Breeding Methods in CrossPollinated Crops

1

• Breeding Methods in Cross-Pollinated Crops
• Mass Selection
• Recurrent Selection
• Reciprocal Recurrent Selection
• Synthetic Cultivars
• Hybrids

2

• Breeding Methods in Cross-Pollinated Crops
• Mass Selection
• Same form as with self-pollinated crops
• essentially a form of maternal selection since
  no pollination control
• select desirable plants
• bulk seed
• repeat cycle
• with strict selection breeder will reduce popul.
  Size
• slow genetic gain since lack pollination control
• must be able to ID superior phenotypes
• Not suitable for quantitative traits

3

• Breeding Methods in Cross-Pollinated Crops
• Mass Selection
• Recurrent Selection
• designed to increase the freq. of desirable
  genes within a population
• developed in the 1940s for developing inbred
  lines
• original corn inbreds came from OP varieties
• selection of new inbreds from these 1st
  generation hybrids did not result in improved
  2nd gen. hybrids
• so the theory evolved that the proportion of
  superior inbred lines depended on the proportion
  of superior alleles within the population
• so recurrent selection was devised to increase
  the frequencies of superior alleles

4

• Breeding Methods in Cross-Pollinated Crops
• Mass Selection
• Recurrent Selection
• Yr 1 self a number of plants
• select and harvest only superior plants at
  maturity (keep separate
• Yr 2 plant as progeny row nursery and allow to
  intermate thus re-establishing HWE
• Repeat cycle

5

• Breeding Methods in Cross-Pollinated Crops
• Mass Selection
• Recurrent Selection (Cycle 1)
• Year 1

x selfed x selected at maturity (superior
performing plant)
Year 2 Plant in an intercross block and allow
intermating to re-establish HWE


6

• Breeding Methods in Cross-Pollinated Crops
• Mass Selection
• Recurrent Selection (Cycle 2)
• Year 3

x selfed x selected at maturity (superior
performing plant)
Year 4 Plant in an intercross block and allow
intermating to re-establish HWE


7

• Breeding Methods in Cross-Pollinated Crops
• Mass Selection
• Recurrent Selection (Cycle n of continuing
  cycles)
• Year n

x selfed x selected to initiate inbred line
development MAY self and cross with a tester.


Year n1 Plant in an intercross block and allow
intermating to re-establish HWE AND performance
test hybrids
8

• Breeding Methods in Cross-Pollinated Crops
• Mass Selection
• Recurrent Selection
• Reciprocal Recurrent Selection
• Proposed by Comstock, Robinson, and Harvey
  (1949) to select for both general and specific
  combining ability
• General combining ability (GCA) is the ability
  of a breeding strain to combine favorably with
  many other strains or inbred lines. Analogous to
  ADDITIVE gene action
• Specific combining ability (SCA) is the ability
  of a genotype to combine favorably with one or a
  few other genotypes. Analogous to DOMINANT gene
  action

9
Yields for 45 single crosses (complete diallel
without selfs)
Which lines show GCA? SCA?
10

• Breeding Methods in Cross-Pollinated Crops
• Mass Selection
• Recurrent Selection
• Reciprocal Recurrent Selection General Outline
  for Improvement of Population A and Population B
• Yr. 1 Select individual plants before
  pollination in each popul.
• Self selected plants in each popul.
• Cross selected A plants to random B plants
• Cross selected B plants to random A plants
• Thus producing AB hybrids and BA hybrids
• Harvest selfed seed per plantplace in storage
• Harvest hybrid AB and BA seed and condition for
  planting

11

• Breeding Methods in Cross-Pollinated Crops
• Mass Selection
• Recurrent Selection
• Reciprocal Recurrent Selection General Outline
  for Improvement of Population A and Population B
• Yr. 2a. Plant AB hybrids in a performance trial
  (loc? reps?)
• Plant BA hybrids in a performance trial (loc?
  reps?)
• At maturity, harvest and determine superior AB
  and BA hybrids

