Plant Breeding - Guido Flashcards
What are the three phases of crossing genotypes to produce a progeny
- Identify populations / collections of germplasm characterized by genetic variability
- Select individuals with superior phenotypic characteristics
- Develop improved varieties from these individuals
What is a quantitative character
a measurable character, with a continuous distribution of phenotypes (polygenic, multifactorial or complex
characters)
Phenotypes are produced by
the action of many genes and their interaction with the environment
What is QTL - Quantitative Trait Loci
Genomic regions containing genes associated with a quantitative character are known
Can different genotypes have the same phenotype
Yes, Many different genotypes can have the same phenotype
The greater the number of loci involved in
determining a character, the________the
number of possible genotypes
greater
Inheritability is defined as the relationship between
phenotypic variation, due to environmental and genetic causes
Inheritance refers to the process by which genetic information is passed from parents to their offspring
heritability refers to the proportion of the variation in a particular trait within a population that can be attributed to genetic factors. It is a statistical measure that estimates the extent to which differences in a trait among individuals can be attributed to genetic variation
Why cant the influences on the phenotype be broken down into genetic
and environmental components
because the expression of the genotype depends on the environment in which the plant grows
total phenotypic variance equation
VP = VG + VE + VGxE
VP: variance in phenotype
VG: genetic variance
VE: environmental variance
VGxE: genetic variance x environ. variance
phenotype
plant traits, everything you can see, until you can prove it is genetics inherited
another word for genotype propagation
cloning
additive genetic variances (VA)
additive effects that can be added to determine the overall effect on
the phenotype
Genetic variance due to dominance (VD)
genes with a dominant component - the effect of an allele depends on the identity of the other allele for the same locus
Genetic variance due to interaction (VI)
genes that interact with each other having epistatic (completely new) effects - which is not present when the action is limited to single genes
genetic variance equation
VG = VA + VD + VI
VG: variance in genetics
VA: additive genetic variances
VD: genetic variance due to dominance
VI: genetic variance due to interaction
phenotypic variance (VP)
attributed to differences between the population genotypes
environmental variance (VE)
due to non-genetic factors, such as different amounts
of light
The variance due to the genotype - environment interaction (VGE)
occurs when the effect of a gene depends on the specific environment in which it is found
The total phenotypic variance equation
answer: VP = (VA + VD + VI) + VE + VGxE
because:
VP = VG + VE + VGxE
VG = VA + VD + VI
VP: variance in phenotype
VG: genetic variance
VE: environmental variance
VA: additive genetic variances
VD: genetic variance due to dominance
VI: genetic variance due to interaction
Broad sense inheritability (H2 or hb2)
-equation
-definition
-ranges
H2 = VG / VP
-the portion of phenotypic variance determined by total genetic variance
-H2 ranges from 0 to 1
VG: genetic variance
VP: variance in phenotype
Explain the range for broad AND narrow sense inheritability and what it means
0 = differences due solely to environment
1 = differences due solely to genetics
closer to 1 the greater the genetic component
narrow sense heritability (hn2)
-equation
-definition
-ranges
hn2 = VA / VP
-phenotypic variance directly transmitted from parents to offspring
-always less than or equal to broad-sense heritability.
Broad-sense heritability accounts for total genetic variance (additive, dominant/recessive, and interactive), while narrow-sense heritability only accounts for additive genetic variance.
-ranges 0-1 (The closer to 1, the greater the Additive genetic component)
How can you estimate inheritability in a broad sense - through variance decomposition
by eliminating one of the components of the
variance; make VG or VE 0
VG = 0 by cultivating genetically identical individuals (preferred)
VE = 0 by all individuals cultivated in the same environmental
conditions (NOT possible)
Estimation of heritability through parent-offspring regression
-Parental phenotypes are compared with those of progeny individuals
-if the genetic differences are the most responsible for the phenotypic variation, a progeny should look a lot more like the parental compared to unrelated individuals
r2
regression coefficient
-provides an estimate of inheritability in the strict sense
species resistant to iron chlorosis, and how
V. vinifera and V. berlandieri (the best)
There are genotypes of grapevines able to reduce iron in the soil by acidification of the environment with a proton release (not sure if these two species do this)
How can you measure a vines resistance to chlorosis
The concentration of chlorophyll in the leaf of
plants grown on calcareous soils is a measure of resistance to chlorosis
The quantitative components of production (vigor, production per plant, weight of clusters, length of clusters) have a ______ heritability
The qualitative characteristics of the production
appear to be under ________ genetic control
-low
-strong
The number of clusters per plant is determined largely
by genetic causes
The vigor is __________ correlated with acidity and _______________ correlated with the sugar / acid content ratio
positively
negatively
The number of clusters is ___________correlated with the size and weight of the berries and acidity
negatively
The length of the bunches is ___________ correlated with the sugar content and acidity
positively
What is the most planted grape in the world
Kyoho (and then Cab sauv)
Rpv1 and Run1
Downy mildew (Plasmopara viticola)
Powdery mildew (Uncinula necator f.c. Oidium tuckerii)
Plant disease resistance protects plants
from pathogens how
two ways:
1. preformed structures and chemicals
2. infection-induced responses of the
immune system
Host Plant Resistance (HPR)
Those characters that enable a plant to avoid, tolerate or recover from attacks of a pathogen under conditions that would cause greater injury to other plants of the same species
what % of seeds are germinated during regular pollination versus human aided pollination
50% normal germination
10% human aided
Non-host resistance or basic incompatibility
-Plants repel the attack of pathogenic fungi - passive or active
-plant defense barriers (thick cuticle, synthesis of toxic substances) and / or inducible defense mechanisms
-The pathogen may not possess the means to overcome these chemical / physical barriers that
prevent its colonization of the plant tissues
basic passive resistance is based on
the constitutive expression of physical or chemical
barriers, the defense mechanism is always present and operative
active basic resistance is activated following - compatible or not?
an attack,
-is triggered in a non-specific way by
generic substances detecting the presence of microorganisms
-basic incompatibility
Host-plant resistance or basic compatibility
-The plant becomes a host plant for that pathogen
-The attack on a plant by a pathogen is a rare exception and is made possible by the pathogen’s
production of pathogenic factors acquired during the evolution
Basic compatibility or incompatibility?
