Breeding Methods in CrossPollinated Crops

1

• Breeding Methods in Cross-Pollinated Crops
• Mass Selection
• Recurrent Selection
• Reciprocal Recurrent Selection
• Synthetic cultivars
• Hybrid cultivars
• Review fertility regulation
• incompatibility
• gametophytic
• sporophytic
• male sterility
• genetic
• cytoplasmic (may not exist??)
• genetic-cytoplasmic

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Breeding Methods in Cross-Pollinated Crops Review
fertility regulation Incompatibility 1. form
of infertility a. normal gametic production,
male and female b. physiological hindrance to
fertilization i. failure of pollen tube to
penetrate the stigma ii. failure of pollen
tube to grow normally may not grow full
length may grow so slowly that ovule
looses viability 2. restricts
selfing/inbreeding and encourages
crossing/outbreeding
3

• Breeding Methods in Cross-Pollinated Crops
• Review fertility regulation
• incompatibility
• gametophytic (ex. found in clovers, grasses, and
  potatoes)
• controlled by a series of alleles at 1 or more
  loci, usually designed S1, S2, etc.
• RECALL that the pollen is haploid and the stylar
  tissue is diploid
• SUCH THAT if the allele in the pollen is
  identical to either of the alleles in the style
  of the female plant then the two genotypes are
  incompatible

4

• Breeding Methods in Cross-Pollinated Crops
• Review fertility regulation
• incompatibility with single gene

S1S2 x S1S2
S1S2 x S1S3
S1S2 x S3S4
S1 or S2
S1 or S3
S3 or S4
S1S2
S1S2
S1S2
Genotypes produced
no embryos S1S3 S1S3
S2S3 S1S4 S2S3 S2S4
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• Breeding Methods in Cross-Pollinated Crops
• Review fertility regulation
• incompatibility with 2 gene system
• Let incompatibility loci be designed as S and
  Z such that
• S1S2Z1Z2 x S1S2Z1Z2 incompatible
• S1S2Z1Z2 x S1S2Z1Z3 compatible in that
  pollen that is S1Z3 or S2Z3 will be
  functional
• According to Fehr, the 2 gene system results in
  about 10 more compatible matings than the 1
  gene systems

6

• Breeding Methods in Cross-Pollinated Crops
• Review fertility regulation
• Sporophytic incompatibility
• apparently a single gene system
• more complex because dominance is expressed by
  some alleles
• AND incompatibility is imparted to the pollen
  by the sporophyte or plant and not by the
  allelic make up of the gamete
• found in cabbage and brussel sprouts

7
Breeding Methods in Cross-Pollinated Crops Review
fertility regulation Incompatibility Tifhi hybrid
bahiagrass Developed by use of 2 clones that
are each self incompatible but are cross
compatible such that any seed set on either clone
has to be hybrid seed.
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• Breeding Methods in Cross-Pollinated Crops
• Review fertility regulation
• Male sterility
• cytoplasmic-genetic (cms)
• genetic
• recessive involves only nuclear genes
• Ms Ms or Ms ms male fertile
• ms ms male sterile
• Therefore it is impossible to have a pure line
  ms ms because you cant maintain, i.e. no pollen
  production
• Thus of limited value in hybrid production
  because you cant maintain one of the required
  inbreds in a homozygous state
• Greatest value is in eliminating emasculation
  in making crosses

