Genetic analysis of sucrose accumulation in sugar beet (Beta vulgaris L.)

Genetic maps have been widely used to characterize important agronomic traits. The first objective of this research was to develop a sugar beet ( Beta vulgaris L.) genetic map for quantitative trait loci (QTL) analysis of root sucrose content using AFLP markers generated with both Eco RI/MseI and PstI/MseI restriction enzyme pair combinations. The genetic map was generated from a segregating population derived from an intraspecific cross between a sugar beet and a table beet line. The map showed a high density of markers on the n = 9 chromosomes of B. vulgaris. PstI/ MseI-derived AFLP markers presented lower proportions of clustering, of segregation distortion and a higher proportion of markers linked on linkage groups with respect to EcoRI/MseI-derived markers. PstI/MseI-derived AFLP markers were highly efficient in generating the genetic map. QTL analysis of the compounded trait root sucrose content expressed as percent of the fresh weight (% SucFW) was more efficiently analyzed considering the combination of root dry matter content (% DM) and sucrose content expressed as percent of the dry matter (% SucDM) separately. The second objective of this research was to analyze QTL locations for % DM and % SucDM in relation to % SucFW to understand the relative importance of these two traits to the final values of % SucFW. Traits were evaluated on field-grown F3 progeny-tests derived from the mapping population for two consecutive years. A total of seven QTL were detected for % SucFW, which all co-localized or with QTL for % DM (three) or with % SucDM (three) or with both (one), while six more QTL were only identified for % DM (one) and for % SucDM (five) but not identified for % SucFW. Overall, both DM and SucDM influenced SucFW and a total of 13 QTL appeared to control root sucrose content. The third objective of this research was to characterize the dynamics of sucrose accumulation and the changes in gene expression during early root development, and to identify genes differentially expressed between developmental phases characterized by different rates of sucrose accumulation. Sucrose accumulation dynamics were characterized in greenhouse- and field-grown plants for two consecutive years, and gene expression profiles were analyzed with cDNA-AFLP during early root development. (Abstract shortened by UMI.)...