Agriculture Reference
In-Depth Information
the case of
Fusarium
on cereal seeds. For some seedborne diseases additional postharvest, non-
chemical treatments are needed, such as hot water or hot air treatments (Forsberg
et al
. 2000).
However, more research is needed to optimise such methods to reduce the risk of damaging
the seed (Jahn
et al
. 2004). Next to these physical treatments, disinfecting coatings with natural
compounds are being developed, such as organic acids (mustard powder) or essential oils
(thyme oil) (Groot
et al
. 2004). In seed potato there are positive results with treatments against
Rhizoctonia solani
with the antagonist
Verticillium biguttatum
(Hospers 1996).
For some crops there is no problem in meeting the quality standards as required for con-
ventional seeds, but in some cases the thresholds for seedborne diseases are adjusted (Nielsen
2003; Lammerts van Bueren
et al
. 2003a; Girsch and Weinhappel 2004). In some countries the
recommended tolerances or thresholds for some diseases are lowered. In Austria, for instance,
the threshold for
Fusarium nivale
has been adjusted from 20% in conventional agriculture to
10% for the organic sector. In the Netherlands, the level of permitted contamination in organic
seed potato has been lowered from 25% (conventional) to 10%. A lower threshold is also set in
other diseases, for example, in Austria, 10% is permitted for
Septoria nodorum
in cereals,
compared with 20% previously.
Plant breeding
Genetic diersity
Modern varieties have been developed with the aim of combining high productivity and
uniform product quality under high input conditions. The situation concerning the G × E × M
interaction is different for organic farming systems and thus, the goal for breeding programs.
First, under low-input conditions farmers have to cope with more biotic and abiotic stresses
and larger environmental variation within and between farms, so the E is high. Second, an
organic farmer has fewer means to overrule that variation, so the M is low. This has conse-
quences for the genetic input (G) and the demands on varieties are therefore higher (see
Yield
stability and plant health)
. Organic farmers search for new varieties that possess a combination
of required characteristics to increase yield stability under low-input, organic conditions. The
question is how breeding can contribute to adapting crops and varieties to the organic, lower-
input environment by improving the inherent buffering capacity of the farm system, and
thereby, yield stability.
Modern varieties, such as those available for wheat, commonly lack the ability to adapt to
different and changing environments, including drier regions with less fertile soils such as
southern Australia (Kitchen
et al
. 2003). The tendency in conventional breeding is to select for
single genotypes that have general adaptation to a large area where the variation in environ-
ments largely can be overruled by high inputs. Such varieties are 'generalists' and are not nec-
essarily superior for nor adapted to a specific environment. As organic farming systems have
fewer means to overrule agrodiversity, the variation in environmental conditions is larger, and
therefore the need for a larger variation of so-called specialist varieties exists. But developing
specialist varieties is difficult to achieve economically. Second, organic varieties need a certain
degree of buffering capacity, which means that the conventional pedigree line breeding may
have its limits on the performance of crops, such as wheat, in organic agriculture. Next to that
problem, the current new varieties are mostly derived from a limited number of parental lines
and are thus genetically closely related to each other.
The genetic base for an organic breeding program should be broadened and newly estab-
lished. This aspect of broadening the base is even more important when searching for adapta-
tion to organic farming. A broader genetic base can be achieved by creating composite cross
populations followed by selection under organic farming conditions. In composite crosses
