In Vitro Screening

"The right to search for truth implies also a duty; one must

notconceal any part of what one has recognized to be true."        Albert Einstein, 1879-

1955

"The right to search for truth implies also a duty; one must

notconceal any part of what one has recognized to be true."        Albert Einstein, 1879-

1955

Definition: Selection vs Screening

Selection:1.The process by which some individuals come to contribute more offspring than others to form the next generation through intrinsic difference in survival and fertility or the choice of parent by the breeder2.The process determining the relative share allotted individuals of different genotype in the propagation of a population3.The process by which certain organisms multiply while other are less suited surrounding and die out

Definition: Selection vs Screening

Screening:1.An investigation of a large number of organisms for the presence of a particular property2.Use of a screen3.Examining the properties, performance response of individuals, lines, genotypes or other taxa under an assortment of condition in order to evaluate the individuals or groups

Selection1. The central step of the breeding

process2. The success depends on the ease and

speed with which the superior plant within a segregating population can

be identified3. In classical breeding, selection is

carried out on huge populations normally in the fields

4. Field selections are strongly influenced by environmental

condition5. There are uncertain and lengthy, especially in the case of breeding for

quantitative characteristics with a polygenic background

Selection methods

The most common breeding procedure was mass-The most common breeding procedure was mass-selection which in turn was subdivided into negative selection which in turn was subdivided into negative and positiveand positive

Negative selectionNegative selectionThe most primitive and least widely used method The most primitive and least widely used method which can lead to improvement only in exceptional which can lead to improvement only in exceptional cases cases implies culling out of all poorly developed and less implies culling out of all poorly developed and less productive individuals in a population whose productive individuals in a population whose productivity is to be genetically improvedproductivity is to be genetically improvedThe remaining best individuals are propagated as The remaining best individuals are propagated as much as necessarymuch as necessary

Positive selectionPositive selectionOnly individuals with characters satisfying the Only individuals with characters satisfying the breeders are selected from population to be used as breeders are selected from population to be used as parents of the next generationparents of the next generationseed from selected individuals are mixed, then seed from selected individuals are mixed, then progenies are grown together progenies are grown together

Production and Use of Variability

1.Conventional breeding

Combination Breeding (Cross Breeding) Mutation Breeding Chromosome transfer (wide hybridization)

2. Modern breeding

Cell fusion Soma-clonal Variation Gene transfer

Selection

1. On the whole plant

Field trials Green-house trials Laboratory trials (in vitro selection)

2. On the simple genome (in vitro selection)

Haploid selection Single cell selection DNA probes

The Advantage of In-vitro Selection

1. Freedom from the effect of climate and natural environment, which make it easier to measure slight difference in polygenic inherited traits horizontal or general disease resistance

2.The ability to handle large numbers of individuals in a very small space

3.The ability to work with the simpler genome of which allows the uncovering of recessive traits and additive characters within a relatively small population

Target of Invitro SelectionWhole plant (Seed/embr

yo)

Organ

Tissue

Single Cells

DNA

1. Seedlings of a culture filtrate from Leptosphaeria masculans (disease resistance)

2. Rice seedlings of salt enrichment media (Mineral tolerance)

1. Leaf segment of young barley with standardized spore of powdery mildew (disease resiantance)

2. Petiole culture of sugarbeet on salt enrichment media (mineral tolerance)

1. Selection of somaclonal variation (disease resistance, environmental tolerance)

2. Selection using a selective agent (disease resistance, salt tolerance, metals tolerance, temperature stress tolarence, herbicide tolerance)

1. Selection for biotic stress resistance2. Selection for a-biotic stress tolerance (cold, heavy metals, herbicide)

1. Quantitative trait loci2. Marker assisted Selection3. Marker assisted backcrossing

It would emphasize here the necessity of growing all in vitro selected plants in

the fieldVery often a powerful in vitro tolerance

does not show up at the whole plant level under field condition