Beta vulgaris L., sugarbeet, is an important plant for sucrose production in the U.S. and worldwide. One limitation for sugarbeet production is poor germination. Breeding for improved germination and seedling vigor has been unsuccessful due to low heritability of traits controlling germination vigor, few molecular markers and high environmental variability. Germination and seedling responses to stress in two beet varieties with differing vigor were studied in hydrogen peroxide and water. Differences in water absorption and internal hydrogen peroxide concentrations were observed between varieties. Gene expression changes were identified qualitatively (343 genes) and quantitatively (48 genes) during germination. In both varieties, germination was characterized by a rapid uptake of water and rapid gene activation within the first 24 h of imbibition. Upregulation of putative LTP4 (lipid transfer protein), MPK4 (MAP Kinase 4), BRI1 (Brassinosteroid 1), and MKK9 (MAPK Kinase 9) was associated with response to H2O2. The 48 genes, tested for expression in germination vigor, were evaluated for their ability to predict vigor in 3-week old seedlings of the same two varieties. Gene expression of seedlings treated with H2O, Aphanomyces sp., or Rhizopus sp. had different quantitative and temporal expression patterns depending on the variety and treatment. BRI1 and CAF1 (CCR4-NOT Associated Factor) were upregulated in both varieties in response to pathogen treatments. Of the 48 genes quantitatively tested between seeds and seedlings, varieties and the stress treatments, only BRI1, LTP4 and MKK9 were consistently upregulated. These genes may be useful as molecular markers for breeding efforts to enhance seedling vigor.
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