Genetic identification of a novel bolting locus in Beta vulgaris which promotes annuality independently of the bolting gene B Salah F. Abou-Elwafa • Bianca Bu ¨ ttner • Friedrich J. Kopisch-Obuch • Christian Jung • Andreas E. Mu ¨ ller Received: 15 February 2011 / Accepted: 9 November 2011 Ó Springer Science+Business Media B.V. 2011 Abstract Bolting tendency in the crop species Beta vulgaris, which includes sugar beet, is a complex trait governed by various environmental cues, including prolonged periods of cold temperatures over winter (vernalization) and photoperiod, and multiple genetic factors. Two loci which promote bolting in the absence of vernalization are known in beet, the major bolting locus B on chromosome II and the B2 locus on chromosome IX. Here, genetic linkage and quantita- tive trait locus analyses in two populations derived from a cross between a biennial genotype, which was identified in a phenotypic screen for EMS-induced bolting mutants and requires vernalization to bolt, and an annual wild beet accession revealed the presence of a novel major bolting locus B4 which is linked to the B locus but promotes annual bolting independently of B. The genetic distance between B and B4 on chromosome II is 11 cM. A sequence-based marker was identified which co-segregates with bolting behavior and co-localizes with the B4 locus. Keywords Sugar beet Á B4 locus Á Bolting Á Vernalization requirement Á Bienniality Introduction Sugar beet (Beta vulgaris L. ssp. vulgaris) is a biennial crop and requires prolonged exposure to low temper- atures between 2 and 10°C (vernalization) followed by long-day conditions for bolting (stem elongation) and flowering to occur (Lexander 1980). The promotive effect of these environmental cues on bolting in sugar beet was termed ‘photothermal induction’ (Owen et al. 1940), and, to some extent at least, low temperature and long daylength conditions can compensate for each other (Margara 1960; Van Dijk et al. 1997). Under non- inductive conditions such as short days or rapid exposure to warm ambient temperatures after vernal- ization, the inductive effect of vernalization is abol- ished and the plants revert to vegetative growth, a phenomenon known as devernalization (Lexander 1980). However, Fife and Price (1953) reported that bolting and flowering might also be induced under other environmental conditions such as prolonged cold treatment or continuous darkness. The authors sug- gested that light is not required for bolting initiation but is required for rapid development of bolters after stem elongation was initiated, which can occur after a long period of thermal induction regardless of daylength. For short-day conditions, Mutasa-Go ¨ttgens et al. (2010) reported that application of gibberellin growth Electronic supplementary material The online version of this article (doi:10.1007/s11032-011-9671-x) contains supplementary material, which is available to authorized users. S. F. Abou-Elwafa Á B. Bu ¨ttner Á F. J. Kopisch-Obuch Á C. Jung Á A. E. Mu ¨ller (&) Plant Breeding Institute, Christian-Albrechts-University of Kiel, Olshausenstr. 40, 24098 Kiel, Germany e-mail: a.mueller@plantbreeding.uni-kiel.de 123 Mol Breeding DOI 10.1007/s11032-011-9671-x