1. Host-plant resistance
2. Non-host resistance
- Host-plant resistance = basic compatibility
- Non-host resistance = basic incompatibility
What is vertical resistance in plants?
A plant variety that exhibits a high degree
of resistance to a single race, or strain,
of a pathogen; this ability usually is controlled
by one or a few plant genes
What are disease resistance genes? (R-Genes)
genes in plant genomes that convey plant
disease resistance against pathogens by
producing R proteins.
main class of R-genes consist of a nucleotide binding
domain (NB) and a leucine rich repeat (LRR) domain(s) and are often referred to as (NB-LRR) R-genes or NLRs
Vertical versus horizontal resistance to plant disease; specific or nonspecific
vertical = specific - resist only some races
-can be bypassed by a single mutation in pathogen
horizontal = nonspecific - resist all known races
-more stable over time, though not as efficient as vertical resistance
What is gene-for-gene resistance in
plants?
the elicitors are coded by the avirulence genes (avr) of the pathogen while the receptors are encoded by the genes for the resistance of the host plant (r)
Active plant defense triggered when a plant resistance (R) gene recognizes the intrusion of a specific
insect pest or pathogen.
hypersensitive response
it occurs very rapidly at the site of infection
Systemic Acquired Resistance (SAR)
-for SAR to occur the first infection causes a ‘hypersensitive reaction’ response
-The molecular signal that is translocated in the plant and which stimulates the SAR trigger in a systemic way is salicylic acid
Is plant disease resistance genetic?
Yes, but disease resistance genes in plant cultivars can break down in the field due to the evolution of pathogens under high selection pressure.
_______________ is based on single genes whereas
_______________ depends on two or more genes
monogenic resistance
quantitative resistance
What is quantitative resistance?
-incomplete or partial level of resistance phenotype
-continuous distribution between resistant and susceptible phenotypes in a progeny, most often resulting from the segregation of alleles with variable
effects at several loci
How many disease resistant (fungi, bacteria, virus) genes are currently known, how is their reactions similar
-About 30 genes of resistance to different diseases are known in different plant species
-All of them trigger the hypersensitivity reaction
-Grapevine has about 500 resistance genes, but it is not resistant to pathogens imported from the New World
Why are some plants resistant to some pathogens
-It is widely believed that plant species have evolved in their centers of origin along with their own pathogens
Resistance to downy mildew (Plasmopara viticola)
-The disease is caused by an oomycete,
-Plasmopara is an absolute and obligatory pathogen.
-It completes its life cycle only on green vine
tissues
-can not be grown in vitro
-Almost all species of American species and many Asian species have genes of resistance (including V. Amurensis)
-V. vinifera completely susceptible
-Muscadinia rotundifolia completely resistant
main chromosome(s) that determines the downy mildew resistance
-chromosome number 18 of the genome of the American vitis vines (18 controls the appearance of the hypersensitivity reaction)
-in Muscadinia there is an additional gene placed on chromosome number 12 (they have both)
Why can’t V. vinifera create a hypersensitivity reaction to downy mildew, and why can American Vitis?
V. vinifera is homozygous recessive and the resistant species are homozygous dominant
Resistance to downy mildew (Plasmopara viticola) is due to these two major genetic systems
- the hypersensitivity reaction, activated by a single gene
- the polygenic system, which determines the inhibition of mycelium growth in the host due to the synthesis of phytoalexins, stilbenes, reactive oxygen species and defense proteins
Resistance to powdery mildew (Uncinula necator, conidic form Oidium tuckerii)
-an ascomycete
-obligate parasite
-can not be grown up ‘in vitro‘
-main sources of resistance are among Vitis cinerea, V. rupestris, V. labrusca, V.riparia, V.aestivalis
-Vitis with 38 chromosomes - polygenic and resistance from chromosome 15
-for Muscadinia rotundifolia (chrom 40) - monogenic and resistance on chromosome 12
-V. vinifera from Uzbekistan has resistant gene located on chromosome 13 (first case of a fungus resistance gene, evolved in a Vitis vinifera!)
-Ren12 was recently found in V. amurensis BUT for the test question, V. amurensis is NOT resistant to PM
Resistance to Botrytis (Botryotinia fuckeliana, conidic form Botrytis cinerea)
-a necrotrophic fungus, produces cell wall degradation enzymes, toxic levels of reactive oxygen species (ROS) and generic toxins resulting in the maceration of plant tissues
-resistance is never due to a single gene
- Phytoalexins of the stilbenes (resveratrol, viniferins, synthesized by some ‘tolerant’ genotypes) class have a toxic effect on the growth of the fungus
- tolerant plants have expression of proteins linked to pathogenesis inhibitors (glucanases, chitinases and polygalacturonidase)
-It is not a total resistance
-slow reaction 6-24h activation, enzymes present for 3-7 days
