Transcript Breeding for Resistance

Breeding for Resistance
Control important crop diseases and pests
Must have genetic variability
Consider both genetic variability in the plant
and in the pest
Sources:
Fehr, ch. 21
Slusarenko, Fraser, and van Loon, 2000
Types of Genetic Resistance
•
Qualitative Resistance
• Distinct classes of resistance and susceptible plants
• Controlled by one or a few genes
• Also called “Vertical” resistance
•
Quantitative Resistance
• Continuous variation among genotypes
• Many loci
• Also called “Horizontal” resistance
Qualitative Resistance
 Controlled by major genes (one or two)
 Genes are readily transferred from one
genotype to another
 Presence of genes can be determined
by exposing plants to particular races
Qualitative Resistance
Advantages
Easier screenings
Easier transfer of genes “all or nothing”
Disadvantages
Vulnerability to new races
Continuous use of particular cultivar may
lead to development of new race or shift in
pest population (shift from race 1 to race 2)
Qualitative Resistance
Examples:
Leaf Rust Resistance in Wheat
Quantitative Resistance
Controlled by many genes each with minor
effects
Advantages
 Can control a broad range of races due to the
fact that many loci are involved
Disadvantages
 Difficult to transfer resistance from one genotype to
another
 Individual genes harder to identify
Quantitative Resistance
Examples:
Fusarium Head Blight in Wheat
Sources of Resistance
Primary Gene Pool
Other breeding programs
Landraces
Germplasm collections (GRIN)
Wild Relatives
Tomato: Lycopersicon genus
Wheat: Agropyron genus
Aegilops tauschii, Triticum monococum
Mutant Transformations: powdery mildew in Barley
Vertical vs Horizontal Resistance
Resistance
Susceptibility
1
2
3
4
5
6
Races
Vertical Resistance to Races 2, 5, and 6
Vertical vs Horizontal Resistance
Resistance
Susceptibility
1
2
3
4
5
6
Races
Horizontal Resistance to all Races
Hypersensitive Response
Stem Rust of Wheat
Programmed cell death
A lot of black boxes
Pathogen recognition,
signaling proteins,
transcription factors,
Gene-for-Gene Hypothesis
Proposed by Flor (1956)-study on flax rust
“For each resistance gene in the plant
there is a gene in the pathogen that
determines if the pathogen will be able to
injure the plant.”
Gene combinations and Disease Reaction
Types in the Gene for Gene concept
Virulence or
avirulence
genes in
pathogen
R (resistant,
dominant)
R
(susceptible,
recessive)
A dominant
AR (-)
Ar (+)
a recessive
aR (+)
Ar (+)
Complementary Interaction of Two Host Genes
For Resistance and the Corresponding Two
Pathogen Genes for Virulence
Resistance R or susceptibility r
genes in the plant
R1R2
R1r2
r1R2
r1r2
Virulence
a or
Avirulence
A genes
In the
pathogen
A1A2
-
-
-
+
A1a2
-
-
+
+
a1A2
-
+
-
+
a1a2
+
+
+
+
Races of Pests
 Genetic variability within the pathogen
population
 Different isolates cause different responses
among host genotypes
 Example: Soybean Cyst Nematode Races
Minimizing Changes in Races
 Alternation of Resistant and Susceptible
Cultivars (soybean cyst nematode)
 Mixtures of Resistant and Susceptible
Genotypes
 Prevention of New Races
Resistance vs Tolerance
Resistance: no establishment of the
pathogen in/on the host, or a limited
establishment
Tolerance: the host develops,
continues to grow, and produces well
despite the pathogen’s presence
Breeding for Specific Resistance
 Individual Major Genes
 Multilines
 Pyramiding
Breeding for Specific Resistance
Individual Major Genes
 Breed cultivars with major genes that
control the prevalent pest races
 Select progeny from a segregating
population or …
 Transfer major genes from other sources
 Example: Black Shank Tobacco Varieties
 Advantages and Disadvantages
Breeding for Specific Resistance
Multilines
 Develop many individual lines each with
individual major resistance genes and then …
 Mix the seed of these lines together to get …
 Protection against a broad spectrum of races
 Example: wheat cultivar Miramer 63
 Advantages and Disadvantages
Breeding for Specific Resistance
Pyramiding
 Put all known major genes into one line
 Advantages and Disadvantages
 Example: Leaf Rust in Wheat
Comparative structural analysis of the Lr10 homologous regions from
diploid wheat, rice 5 (japonica), indica rice and rice 1 (japonica).
Lr10
QTL and Resistance
 Quantitative Trait Loci
 Identify QTL that control variation in
resistance observed in genotypes
 Use markers to screen genotypes (throw out
the susceptibles)
 Applications in Marker Assisted Selection
(MAS)
QTL and Resistance
Wheat
chromosome 1A
Source:
J.C. Nelson et al.
1997 Crop
Science 37:19281935
Leaf rust gene
‘Lr10’
QTL for Fusarium Head Blight Resistance in
Wheat
Ning 7840/Clark population
11 AFLP markers associated with resistance
1 marker explained 53% of the variation
Bai, Kolb, Shaner, and Domier. Phytopathology 89:343-348.
Sumai 3/Stoa population -- used RFLP markers
5 genomic regions were associated with
resistance (3 from Sumai 3, 2 from Stoa)
Waldron, Moreno-Sevilla, Anderson, Stack, Frohberg. Crop Sci 39:805-811.
Example of Quantitative Genetics
 3 F2:3 populations, 40 families, 3 reps,
13 individual observations per rep
 Separated variance into two parts
Among families

Within families
 W   WG  
2
G
2
2
2
 Narrow sense heritabilities were
estimated
WE
ANOVA
Source
Among Families
Within Families
df
39
1496
MS
EMS
5393.49
W  39G
965.72

2
2
W
2
Example from Population 2
 113.53
2
  965.72
2
  835.70
2
G
   
2
2
G
A
1
4
2
D
W
WE

2
WG
130.02
Estimate from 2555

2
W G
 A  D
1
2
2
  64.69
2
A
 195.35
2
D
1
2
2
Genetic Parameters and h2 of FHB Severity
Pop 1
Pop 2
Pop 3
73.77
64.69
118.17
89.43
195.35
0.00
0.12
0.06
0.12
h 2(NS) F 3 x
0.64
0.39
0.69
G
12.14
8.88
15.89


2
A
2
D
h ind
2