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1. Alleles of GWD, PWD and SEX4 have been identified in a wide
collection of potato genotypes
2. These same genotypes have been characterized for P content
3. Alleles correlating with high or low P content have been
identified
4. Epistatic effects of starch phosphorylation are being analysed
(specially effect of reduced P on yield)
5. Positive and strong alleles will be introgressed in potato elite
lines
Bioresource (PBR 31306)
Tailoring of potato starch (GM)
Bioresource (PBR 31306)
E. coli
Branching
enzyme (GlgB)
Streptococcus downei
Mutansucrase gtfi
Human - Laforin
CBM25
A. thaliana
Water dikinase
Bacterial Glucansucrases
L. mesenteroides
Dextransucrase
dsrs
L. mesenteroides
Alternansucrase asr
Expression of different heterologous proteins lead to changes in starch granule morphology and properties of starch
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Sugarbeet
Crop characteristics:
● Cross pollinator
● Most commonly diploid and tetraploid
● Originally self-incompatible
● Root has high sucrose (sugar) content
Bioresource (PBR 31306)
Sugar content in sugar beet
History:
● Modern sugarbeets are originated from selections made in the
middle of the 18th century from fodderbeets grown in then
German Silesia
● Breeding of sugarbeet was intensified during the blockade of
shipments of cane sugar to Europe by the British during the
Napoleonic wars
● The sugar extraction process developed in the 19th century has
created a market for sugarbeet and thus breeding of this crop
enforced
Bioresource (PBR 31306)
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Breeding sugarbeet
Breeding of the first varieties of sugar beet ware done by mass selection
These varieties were followed by better ones produced by anisoploid (triploid) synthetic varieties resulting from crossing diploid and tetraploid lines
Diploid male sterile x tetraploid pollinators
Current sugarbeet varieties are diploid hybrids
1. Making diploid inbred parents containing the required traits
(sugar content, resistance to pathogens, and sugar quality)
2. making hybrid seeds
Bioresource (PBR 31306)
Synthetic: refers to varieties that result from crossing of multiple (>2) parents
Breeding sugarbeet
Breeding targets:
● Total root yield
● Sucrose yield
● More recently breeding
for sugar quality has
become a target.
Current yield in The Netherlands:
● Average root yield ~ 60 tons/ha
● Average sugar yield ~ 10 tons/ha (16%)
Bioresource (PBR 31306)
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Sugarcane
Perennial grass
Comprises 6 species but Saccharum
officinarum is the major contributor of
high sucrose in modern varieties
Genetics: 2n=80 chromosomes
Contains a lot of duplications and
unpaired chromosomes
Breeding is a great challenge!!
Breeding targets:
● Sugar yield!
● Ratooning performance, resistance to pathogens, low fibre, cane yield.
Bioresource (PBR 31306) Further reading: Jackson. 2005. 92: 277290
Breeding sugarcane
Breeding of sugarcane happen in three phases:
1. Crossing and selecting among S. officinarum clones: these
varieties had high sugar content and low fibre content, but
they were susceptible to diseases and lacked vigour
2. Development of interspecific hybrids between S. officinarum
and other species (mostly S. spontaneum): these were
vigorous and with good ratooning performance but they had
lower sucrose levels. By backcrossing the hybrids with S.
officinarum rubust high-sugar-high-yielding varieties were
generated: “wonder cane” (ancestry of all modern varieties)
3. Exploitation of interspecific hybrids from phase 2 by recurrent
selection
Bioresource (PBR 31306)
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Breeding sugarcane
Most modern varieties are made from a small number of original progenitors
Narrow genetic basis of sugarcane breeding programs
Limited possibilities for introgression or improvement of new traits
Bioresource (PBR 31306)
Breeding sugarcane
Bioresource (PBR 31306)
Sugar yield/ha has increased
But...that was not to increase in sugar content but due to improvements in total biomass yield
Future:
● Increase genetic basis in
breeding programs
● Developing genetic markers
for different positive and
negative traits
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Fructans in plants
Fructans are the major form of storage carbohydrates in grasses:
● Are important to sustain regrowth of the plant after defoliation
● Nutritive value of feed
● When extracted can be used as sweeteners as humans are not
able to degrade fructans
Bioresource (PBR 31306)
Breeding fructans in wheat
Genetic markers (QTL’s) for fructan yield in wheat grain have been
(recently) identified
Breeding strategy: Marker
Assisted Selection (MAS)
Identify the genes underneath
these QTL’s would create tools
for breeding in other crops
Bioresource (PBR 31306)
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Summary
Starch, sucrose and fructans are the main storage forms of “easily
degradable” sugars and they are specific to each crop.
Each crops has different characteristics and different
genetic/breeding tools are available – this determines breeding
strategy
Breeding for sugar/starch content is often indirect. The real target is
crop yield
Starch biosynthetic pathway is well characterized and starch quality
has been mainly tackled using candidate gene approaches both GM
and non-GM.
Breeding of polyploids (potato and sugarcane) is much more difficult
than diploids species
One (future) line of potato breeding is through diploids