Plant breeding for organic and sustainable, low-input agriculture

Potentials of molecular markers to exploit G x E interactions for organic farming
Gunter Backes 1 , Hanne Østergård 2
1 University of Copenhagen, Faculty of Life Sciences, Frederiksberg, Denmark;
2 Risø National Laboratory, Technical University of Denmark-DTU, Denmark
One of the substantial differences between conventional and organic farming is the degree to
which the farmer has the possibility to implement short-term changes of environmental factors.
This implies that organic farming carries along a higher environmental dependency and thereby a
much greater focus on genotype × environment interactions (GEI). GEI is often neglected in
practical breeding and breeding research due to 1) high complexity, 2) lack of procedures in a
breeding pipeline, and 3) variety approval system building mainly on traits per se, not on GEI.
While the latter is based on political decisions, there is help ahead for the first two issues using
molecular markers and marker-assisted selected (MAS). However, within the organic sector
there is much debate about the application of molecular markers with respect to the methods
used in marker establishments as well as the integrity of plants (Lammerts van Bueren et al.,
2005)
Recent developments of knowledge on genetic networks and physiological systems, together
with new approaches for the analysis of the relation of genetic marker data with phenotypic
traits, make it possible to analyze not only the effect of a gene on a trait (the phenotype), but the
effect of a system of genes as a response to environmental influences (van Eeuwijk et al., 2005).
Encouraging results from this approach have been obtained in pilot studies, especially in cases
where GEI is important, e.g., yield under stressed conditions (Vargas et al., 2006). In relation to
breeding for organic farming, this approach and MAS could gain importance on several levels:
(a) the way breeders deal with the traits and their environmental influence; (b) the identification
of conventional bred varieties with desirable GEI reaction pattern; (c) direct application of MAS
for GEI reaction patterns in breeding for organics. The latter depends on costs of molecular
analyses and the market potential of varieties for organic farming as well as on ethical considerations
within the organic sector. Still, future experience has to show if this application of markers
is superior to a traditional selection that directly selects on the trait and indirectly on the gene.
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