Bolting in sugar beet (Betavulgaris subsp. Vulgaris var. Altissima d"oll): triggering, genetic mechanisms and prevention (review)

Sugar beet is a significant crop that is used in the production of sugar, alcohol, livestock feed, confectionery, etc. Sugar beet is a biennial plant that form a root-crop in the first year. In the second year, after winter storage, it produces a bolt with inflorescences. Bolting refers to the ability to form both peduncle and flowers within the first year of life. The formation of bolts in sugar beets is triggered by vernalization (exposure to low positive temperatures) and long daylight hours. Flowering is significant in beet-growing regions with cold springs and long daylight hours as it can result in reduced yield and sugar content. From a genetic perspective, flowering is controlled by a complex system of genes that regulate the transition from the vegetative phase to the generative phase of development. The interaction between the BvBTC1 and BvBBX19 genes plays a central role in this process. The functional products of these genes stimulate the expression of the flowering inducer gene BvFT2 and inhibit the expression of the flowering repressor gene BvFT1 (N. Dally et al., 2018). In the beet genome, several Arabidopsis orthologue flowering genes have been identified. These genes are characterized by differential expression and methylation, which are influenced by vernalization and vary between flowering-resistant and non-flowering genotypes (M.-V. Trap-Gentil et al., 2011; Z. Pi et al., 2021). The main physiological regulator of flowering in sugar beets is gibberellic acid, which is also involved in vernalization through the regulation of synthesis regulator genes (E. Mutasa-Gottgens et al., 2009). The primary methods for controlling flowering involve implementing suitable agrotechnical practices and developing resistant varieties and hybrids through breeding and genetic techniques. Agrotechnical practices include selecting the appropriate sowing date to avoid exposing plants to low temperatures, choosing recommended varieties for the cultivation zone, removing early flowering plants, and using chemical treatments on seeds and vegetative plants (I.A. Oksenenko et al., 1987; K.S. Devlikamov et al., 2016; M. Sadeghi-Shoae et al., 2017). Breeding methods involve creating an analytical framework for the negative selection of flowering material. This includes practices such as ultra-early and sub-winter sowing, selection under long-day conditions, sowing with vernalized seeds, and sowing in soil treated with herbicides (A.V. Kornienko et al., 1983; A.V. Logvinov et al., 2021, 2022). It is crucial to assess genetic collections from global repositories of cultivated and wild accessions in order to identify new sources of resistance to flowering (E.S. Kutnyakhova et al., 2016; V.I. Burenin et al., 2018). An important method for generating new non-flowering alleles is mutagenesis using ethyl methanesulfonate. Markers for allelic variants (haplotypes) of functional flowering genes, as well as quantitative trait loci and single-nucleotide polymorphisms associated with resistance to bolting can be used in marker-assissted selection (B. Büttner et al., 2010; Y. Kuroda et al., 2019; S. Ravi et al., 2021). Great prospects for accelerated sugar beet selection and seed production can be achieved through the “seed to seed” scheme. This involves stimulation of bolting under artificial climate conditions by carefully controlled growing parameters, including the vernalization stage. Important parameters for successful vernalization are temperature, the phenophase of vernalization initiation, and the duration of the photoperiod.