2012 CIOPORA Chronicle

RFLP
The introduction of RFLP gave
again a boost to the idea of what
we now call “molecular breeding.”
(Tanksley et al. 1989).
“Now restriction fragment length
polymorphism (RFLP) linkage maps
are being constructed for most major
crop plants and these maps provide
a more direct method for selecting
desirable genes via their linkage to
easily detectable RFLP markers.
The integration of RFLP techniques
into plant breeding promises to: (1)
Expedite the movement of desirable
genes among varieties, (2) Allow the
transfer of novel genes from related
wild species, (3) Make possible the
analysis of complex polygenic characters
as ensembles of single Mendelian
factors, and (4) Establish genetic relationships
between sexually incompatible
crop plants. In the future, high
density RFLP maps may also make it
possible to clone genes whose products
are unknown, such as genes for disease
resistance or stress tolerance.”
Despite the enthusiasm, does this
mean that at this moment, there
still is a lack of technological resources
to meet the demands from
the breeding industry? Research
during the last decades has added
fundamental knowledge from both
model species and crops. This has
revealed the mechanisms behind
many important features e.g. the
understanding of disease resistance.
But quite often, extra knowledge
also demonstrated the complexity
behind, tempering the initial
expectations. When considering
available marker technologies, one
moved from anonymous markers
to candidate genes, from 5
markers per chromosome to an
average of 1 SNP marker per 1000
bp and a whole scala of candidate
genes. Throughput tremendously
increased by more data points per
run every year or new technology
platform introduced. Especially,
current automated fingerprinting
systems result in an enormous
labour reduction. And finally, new
statistical techniques and appropriate
software tools fit the need for a
more sophisticated data analysis.
>>>
The costs of implementing molecular breeding can be controlled by doing the simple things in house and outsourcing
the advanced technology.
Some rules of thumb
Some rules of thumb for application of markers versus phenotypic selection
in breeding for ornamentals and fruits
New combinations using “exotic” germplasm
– Aiming for “lucky shots” Phenotype
– Interspecific hybrids, “far”... Markers will NOT help you
– Introgression, against background Markers supported by phenotype
Disease resistance (and other “simple” traits)
– Reliable screening test Phenotype
– Few genes, difficult screening Markers
– Many genes, difficult screening Phenotype supported by markers
Plant quality, traits related to culture conditions
– Easy screening Phenotype
– Difficult screening, clear genetics Markers
– Time consuming, progeny testing Phenotype but invest in markers
– Screening and genetics difficult Important traits only: QTL mapping
CIOPORA Chronicle April 2012 | www.CIOPORA.org 41