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Breeding Methods in Cross-Pollinated Crops Review
fertility regulation Male sterility Genetic
male sterility ms ms x Ms Ms F1 Ms ms F2
.25 msms .5 Msms .25 MsMs What will the F3
look like if Self pollinating? Cross
pollinating?
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Breeding Methods in Cross-Pollinated Crops Review
fertility regulation Male sterility Genetic
male sterility ms ms x Ms Ms F1 Ms ms F2
.25 msms .5 Msms .25 MsMs What will the F3
look like if Self pollinating? .25 msms sterile
F2 contribute no progeny and Therefore genotypic
freq. of Msms .67 and MsMs .33 Msms
(.25)(.67) msms (.50)(.67) Msms (.25)(.67)
MsMs .33 MsMs F3
.1675 ms ms .335 Ms ms .4975
Ms Ms
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Breeding Methods in Cross-Pollinated Crops Review
fertility regulation Male sterility Genetic
male sterility ms ms x Ms Ms F1 Ms ms F2
.25 msms .5 Msms .25 MsMs What will the F3
look like if Self pollinating? .25 msms sterile
so contributes nothing to next generation Therefor
e genotypic freq. of Msms .67 and MsMs
.33 Msms (.25)(.67) msms (.50)(.67) Msms
(.25)(.67) MsMs .33
MsMs F3 .1675 ms ms .335 Ms ms
.4975 Ms Ms
Continue to increase the freq. of the homozygous
male fertile genotype, i.e. loose the male
sterile allele
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Breeding Methods in Cross-Pollinated Crops Review
fertility regulation Male sterility Genetic
male sterility ms ms x Ms Ms F1 Ms ms F2
.25 msms .5 Msms .25 MsMs What will the F3
look like if Cross pollinating? New allelic
freq.(ms) .5/.75 .33 pm (NOTE reverse
order) freq.(Ms) (.5)(.5)(.25)/.75.67
(1- pm) Why pm and 1-pm????
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Breeding Methods in Cross-Pollinated
Crops Genetic male sterility F2 .25 msms
.5 Msms .25 MsMs What will the F3 look like
if Cross pollinating? New allelic freq.(ms)
(.5)(.5)/.75 .33 pm (Note reverse
order) freq.(Ms) (.5)(.5)(.25)/.75.67
(1- pm) Thus the next generation will have the
following genotypic freq. pmpf pm(1-pf)
pf(1-pm) (1-pm)(1-pf) (.33)(.5)msms
(.33)(.5) (.5)(.67)Msms (.67)(.5) MsMs
0.165 msms .5 Msms .335 MsMs New allelic
freq. of ms in fertile plants (.5)(.5) / .835
.299 pm
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Breeding Methods in Cross-Pollinated
Crops Genetic male sterility F2 .25 msms
.5 Msms .25 MsMs What will the F3 look like
if Cross pollinating? New allelic freq.(ms)
(.5)(.5)/.75 .33 pm (Note reverse
order) freq.(Ms) (.5)(.5)(.25)/.75.67
(1- pm) Thus the next generation will have the
following genotypic freq. pmpf pm(1-pf)
pf(1-pm) (1-pm)(1-pf) (.33)(.5)msms
(.33)(.5) (.5)(.67)Msms (.67)(.5) MsMs
0.165 msms .5 Msms .335 MsMs New allelic
freq. of ms (.5)(.5) / .835 .299 pm
inc. freq of the Ms allele
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Breeding Methods in Cross-Pollinated
Crops Genetic male sterility F2 .25 msms
.5 Msms .25 MsMs What will the F3 look like
if Cross pollinating? New allelic freq.(ms)
(.5)(.5)/.75 .33 pm (Note reverse
order) freq.(Ms) (.5)(.5)(.25)/.75.67
(1- pm) Thus the next generation will have the
following genotypic freq. pmpf pm(1-pf)
pf(1-pm) (1-pm)(1-pf) (.33)(.5)msms
(.33)(.5) (.5)(.67)Msms (.67)(.5) MsMs
0.165 msms .5 Msms .335 MsMs New allelic
freq. of ms (.5)(.5) / .835 .299 pm
inc. freq of the Ms allele
dec. freq. of the ms allele which will eventually
be lost from population
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• Breeding Methods in Cross-Pollinated Crops
• Review fertility regulation
• Male sterility
• genetic
• cytoplasmic-genetic
• Discovered by Quinby and Stevens in sorghum at
  Chillicothe, TX
• Milo (durra) x Kafir
• F1 all fertile
• F2 segregated to 3 fertile and 1 male
  sterile
• How could this happen?
• need a cytoplasmic factor (S (sterile) or N
  (normal))and a nuclear gene (F (fertility
  restoring) and f (non fertility restoring))that
  will over ride the cytoplasmic factor

