Download Genetic Improvement of Sweet Sorghum for the production of

Genetic Improvement of Sweet
Sorghum for the production of
Biofuels & Chemicals in Florida
• Terry Felderhoff
•
•
UF Genetics and Genomics Graduate Program
Sanyukta Shukla, Alejandra Abril, & Wilfred Vermerris
Why sweet sorghum is attractive for Florida
• Tall, annual, seep propagated crop
– Annual crop offers flexibility to the producer
– High solubile sugars in juice (~18%)
• Stress tolerant (drought, flood, heat) and limited
input requirements compared to sugarcane
• Opportunity to cultivate on marginal land
– Abandoned citrus groves
– Former tobacco land
• Minimal competition with food production
• Compatible with sugarcane production in South
Florida
Next-generation sweet sorghums: Sustainable production of
fuels and chemicals from juice and bagasse
fermentation
CO2
fuels
pentoses
hexoses
fermentation
chemicals (e.g. D-and L-lactate)
pretreatment
Sweet sorghum
chemicals
fuels
chemicals
lignin
nanotubes
United States Department of Agriculture
heat
enhanced
plastics
Sweet sorghum is a new crop in Florida
• Commercial sorghum breeding programs are mostly
based in Texas, Kansas and Nebraska
• Primary focus has been on grain and forage sorghums
• Mediocre performance of commercial sorghum in Florida
– Heavy pests and disease pressure
– Low water retention capacity of sandy soils
– Restrictions on the volume of irrigation water
• The UF sorghum breeding program is focusing on
developing regionally adapted sweet sorghums that give
high yields with limited inputs
Sweet sorghum cultivars
• Sorghum makes a single
reproductive structure
(panicle) and is a naturally
self-pollinating species
• Cultivars are pure lines
(inbreds) that can be
propagated via self-pollination
• Cultivars are ‘easy’ to develop
Cultivar breeding strategy: Pedigree method
Parents: high-sugar x other trait
400 F2 plants
Each year we evaluate 10-20 sweet
sorghums from around the world
F2: select 5-20 biggest and cleanest
plants
5-20 F3 families
F3: select 5-10 individuals among
and within families for biomass,
maturity, disease resistance
5-10 F4 families
F4: as F3 plus select for sugar
based on destructive sampling of
sibs
1-5 F5 families
F5: estimate sugar yield; compare
performance against checks; look
for homogeneity; bulk seed
1-3 F6 families
F6: replicated yield trials
(two years, three locations)
Release top performers
Sweet sorghum breeding targets
• High sugar yields
• Disease resistance
• Insect resistance
• High biomass yields
• Water use efficiency
• Bagasse amenable to processing
• Use marker-assisted selection for
complex traits to expedite line
development
Anthracnose
• Omnipresent in the
southeastern USA
• Resistance not
common in commercial
germplasm developed
in central USA
Mapping anthracnose resistance
Bk7
EH
X
135 F5 lines
Phenotyping
Genotyping
-
-
Field trials
Disease score
GBS (Cornell University)
5,186 SNPs
Genetic mapping of resistance
• Chromosome 7
– 45.2 Mb
• Chromosome 9
– 3.2 Mb
• Identified in UF
developed
cultivars
Sweet sorghum cultivars
Location
Sugar
Fresh stalk weight
Genotype
F4(Honey*BK7)-45-3-1
Gusher
6.7a
84.4a
F4(Mer 81-4 x BK7)-28-4-1
Caramelo
6.8a
67.7bc
F4(Mer 81-4 x BK7)-20-2-1
Fortuna
6.6a
73.4ab
F4(Mer 81-4 x BK7)-15-2-1
F4(Mer 81-4 x BK7)-1-2-1
Sweet Florida
Candycane
6.8a
72.0ab
7.2a
76.6ab
5.3b
60.0c
M81E
Commercial
(t/ha)
(t/ha)
Dry weight yields:
15-20 t/ha
Improved UF cultivars
Brown midrib sorghum
• Generated in the 70’s at Purdue University via chemical
mutagenesis – 19 recessive mutants
• Nine spontaneous bmr mutants discovered later on
• Initially used as forage because of improved intake and
palatability
Klason lignin (Purdue)
25
Klason lignin (mg/g )
20
15
Wt
bmr
10
5
0
N-bmr 2
N-bmr 3
N6-bmr
N-bmr 12
N-bmr 19
Wt-bmr isolines
The bmr mutations reduce lignin content by ~15-20%
Saballos et al. (2008) Bioenerg. Res. 1: 198
Enzymatic saccharification of bagasse (Purdue)
Pretreated
Unpretreated
(dilute sulfuric acid)
Glucose yields of sorghum stover from bmr and wild-type lines without and
with pretreatment after 48 h of enzymatic saccharification (60 FPU/g cellulose)
Saballos et al. (2008) Bioenerg. Res. 1: 198
Sweet sorghum hybrids
• Hybrids are the product of a cross between two different inbred
parents; the progeny is planted and harvested
• Benefits of hybrids:
– Potential for superior yield
– Seed production is combine-compatible (maybe….)
• Challenge 1: Since sorghum is a self-pollinating species, you
need a male-sterile female ‘A-line’ to ensure cross-pollination
• Challenge 2: The only way to propagate the A-line is to cross it
with a fertile B-line that is otherwise genetically identical
• Challenge 3: In order to get fertile hybrid seed (necessary for
sugar accumulation!), a male, fertility-restoring ‘R-line’ needs to
be available
A
B
R
Seed
Parent
Maintainer
Pollinator
Sanyukta Shukla
Combine-compatible hybrid seed production
• If we select the parents
carefully, we can get tall
offspring from short,
parent lines
• Four recessive,
independent dwarf genes
• Both hybrid parents need
to be sweet in order to
produce sweet offspring
• But is height a
prerequisite for being
sweet?
Tall sorghums tend to be sweeter…..
Brix as a function of plant height
20
18
But….
16
14
Brix
12
10
8
6
y = 0.017x + 8.4817
R² = 0.222
4
2
0
0
50
100
150
200
250
300
350
400
Plant height (cm)
Data based on 250 F3 families derived from grain x sweet sorghum
Ana Saballos and Sanyukta Shukla
Short Sweet Sorghum
• Tall sorghums tend to be sweeter than short sorghums, but
short sorghums can be sweet
– Height is not a prerequisite in sweet sorghums
• Good news: It is possible to produce short sweet inbred
parents for hybrid sweet sorghums
• Short, sweet inbred parents for hybrid production under
development:
– 22 R-lines
– 73 B-lines (being converted to A-lines)
Sanyukta Shukla
dw1 dw2 Dw3 Dw4
Dw1 Dw2 dw3 dw4
Dw1 Dw2 Dw3 Dw4
Conclusions
• Sweet sorghum is an excellent bioenergy crop
for Florida
• The great genetic diversity within sorghum can
be exploited to develop improved, regionally
adapted bioenergy sorghums
– Cultivars developed at UF outperform other
sorghum cultivars
• Short sweet sorghums can be developed for tall
hybrid sweet sorghum production
Dr. Ana Saballos
Dr. Lonnie Ingram
Amelia Dempere
Dr. Julene Tong
Randy Powell
Maury Radin
Jared Lindey
Steven Smith
Dr. John Erickson
Dr. Jim Preston
Dr. KT Shanmugam
Dr. Brad Krohn
Dr. Wilfred Vermerris
[email protected]
United States Department of Agriculture