12

• Breeding Methods in Cross-Pollinated Crops
• Mass Selection
• Recurrent Selection
• Reciprocal Recurrent Selection General Outline
  for Improvement of Population A and Population B
• Yr. 2b. Analyze data and determine the selfed A
  plants that produced superior AB hybrids and
  the selfed B plants that produced superior BA
  hybrids.
• Yr. 3. Retrieve selfed seed from storage and
  plant in an intermating nursery the A plants
  that produced superior AB hybrids to
  re-establish HWE
• Same for selfed B plants
• End first cycle of Reciprocal Recurrent Selection

13

• Breeding Methods in Cross-Pollinated Crops
• Mass Selection
• Recurrent Selection
• Reciprocal Recurrent Selection General Outline
  for Improvement of Population A and Population B
• NOTE Sometimes referred to as Reciprocal
  Half-sib Selection
• AND you can develop Reciprocal Full-sib Selection
  with cross pollinated species where you can
  produce both selfed and hybrid seed on the same
  plant (wheat, rice, corn lines that produce gt 1
  ear, grasses, others?) Hallauer, 1967 Lonnquist
  Williams, 1967

14
Average yield gains per cycle with different
intrapopulation recurrent selection schemes in
maize (adapted from Sprague and Eberhart, 1977)
15

• Breeding Methods in Cross-Pollinated Crops
• Mass Selection
• Recurrent Selection
• Reciprocal Recurrent Selection
• Although Recurrent and Reciprocal Recurrent
  Selection methods were originally designed and
  used to improve the chances of developing
  superior inbreds of corn, these procedures are
  not used in private industry for that purpose
  today.
• Most new inbreds in corn and sorghum are
  developed through pedigree or pedigree type
  procedures

16

• Breeding Methods in Cross-Pollinated Crops
• Mass Selection
• Recurrent Selection
• Reciprocal Recurrent Selection
• Synthetic cultivars
• First Generation Synthetic (Syn 1)
• Advanced Generation Synthetic

17

• Breeding Methods in Cross-Pollinated Crops
• Synthetic cultivars
• First Generation Synthetic (Syn 1)
• First generation progenies derived by
  intercrossing (polycross nursery) a specific
  set of seed-propagated lines or clones
• Usually used with cross pollinated crop spp.
• Can be used with self pollinated spp. if
  genetic (usually) mechanism have been
  introduced to maximize cross pollination,
  e.g. male sterility
• Limited to the 1st generation progeny and
  therefore can not be reproduced from seed of the
  1st generation.
• Examples include pearl millet, rye, alfalfa,
  turf grasses

18

• Breeding Methods in Cross-Pollinated Crops
• Synthetic cultivars
• First Generation Synthetic (Syn 1)
• Advanced Generation Synthetic
• Consist of seed harvested from successive
  generations beyond the 1st generation of a
  synthetic
• The Syn 2 is derived from the Syn 1 Syn 3 from
  Syn 2 ,etc
• Examples include grasses and forage crops
• Advanced generation synthetics are stable usually
  for a limited number of generations and then must
  be reconstituted.

19
Breeding Methods in Cross-Pollinated
Crops Synthetic cultivars (additional
comments) Once superior clones or lines are
identified then they can be mated in various
combinations. The performance of the Syn-2 MAY be
predicted from the performance of individual
clones/lines and the Syn-1 in the same way that
F2 performance can be predicted from manually
derived F1 hybrids. To predict the performance of
F2 populations (and thus syn-2 cultivars) in a
diploid spp. Wright (1922) proposed the following
formula Predicted F2 MF1 (MF1 MP) / n,
where F2 predicted performance of the F2
population (or synthetic 2) MF1 mean
performance of all possible single crosses of n
parents or mean of Syn1 performance MP
mean performance of all parents n number
of parents of each hybrid combination, e.g. 2 in
sc, 4 in double cross, etc. OR ALL CLONES
in a SYNTHETIC
20
Breeding Methods in Cross-Pollinated
Crops Synthetic cultivars (additional
comments) Or Predicted F2 or Predicted Syn2
MF1 (MF1 MP) / n number of clones
in original synthetic mean performance of
all clones mean performance of Syn 1
21