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Breeding Methods in Cross-Pollinated
Crops genetic-cytoplasmic male sterility Such
that Durra is S-FF Kafir is
N-ff F1 S-Ff (all fertile) F2 .25
Sff .50 S-Ff .25 S-FF
¼ sterile ¾ fertile What
would have been the results had the cross been
made in the opposite direction, i.e. kafir x
durra?
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Breeding Methods in Cross-Pollinated
Crops genetic-cytoplasmic male sterility All
genetic-cytoplasmic male sterility systems work
in this manner and provide breeders with the
opportunity to develop male sterile lines
(A-lines) that can be maintained by near
isogenetic lines (B-lines) and lines that serve
as the other inbred line in the hybrid that will
restore fertility in the hybrid (call R-lines),
i.e. A-line male sterile, produces no pollen
maintained by crossing with B-line serves as
the female line in hybrid production B-line male
fertile via Normal cytoplasm used only to
reproduce more A-line plants can be selfed to
replenish seed supply R-line male fertile by
virtue of fertility restoration gene
(homozygous by virtue of being inbred) may
carry either S or N cytoplasm serves as the
male line in hybrid production
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Breeding Methods in Cross-Pollinated
Crops genetic-cytoplasmic male sterility SUCH
THAT A-line x R-line F1 hybrid (male
fertile) S-ff x N-FF S-Ff Maintenance of
the A-line is with the B-line SUCH THAT A-line x
B-line A-line S-ff x N-ff S-ff (male
sterile A-line)
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Breeding Methods in Cross-Pollinated
Crops genetic-cytoplasmic male sterility Male
sterility can be introduced into any fertile line
simply by using any existing A-line, e.g. A-line
x WS1 (which is fully fertile via cytoplasm and
restorer genes) S-ff x N-FF F1 S-Ff x WS1
(N-FF) BC1F1 5050 S-Ff and S-FF (progeny
test to next gen.) BC1F2 .125 S-ff .25
S-Ff .625 S-FF identify male sterile
and BC to WS1 Repeat BC cycle A simple backcross
of WS1 to the B-line for my A-line above will
produce the WS1 (N-ff) B line for maintenance
of WS1 A-line
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Breeding Methods in Cross-Pollinated
Crops genetic-cytoplasmic male sterility Male
sterility can be introduced into any fertile line
simply by using any existing A-line, e.g. A-line
x WS1 (which is fully fertile via cytoplasm and
restorer genes) Obvious in the previous scenario
that WS1 is an R-line but I could take any B-line
and convert it to an R-line, e.g. WS A-line x any
R-line S-ff x N-FF
S-Ff .25 S-ff .5 S-Ff .25 S-FF
22
Breeding Methods in Cross-Pollinated
Crops genetic-cytoplasmic male sterility Male
sterility can be introduced into any fertile line
simply by using any existing A-line, e.g. A-line
x WS1 (which is fully fertile via cytoplasm and
restorer genes) Obvious in the previous scenario
that WS1 is an R-line but I could take any B-line
and convert it to an R-line, e.g. WS A-line x any
R-line backcross to WS-A-line S-ff
x N-FF S-Ff Repeat to BCnF2 and
then self .25 S-ff .5 S-Ff .25 S-FF to find
the .25 S-FF (recall that the cytoplasm
in the R-line is irrelevant
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Breeding Methods in Cross-Pollinated
Crops genetic-cytoplasmic male sterility A, B,
and R-lines are not normally derived by
conversion Breeders will work with a population
to develop a set of inbred lines cross a
developed inbred with an A-line tester if
progeny sterile, what was the make up of the
derived inbred had to be N-ff (otherwise would
already know it was sterile) THUS this
derived line will be worked with as an
A-line if the progeny are fertile had to be
N-FF or S-FF and will be worked with as an R-line
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• Breeding Methods in Cross-Pollinated Crops
• Mass Selection
• Recurrent Selection
• Reciprocal Recurrent Selection
• Synthetic cultivars
• Hybrid cultivars
• We have considered combining ability, population
  improvement, and fertility regulation.
• Now consider types of hybrids
• varietal hybrids (i.e., non inbred parents)
• single crosses
• double crosses
• modified single
• modified double
• 3-way
• and a partridge in a pear tree

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• Breeding Methods in Cross-Pollinated Crops
• Hybrid cultivars
• Consider 1000 inbred lines and their evaluation
• 1000 x (a single tester) 1000 hybrids to
  evaluate
• 1000 x 2 testers 2000 hybrids to evaluate,
  etc.
• Consider the possible unique single cross
  hybrids from 20 inbreds
• Function of the possible unique combinations of
  n inbreds such that
• C(n,r) n! / r!(n-r)!
• i.e., the combination of n things taken r at
  a time
• or, the combination of 20 inbreds taken 2 at
  a time
• C(n,r) n! / r!(n-r)! 20! / 2! (20-2)!
• (20) (19)(18!) / (2)(1)(18!)
  (20)(19)/(2)(1) 190

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• Breeding Methods in Cross-Pollinated Crops
• Hybrid cultivars
• Consider the possible unique 3-way cross hybrids
  from 20 inbreds
• C(n,r) n! / r!(n-r)!
• i.e., the combination of n things taken r at
  a time
• or, the combination of 20 inbreds taken 3 at
  a time
• C(n,r) n! / r!(n-r)! 20! / 3! (20-3)!
• (20) (19)(18)(17!) / (3)(2)(1)(17!)
• (20)(19)(18) / (3)(2)(1)
• 6,840 / 6 1140
• Unique without rearrangement or reciprocal such
  that
• (A x B) x C unique and equals (A x C) x B and (B
  x C) x A

