Plant breeding for organic and sustainable, low-input agriculture

Quantifying genotype and environment interactions to benefit selection and evaluation of
cereals for competitiveness against weeds
S.P. Hoad and C.F.E Topp
Scottish Agricultural College, Edinburgh, Scotland, UK.
Traits for weed suppression are important in the selection of cereals for organic farming and
sustainable low-input agriculture. The environment, including both seasonal and management
factors, has a significant impact on the ability of a genotype to suppress weeds.
Selection and evaluation of new genotypes would benefit from a better understanding of the
relative contributions of genetic variation and genotype x environment interactions on key plant
traits and crop characteristics for weed suppression.
This includes important measures such as: (1) an early prostrate habit at the start of tillering
combined with a high leaf area index; (2) high shoot population density that is a function of plant
number and the ability of a plant to produce and maintain tillers; (3) rapid early growth allowing
the crop to maintain a light interception lead over the rapidly growing weeds, and with an
appropriate growth habit, shade newly emerging weeds and (4) increased plant height that adds
to competitiveness at moderate to high plant population densities, as well as increasing tolerance
to weeds.
Generally, a high season-long crop ground cover is important. Crop ground cover integrates
several plant and crop characteristics. In fact, ground cover is strongly influenced by genotype x
environment x crop management interactions. High ground cover by the crop at the end of
tillering is strongly correlated with weed suppression up to full canopy cover and even to harvest.
The balance between different characteristics for weed suppression will determine the value of a
genotype, for early, late and season-long weed control. It is clear that selection for genotypes
should be considered in relation to climatic factors that affect both crop and weed growth.
For plant breeders, selection and evaluation of genotypes should be based on an understanding
the role of different characteristics in weed competition under organic farming or low-input
conditions.
Genotypes for organic agriculture need to be more robust in both their percentage establishment,
under contrasting conditions, and in their ability shade weeds, through increased ground cover,
that is complemented by beneficial effects of increasing tiller production and plant height.
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