• Breeding Methods in Cross-Pollinated Crops
• Synthetic cultivars (additional comments)
• Performance of Synthetic cultivars (contid)
• Random mating and a lack of epistasis are
  necessary to obtain a good relationship between
  actual and predicted values
• Formula suggest that Syn or F2 performance can
  be improved by
• increasing the combining ability of the parents
• increasing the number of parents
• increasing the performance of the parents
• However, as n increases, MP and MF1 tends to
  decrease

22
Example of expected (predicted) and actual yields
using the F2 or synthetic-2 (Syn2) prediction
formula F2 MF1 (MF1 MP) / n
For single crosses F2 MF1 (MF1 MP) / n
Expected F2 62.8 (62.8 23.7)/2 62.8
19.55 43.3 For 3-way crosses Expected F2
64.2 (64.2 23.8)/3 64.2 13.5 50.7
23
Example of expected (predicted) and actual yields
using the F2 or syn2 prediction formula F2 MF1
(MF1 MP) / n
For single crosses F2 MF1 (MF1 MP) / n
Expected F2 62.8 (62.8 23.7)/2 62.8
19.55 43.3 For 3-way crosses Expected F2
64.2 (64.2 23.8)/3 64.2 13.5
50.7 HOWEVER in predicting the performance of
the Syn2, n would be the number of clones or
lines in the intercross block and NOT 2 which
would be the maximum number of parents in any
particular Syn-1 hybrid, i.e. you can only have
single crosses among the clonal parents to
produce the Syn-1. Thus formula will under
estimate SYNETHIC-2 performance if n2 is used as
in the single cross above, OR PROBABLY over
estimate as n increases and the absolute value of
n is used.
24

• Breeding Methods in Cross-Pollinated Crops
• Synthetic cultivars (additional comments)
• Performance of Synthetic cultivars (contid)
• The number of Synthetic Cultivars increases with
  the number of potential parents since a Syn can
  be composed from 2 to many lines/clones
• Parents possible synthetics
• 4 11
• 8 57
• 12 4,083
• n 2n n 1

25

• Breeding Methods in Cross-Pollinated Crops
• Synthetic cultivars (additional comments)
• Performance of Synthetic cultivars (contid)
• The number of Synthetic Cultivars increases with
  the number of potential parents since a Syn can
  be composed from 2 to many lines/clones
• Parents possible synthetics
• 4 11
• 8 57
• 12 4,083
• n 2n n 1

with parents 1, 2, 3, and 4 1234 12 13 123 14
124 23 134 24 234 34
26

• Breeding Methods in Cross-Pollinated Crops
• Synthetic cultivars (additional comments)
• Factors to consider in developing a polycross
  nursery
• clones must flower synchronously
• adequate isolation
• replication is essential to random pollination
  (consider that adjacent clones are more likely to
  intermate that more distant clones
• most common designs are RCB and Latin Square
• harvest seed from each clone within each rep
  separately and bulk a similar quantity from each
  to help insure random mating
• Similar to a blend but a blend or multi-line but
  these have to be reconstituted each year

27
Breeding Methods in Cross-Pollinated
Crops Synthetic cultivars (final thought) If
Hardy Weinberg is accurate then why is an
advanced synthetic any different than a first
generation synthetic? Consider the development of
a Synthetic of 2 clones, BB and bb, and consider
that B has survival fitness but not economic
fitness Initial intercross block BB and
bb Harvest seed and sell as Synthetic-1 and it
has a genetic makeup of 0.25BB 0.50 Bb 0.25bb
OR 50 of the plants are F1 hybrids Harvest
seed of Synthetic-1 to produce Syn-2 and you are
increasing the frequency of B which is
economically detrimental. etc. So Synthetics
are based on an idealized HWE but with the
understanding of possible realities. (already
noted epistatic problems)