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 quantitative
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.