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• Breeding Methods in Cross-Pollinated Crops
• Hybrid cultivars
• Consider the possible unique 4-way cross hybrids
  from 20 inbreds
• C(n,r) n! / r!(n-r)!
• i.e., the combination of n things taken r at
  a time
• or, the combination of 20 inbreds taken 4 at
  a time
• C(n,r) n! / r!(n-r)! 20! / 4! (20-4)!
• (20) (19)(18)(17)(16!) / (4)(3)(2)(1)(16!)
• (20)(19)(18)(17) / (4)(3)(2)(1)
• 116280 / 24 4845
• Unique without rearrangement or reciprocal such
  that
• (AB) x (CD) unique and equals (AC)(BD) and
  (AD)(BC)

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Potential double cross combinations Empirical
proof 6 inbreds 1 2 3 4 5
6 12/34 13/24 14/23 12/35 13/25 15/23 12/36 12/45
12/46 12/56 13/45 13/46 13/56 14/56 23/45 23/46 2
3/56 24/56 34/56 35/46 36/45 Total 45
C(n,r) n! / r!(n-r)! C(6,4) 6! / 4!(6-4)!
(6)(5)(4)(3)(2!) / (4)(3)(2)(1)(2!) 360/24
15 However, since each double cross can be
rearranged to 3 non reciprocal combinations, the
total hybrids with rearrangement is 45
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• Breeding Methods in Cross-Pollinated Crops
• Hybrid cultivars
• Consider the number of possible hybrids
• w/o rearrangement with rearrangement
• single crosses (AB) 190 190
• 3-way crosses (AB)C 1,140 3,420
• double crosses (AB)(CD) 4,845
  14,535

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• Breeding Methods in Cross-Pollinated Crops
• Hybrid cultivars
• Performance of double cross and 3-way cross
  hybrids MAY be predicted by single cross
  averaging, e.g.
• for the double cross (A x B) x (C x D)
• performance may be predicted by
• ¼ (A x C) (A x D) (B x C) (B x D)
• etc.

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• Breeding Methods in Cross-Pollinated Crops
• Hybrid cultivars (Additional Comments)
• Early corn hybrids in the U.S. were double cross
  hybrids although scientists knew that single
  cross hybrids expressed greater heterosis and
  were higher yielding than double crosses
• Why?

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• Breeding Methods in Cross-Pollinated Crops
• Hybrid cultivars (Additional Comments)
• Today breeders use modified single cross OR a
  double modified single cross to increase the
  amount of seed harvested from the female rows.
• MSC (P1 x P1) x P2 DMSC (P1 x P1) x (P2 x
  P2)
• F1 seed to producer
• Pn and Pn are related, full or half sib lines,
  or otherwise closely related lines. NOTE that
  seed for sale is being harvested from a single
  cross F1 hybrid just as it was with corn and the
  use of double cross hybrids EXCEPT that the lines
  are related and therefore hybrid vigor and
  therefore seed production are reduced (although gt
  P1 alone)

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• Breeding Methods in Cross-Pollinated Crops
• Hybrid cultivars (Additional Comments)
• modified 3-way cross
• (P2 x P3) x (P1 x P1)
• F1 seed to producer
• Double cross
• (P1 x P2) x (P3 x P4)

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• Breeding Methods in Cross-Pollinated Crops
• Hybrid cultivars (Additional Comments)
• NOTE that the female parent or inbred may be male
  sterile OR as with corn today, male flowers are
  mechanically removed

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• Breeding Methods in Cross-Pollinated Crops
• Hybrid cultivars (Epilogue Environmental male
  sterility)
• In RICE there are two possible male sterility
  strategies
• cytoplasmic-genetic or A-B-R system previously
  described
• 2. 2-line system that uses photosensitive (pgms)
  or thermosensitive (tgms) genetic male sterility
  as the female and a non-sensitive lines as the
  male
• Ms Ms
• ms x Ms
• F1 hybrid

pgms fertile in short days and male sterile in
long days tgms fertile at low temps and male
sterile at high temperatures Theoretical ?????
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Breeding Methods in Cross-Pollinated Crops Hybrid
cultivars (Epilogue II Apomixis) Sexual clone
Sexual female x apomictic male
S1 F1 S2 (sexual) apomicts
apomicts F2 sexual S3 (sex)
apomicts apomicts F3
Obligate Apomictic lines ? New Cultivars
The sexual clone is heterozygous and so both
sexual and apomicts are found in the segregates.
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