Biomedical Engineering Reference
In-Depth Information
Incorporation of water content measures demonstrated genetic variability for water
content, and that commercial hybrids tested have a slightly, but statistically signif-
icant, lower water content than USDA-ARS germplasm (McGrath unpublished).
Interestingly, the majority of putative QTLs for both sucrose content and sucrose
yield appear to co-segregate with QTLs for water content and/or water yield
[
57
]. By definition, the proportion of sucrose reflected in dry matter (e.g., dry
matter
¼
¼
water content) is also heritable, and breeding for dry matter
content will be a primary consideration for energy beets. Fortunately, sucrose
content and total dry matter are highly correlated in sugar beet [
46
].
Sucrose and betalains accumulate in vacuoles of parenchyma cells located in
between concentric cortical vascular rings that are a unique and distinguishing
feature of beets [
58
,
59
]. Accumulation and storage of biochemicals to economic
levels is currently limited to sucrose, glycine betaine, and betalain pigments, but
sucrose esters, fructans, specialty lipids, ascorbate, vanillin, and others theoretically
could be produced in beets [
8
,
60
,
61
]. Glycine betaine is an osmoprotectant and
feed additive. It is recovered from molasses during the removal of residual sucrose
[
62
,
63
]. Fresh beet products are good dietary sources of potassium and folic acid,
betalain pigments are considered antioxidants [
64
,
65
], and betaine has benefits to
human health mostly due to its role as an osmolyte and methyl donor [
66
]. Betalains
are used commercially as food colorings [
67
,
68
], and breeding for increased dye
concentrations shows that the quantity of betalain synthesized in the beet root is
under genetic control [
69
]. Protein concentrations are generally low in storage
roots, and assuming an adequate protein expression system in beets could be
developed, recovery of high-value bio-ceuticals could be facilitated.
Disease management is critical for beets, and recent reviews reinforce the need
for adequate levels of genetic resistance or tolerance to a range of biotic and abiotic
stressors [
1
,
3
,
30
]. As well, early season growth (e.g., the first 8-10 weeks) is a
critical phase for obtaining good field stands as well as for developing metabolic
capacity for biomass accumulation. A phase change from embryonic/juvenile
growth to adult vegetative growth coincides with an increased growth rate, accom-
panied by warming temperatures [
54
,
70
]. Sugar beets are normally planted into
cool (10-15
C, optimal germination is 20-25
C) soils to reduce the impact of
seedling diseases. Acquisition of disease tolerance from acute seedling diseases to
chronic root rot symptoms also occurs concomitantly with the juvenile to adult root
growth phase change.
biomass
1
Breeding Strategies and Integration of New Biotechnologies
Interest in sugar beet for biofuel production has renewed in recent years [
5
,
16
,
71
]. Briefly, the state of the art is the deployment of the highest quality seed made
from hybrids with highest demonstrated performance in each particular market.
Hybrids have evolved from 3- and 4-way combinations from the 1960 and 1970s,
through triploid hybrids from the 1970 to 1990s that exhibited performance gains
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