The Crop

2.1. History and development of the sugar beet as crop plant

Like all cultivated beets, the sugar beet (Beta vulgaris L. ssp. altissima) plant was derived from wild beet (Beta vulgaris, probably Beta vulgaris L. ssp. maritima (L.) THELLG) at first as beetroot or Mangold. Mangold is testified as crop plant down to the period of classical antiquity (1) by written documentation of the Greek comedy poet Aristophanes (448-388 BC). The oldest illustration of mangold in "De Materia medica"(2) shows that leaves are better developed than the root. According to Dioskorides (2), mangold was used as food and as officinal plant for interior and exterior applications. Optimal cultivation conditions for mangold were given already by the Roman poet Palladius (4th century AD) in his work "Opus agriculturae" (3): " It likes tender, fat topsoil. It is picked when 4 to 5 leaves are developed after having smeared fresh manure around the root. It succeeds best when fertilised and the soil around is hacked frequently."

Clearly, the sweetness of Beta-roots explains the special position of white beets that mangold or beet occupy as sugar beet in world agriculture and economy today. Already the Greek philosopher and natural scientist Theophrastus (372-286 BC) points to the sweet taste of mangold roots in "Historia plantarum" where he describes about 500 plant species. Andreas Sigismund Marggraf (1709-1782 AD) remembered the historical indications about beetroot sweetness (4). He proved that beetroots contained 3-4% of the sugar completely identical to the sugar well known and prepared from sugar cane (4). Franz Carl Achard (17531821) carried out more thorough studies on the cultivation of sugar containing domestic plants and of Beta-roots in particular (5). He was able to increase sugar yield of his plants to around 8% and put into operation the world's first beet sugar plant near Cunern in Silesia in 1801/1802. For Achard one essential condition for sugar production was efficient beet cultivation. Of course, it is beyond the scope of this article to outline Achard's cultivation guidelines and the certainly even more efficient today's cultivation methods that are summarised elsewhere (see ref. 1 for a review). Classical breeding and efficient cultivation methods have resulted in sugar beet varieties that contain up to 15 to 20 % (relative to fresh weight) of sucrose within their taproots today (6).

2.2. Anatomy of beet storage tissue

Sugar beet is a biennial plant that remains vegetative in the first year and develops a vigorous leaf rosette as assimilate source and a thick taproot as strong sink for sucrose, the long distance transport and storage form of photosynthates in sugar beet. In the second year of its life cycle, the sugar beet plant sprouts and forms its reproductive organs utilising the energy that has been stored as sucrose within the taproot storage parenchyma cells the preceding year. The anatomy of so-called beet roots from Chenopodiaceae is characterised by its anomalous growth. A cross section through this storage organ shows rings of conducting bundles formed by a series of supernumerary concentric cambia (7). Twelve to fifteen cambial layers are formed already early in development. Already in young sugar beets, about six of these cambial layers become visible early during their ontogenetic development and may contribute 75% to the final cross sectional area of the beet according to Milford (8). The meristematic cells produce vascular bundles and parenchyma cells so that the vascular bundles are embedded within layers of small parenchyma cells that are separated from each other by layers of large parenchyma cells. The smaller parenchyma cells correspond in part to phloem and xylem parenchyma. The large parenchyma cells build up what is generally considered as the storage parenchyma.

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