, de nouveaux critères sont de plus en plus fréquemment pris en compte, avant d’introduire et de diffuser de nouvelles espèces. Une attention particulière peut être apportée à de faibles exigences en eau dans les régions méditerranéennes. Tel est le cas à la Villa Thuret, jardin botanique situé sur le cap d’Antibes, où toute espèce candidate à l’introduction reçoit en tout et pour tout un arrosage l’année de son implantation. Le caractère potentiellement invasif de la nouvelle espèce doit être apprécié avec soin.

Les raisons sont multiples :
- la concurrence entre espèces risquerait d’éliminer des espèces endémiques,
- le développement incontrôlé de semis risquerait de modifier les paysages,
- les espèces introduites sont souvent peu sensibles aux parasites et aux prédateurs ; si leur développement est important, il n’y aura pas de régulation biologique. En contrepartie, cette faible sensibilité aux parasites est un atout, au moins temporaire, des plantes nouvellement introduites et domestiquées car certains d’entre eux peuvent s’adapter à un nouvel hôte. La phase suivante de cette domestication est l’exploration de la variabilité génétique au sein de l’espèce pour développer par hybridation des formes nouvelles différentes des plantes parentales, qui seront ensuite choisies, multipliées et proposées à la vente. De nos jours, les introductions concernent essentiellement les espèces arbustives ou buissonnantes, certaines potées fleuries à multiplication végétative. Néanmoins l’enrichissement du nombre de variétés provient essentiellement de nouvelles créations génétiques.

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Yvette Dattée
Présidente du conseil scientifique de la SNHF
Jardins de France Novembre 2009


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