Agriculture Reference
In-Depth Information
Table 5.2
Variety characteristics supporting plant health in organic crop production
Mechanism
Variety characteristics
Escape
Shorter crop growth period and/or early ripening to be able to avoid the
critical infestation period, or to have enough yield before the infestation
becomes too severe (potato/late blight; onion/downy mildew; carrot/carrot
fly)
Resistance
One or more monofactorial and multifactorial, durable resistance traits
against pest and disease affecting yield and/or quality (scab/apple, late
blight/potato, lettuce/downy mildew, yellow and brown leaf rust/wheat);
weed competition by an allelochemical ability
Tolerance
Morphological or physiological traits to support reducing the risk of a rapid
expansion of the infestation, such as for cereals: long stem, ear high above
flag leaf, ear not too compact; leaf erectness/onion; hairy and tougher
leaves against aphids/potato; wax layer on leaves against fungi/onion/
cabbage.
Stress tolerance in general by good adaptation to low(er)-input and organic
inputs, ability to cope with fluctuating N-dynamics, efficient capturing of
water and nutrients, deep and intensive root architecture; ability to interact
with beneficial soil microorganisms, like mycorrhizae and atmospheric N-
fixing bacteria; efficient nutrient uptake and high nutrient use efficiency.
Plant architecture for early soil cover and more light-competition.
Good combining ability in variety and species mixtures
Recovering ability
Good ability to recover from mechanical harrowing/cereals; high seedling
vigour, fast and high germination percentage; deep and intensive root
architecture
(Lammerts van Bueren
et al
. 2004b) and potato. In the case of fruit, a skin with a sufficiently
thick natural wax layer, instead of a skin coated with synthetics, can positively inf luence longer
storability. Organic bakeries try to avoid synthetic additives in the bread-baking process, but
then require varieties with high baking quality and still sufficient yield under lower input con-
ditions (Kunz
et al
. 1995; Kunz 2000; ITAB 2001; Welsh
et al
. 2001). Another aspect of quality
is taste. Sensory qualities, such as taste, are not only a result of environmental and manage-
ment factors but also of genetic inf luences. Although sensory quality has been added to organic
breeding programs of carrot (Hagel
et al
. 2000), genetic variation for quality traits has not yet
been fully explored.
Crop ideotypes
Priorities for required traits differ for each crop and market sector. To improve the communi-
cation between farmers, traders and breeders, crop ideotypes should be elaborated and
designed for each crop. In the short run such crop ideotypes can contribute to a more adequate
selection of appropriate varieties among the existing assortment of conventional varieties. But
they are also necessary to achieve selection criteria for new varieties from breeding programs
specifically focused on low-input and organic agriculture (Osman and Lammerts van Bueren
2002). Organic crop ideotypes have many selection criteria in common with conventional
required traits, such as disease resistance and high yielding ability. The difference is that varie-
ties for organic farming have to be able to perform well under low-input conditions. Another
difference is additional supporting characteristics for plant health and yield potential, such as
long stems, the ears being high above the f flag leaf, and the ears not too compact. But also a
characteristic such as a long stay green index for the top leaves in wheat is very important to
enhance photosynthesis during the final phase of grain filling (Lammerts van Bueren
et al
.
2002).
