Beta vulgaris is a biennial, herbaceous and dicotyledonous plant that on an average takes two years to complete its life cycle. The crop needs a timeframe of close to 140-160 to up to 200 days as an ideal growth period. The first year of cultivation is marked by vegetative growth followed by shoot elongation i.e. bolting and flowering after being exposed to cold temperatures over winter and subsequently resulting in production of seeds. Artificial selection to achieve breeding goals over the past decades has resulted in a number of major cultivated types, each being utilized in a multitude of ways. Cultivated beets are sub categorized into four agriculturally relevant cultivars – leaf beet (chard), sugar beet, garden beet and fodder beet groups within the genus Beta (Ford-Lloyd and Williams 1975; Kole 2011; Lange et al. 1999). The end of the eighteenth century marked an initial emergence when economically viable lines showing accumulation of sugar in the storage root were selected from crosses made with fodder beet and chard (Dohm et al. 2014; Fischer 1989). The ‘Weiße Schlesische Rübe’, is considered the ancestor of all sugar beets from today (Fischer 1989). The crop is believed to have originated from Asia and is now a staple for sugar production in most geographically temperate regions of the world.
In the initial growth stages of the plant, a significant amount of sugars are stored in the leaves. However, as the plant progresses through the vegetative stage, a considerable amount is dedicated towards an array of growth processes. In the subsequent growth stages, vegetative growth deaccelerates and results in a systematic relocation of sugars to the storage root. Root size and sucrose content are direct pointers of sugar yield. This is closely regulated by a number of environmental factors which include climate, temperature, photoperiodism, soil fertility; specifically nitrogen nutrition (Nevins and Loomis 1970), and availability of water. Over the course of last decades, effective breeding programs have resulted in sugar content steadily increasing in today’s cultivars. However, sugar yield and root dry mass are negatively correlated (Gartland et al. 1990). Other agronomic traits like pathogenic resistance, improved taproot yield, monogermy and bolting resistance have been successfully selected for (Biancardi et al. 2010). Modern day cultivated Beta vulgaris is highly heterogenous and has been bred as a product of complex crosses between root and leaf varieties. Its tendency of cross-pollinating and self-incompatibility (Owen 1942) usually hinders application of conventional methods such as heterosis (on the basis of cytoplasmic male sterility), inbreeding, polyploidy, phytopathology, interspecific hybridization, etc. in breeding research (Atanassov 1986). The regulation of flowering time, specifically delayed onset of bolting and flowering continues to be a major agronomic objective in breeding B. vulgaris. The annual behavior is characterized by flowering under LD conditions without the requirement for vernalization. The wild ssp. maritima (sea beet) from which current cultivars have originated, is known to display this habit (Jung et al. 1993). Modern day domesticated cultivars of beets are grown as per a strict biennial cycle. For production of sugar, they are harvested in the first year. In cold temperate climates, they are sown in spring and harvested in the autumn of the same year when the plant is still in the vegetative state i.e. when the sugar content in the root is the highest for sugar beets and foliar growth is profuse for leaf beets. Entering the generative stage requires the plant to be exposed to a period of cold temperature i.e. vernalization combined with LD conditions (Biancardi 2005). Vernalization is followed by bolting i.e. the elongation of the main stem/shoot. This marks the transition of the plant from the vegetative to generative phase. When the economic motive is sugar production, bolting and consequent flowering is avoided. Delayed onset of flowering is usually a strong indicator towards increased root biomass and foliar growth in B. vulgaris. It is believed that autumn sown beets are expected to bring significantly higher yields than conventional spring sown beets. In order for such a scenario to materialize, a state of continuous growth during an extended vegetative growth period is quintessential (Hoffmann 2017). In order for these so called ‘winter beets’ to bring economic gains, there must be a manifestation of bolting resistance genes that effectively result in bolting delay even after having experienced the cold winter that accounts as vernalization. Experiments have been done to analyze sugar storage and yield during an extended growth period to evaluate if sugar beet has the potential to generate the theoretically expected yield increase (Schnepel and Hoffmann 2016). Winter sugar beets sown in autumn could theoretically increase dry matter yield by 26 % when compared with spring sown beets due to a longer duration of light absorption experienced (Hoffmann and Kluge-Severin 2010).