Plant breeding for organic and sustainable, low-input agriculture

Quantitative-genetic basis of breeding maize
for adaptation to organic and low-input farming
Hartwig H. Geiger 1 , Walter Schmidt 2 , Henriette Burger 1
1 University of Hohenheim, Stuttgart, Germany
2 KWS SAAT AG, Einbeck, Germany
Ecologically sustainable production of healthy food has become a major goal in present-day
farming. Nutrient-efficient crop varieties with specific adaptation to organic farming may
significantly contribute to achieve this goal. This paper presents quantitative-genetic data on the
perspectives of breeding such varieties in maize.
Large representative samples of testcrosses from the current KWS breeding program were
evaluated under N-deficiency (LN = low N) and conventional (HN = high N) conditions in
multi-environment field trials. In subsequent experiments additional testcross series, synthetic
populations, and landrace-derived haploid (DH) lines were compared under organic (OF) and
conventional (CF) farming conditions.
Soil nitrogen deficiency caused an average grain yield reduction of about 35-50 %. Phenotypic
correlations between LN and HN were moderate to high for random samples of test-cross
materials and low to moderate for single crosses selected for specific adaptation to LN or HN
conditions. Significant genetic variation existed for the reaction to N-deficiency stress.
Heritability coefficients were similar under LN and HN. Molecular marker studies revealed eight
quantitative trait loci (QTL) for yield under LN jointly explaining 70 % of the genotypic
variance. Growth chamber studies indicated that lateral root development of seedlings correlates
with tolerance to N-deficiency.
Grain yields under OF compared to CF were reduced by 5 - 25 % depending on the test
environments and, to a lesser extent, the genetic material. Only small to moderate phenotypic
correlations existed between OF and CF for grain yield but strong ones for plant height and dry
matter content. Re-evaluation of the top genotypes confirmed their specific adaptedness to OF or
CF or both. Testcrosses of landrace-derived DH-lines were about 20-25 % lower performing
that those of modern inbred lines, but the difference was smaller under OF than under CF. Open
pollinated populations synthesized from superior inbred lines performed much lower (20 - 30 %)
than predicted by quantitative genetic theory. Again, the difference was smaller under OF.
Data demonstrate that significant genetic variation exists in modern Central European maize
germplasm for tolerance to N-deficiency and adaptedness to organic farming. Extending the
scope of hybrid maize breeding to these attributes should soon furnish varieties satisfying the
needs of low-input and organic farming.
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