Genetic analysis of bolting after winter in sugar beet (Beta vulgaris L.)

Abstract

This study reveals for the first time a major QTL for post-winter bolting resistance in sugar beet ( Beta vulgaris L.). The knowledge of this QTL is a major contribution towards the development of a winter sugar beet with controlled bolting behavior. In cool temperate climates, sugar beets are currently grown as a spring crop. They are sown in spring and harvested in autumn. Growing sugar beet as a winter crop with an extended vegetation period fails due to bolting after winter. Bolting after winter might be controlled by accumulating genes for post-winter bolting resistance. Previously, we had observed in field experiments a low post-winter bolting rate of 0.5 for sugar beet accession BETA 1773. This accession was crossed with a biennial sugar beet with regular bolting behavior to develop a F3 mapping population. The population was grown in the greenhouse, exposed to artificial cold treatment for 16 weeks and transplanted to the field. Bolting was recorded twice a week from May until October. Post-winter bolting behavior was assessed by two different factors, bolting delay (determined as days to bolt after cold treatment) and post-winter bolting resistance (bolting rate after winter). For days to bolt, means of F3 families ranged from 25 to 164 days while for bolting rate F3 families ranged from 0 to 1. For each factor one QTL explaining about 65% of the phenotypic variation was mapped to the same region on linkage group 9 with a partially recessive allele increasing bolting delay and post-winter bolting resistance. The results are discussed in relation to the potential use of marker-assisted breeding of winter sugar beets with controlled bolting.

A Detailed Analysis of the BR1 Locus Suggests a New Mechanism for Bolting after Winter in Sugar Beet (Beta vulgaris L.)

“…According to Pfeiffer et al (2014), a F 2 population consisting of 410 plants was derived from a single F 1 plant that was produced by a hand-cross of the biennial sugar beets BETA 1773 and 93161P (Figure S1). Seeds of BETA 1773 and 93161P were provided by the Leibniz Institute of Plant Genetics and Crop Plant Research, IPK (Gatersleben, Germany) and the breeding company Saatzucht Dieckmann (Nienstädt, Germany), respectively.…”

“…For a mapping-by-sequencing analysis, pools of 26 bolting-resistant and 297 bolting F 2 plants were used. Thereby, a single continuous homozygous region of 103 kb was co-localized to the previously published BR 1 QTL for post-winter bolting resistance (Pfeiffer et al, 2014). The BR 1 locus was narrowed down to 11 candidate genes from which a homolog of the Arabidopsis CLEAVAGE AND POLYADENYLATION SPECIFICITY FACTOR 73-I ( CPSF73-I ) was identified as the most promising candidate.…”

“…Kirchhoff et al (2012) identified beet accessions with low bolting tendencies (e.g., BETA 1773) after growing wild and cultivated beet accessions over winter. Recently, a major quantitative trait locus (QTL) for post-winter bolting resistance ( BR 1 ) was determined using a F 3 mapping population derived from a cross between BETA 1773 and a sugar beet which is regularly bolting after winter (Pfeiffer et al, 2014). Both parents were homozygous for the biennial btc1 allele and the annual BBX19 allele.…”

“…The QTL was mapped to chromosome 9 with a confidence interval of 4 cM and explained 65% of the phenotypic variation. Thereby, the BETA 1773 allele caused a reduced bolting rate in a partially recessive manner (Pfeiffer et al, 2014). F 3 families that were homozygous for the BETA 1773 allele at the BR 1 locus showed an average bolting rate of 0.33, indicating an incomplete penetrance of the bolting resistance allele.…”

“…To achieve this, we used the same F 2 population that was developed to genetically map the BR 1 QTL (Pfeiffer et al, 2014). This population segregated for bolting behavior after cold-treatment.…”