En France, la production marchande, limitée à moins de 1 000 t, est localisée entre Lyon et Vienne. Elle est plus développée en Italie (15 000 t), dans les régions du Piémont et de la Toscane, et en Espagne (12 000 t), dans la région de Valence.
Péron
carence
Absence, apport insuffisant, indisponibilité ou défaut d'assimilation d'une substance nécessaire à la croissance et au développement d'une plante ou d'un animal.
Physiol. animale.
Chez les animaux, une carence entraîne généralement une diminution de production (moins de lait, moins d'œufs...) et des troubles pathologiques plus ou moins graves. On distingue les carences d'apport (élément inexistant ou en quantité insuffisante), les carences d'utilisation (défaut de la digestion ou de l'assimilation, qui empêche l'élément, pourtant présent en quantité suffisante, d'être assimilé), les carences conditionnées (un excès d'un autre élément augmente les besoins en l'élément considéré, qui se trouve alors en position déficitaire si un apport complémentaire n'est pas prévu). Les carences faibles sont appelées subcarences ; très difficiles à déceler, elles réduisent l'efficacité de la transformation des aliments en produits animaux.
Physiol. végétale.
Les carences végétales peuvent résulter d'une trop faible concentration de l'élément dans le sol : ce sont les carences primaires. Mais, le plus souvent, la carence se développe à la suite d'une indisponibilité plus ou moins sévère de l'élément : il s'agit alors d'une carence induite. Ces carences entraînent des troubles physiologiques qui se manifestent par un développement ralenti, une malformation des organes végétatifs ou reproducteurs, des nécroses de la tige des bourgeons ou des racines, une décoloration ou coloration anormale du feuillage. Un premier diagnostic peut donc être porté par l'examen de ces symptômes. On procède ensuite à l'analyse de terre : différentes méthodes existent pour déterminer le degré de disponibilité pour la plante des différents éléments minéraux dont elle a besoin.
Les carences induites sont le plus souvent occasionnées par une valeur de pH non adaptée ou un déséquilibre minéral (la présence d'un élément en trop grande quantité gêne l'assimilation d'un autre). Dans les sols à pH élevé (sols calcaires) on observe fréquemment des carences relatives au fer, zinc, cuivre, manganèse et bore. La carence en molybdène apparaît dans les sols acides. Dans les sols bien cultivés, les carences en éléments majeurs (azote, phosphore, potassium) s'observent rarement ; elles proviennent le plus souvent d'une fertilisation mal conduite, problème auquel il est aisé de remédier. Pour les carences primaires en oligoéléments, on réalise des apports sous forme de pulvérisation foliaire, très rapidement efficaces car l'élément est absorbé par la feuille. Certaines carences induites en oligoéléments sont plus difficiles à corriger car il ne suffit pas d'apporter l'élément incriminé (le défaut du sol se reporte alors sur l'élément ajouté). La correction passe par une modification du pH (chaulage) ou des apports sous forme organique de l'élément, qui, de ce fait, ne subit pas de blocage par le sol (formes chélatées du zinc). Dans les cas les plus délicats (chlorose ferrique sur les arbres fruitiers), on utilise des porte-greffe résistants.
Roger-Estrade
carie du blé
Maladie du blé provoquée par le champignon Tilletia caries.
Le blé carié a un aspect caractéristique : sa tige a une coloration vert intense persistante ; l'épi est vert foncé avec des reflets bleuâtres avant la maturité et il présente à maturité un port dressé avec une allure ébouriffée ; le grain, visible entre les glumes, est globuleux, rempli d'une poudre noire, et dégage une odeur de poisson pourri. Les farines obtenues avec des grains cariés sont très dépréciées. La contamination du blé s'effectue au moment de la récolte, à partir de grains infectés par des spores du champignon. Le parasite pénètre dans la plantule au moment de la germination.
Traitement.
Le traitement des semences par des fongicides appropriés constitue une méthode de lutte efficace, qui a pratiquement fait disparaître cette maladie, contre laquelle la plus grande vigilance s'impose cependant.
Raynal
carotène
Pigment lipidique précurseur de la vitamine A.
LAPIERRE
caroténoïde
Pigment soluble dans les solvants organiques, de couleur jaune, orange ou rouge, élaborés par les végétaux supérieurs.
Le b-carotène (ou provitamine A) des feuilles des plantes vertes participe à la capture de l'énergie lumineuse et améliore ainsi l'efficacité de la photosynthèse. Chez les animaux, ce pigment apporté par l'alimentation est clivé en vitamine A (ou rétinol). La vitamine A agit sur la croissance et sur la vision. Associée à une protéine, l'opsine, elle donne la rhodopsine, pigment photosensible nécessaire à la vision.
Les caroténoïdes (lycopène de la tomate, carotène de la carotte...) sont responsables de la couleur des fruits et légumes, des fleurs, des feuilles à l'automne, du jaune de l'œuf et du beurre. Leurs propriétés antioxydantes suscitent beaucoup d'intérêt pour la santé humaine (ils pourraient participer, avec les molécules phénoliques, à la protection contre les maladies cardiovasculaires et les cancers).
LAPIERRE
carotte
1. Plante bisanuelle spontanée dans de nombreuses régions du monde, cultivée pour sa racine comestible (espèce Daucus carota, famille des Apiacées). 2. Racine de cette plante.
L'Afghanistan est considéré comme le premier centre de domestication de la carotte. Des plantes à racines de couleur jaune y ont été obtenues par mutation naturelle dans les populations cultivées locales, qui étaient toutes à racine violacée ou pourpre. À partir des types à racine jaune, dont la culture s'est généralisée en Europe du Nord-Ouest, ont été créées progressivement les variétés à racine rouge-orangé, riches en carotène. Les types à racine blanche sont des mutants issus des types à racine jaune. La carotte est utilisée en alimentation humaine et animale.
Cycle de vie.
En 1re année, la plantule évolue en une rosette de feuilles finement découpées, et développe une racine pivotante tubérisée en l'absence d'obstacles tels que pierres, pailles ou résidus de culture. En 2e année, la plante émet une hampe florale fortement divisée mais relativement basse. Les fleurs, disposées en ombelle, sont blanches ou rosées, à l'exception de la fleur centrale, généralement pourpre et très grande. La racine est consommable jusqu'à l'apparition de la hampe florale, moment où elle devient fibreuse.
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