3233: Thresholds for Net Blotch Infestation in Organic Barley Seed Production

Pinnschmidt, Hans O.; Nielsen, Bent J. and Hansen, Henrik J. (2004) Thresholds for Net Blotch Infestation in Organic Barley Seed Production. Poster presented at The First World Conference on Organic Seed: Challenges and Opportunities for Organic Agriculture and the Seed Industry, Rome, 5-7 July 2004; Published in Lammerts van Bueren, E.; Ranganathan, R. and Sorensen, N., Eds. Proc. of the The First World Conference on Organic Seed: Challenges and Opportunities for Organic Agriculture and the Seed Industry, page 184.^*

Summary

Net blotch-infested seeds can be as important as initial inoculum source for net blotch epidemics as other inoculum sources such as infected straw. Our results underline the importance of varietal resistance for seed health. Employing resistant varieties results in low net blotch severity levels in the field which in turn reduces the risk of seed infestation. The results give reason to assume that the present threshold recommendations for seed born barley net blotch could be raised for normal growing conditions and/or for varieties having a reasonable level of net blotch resistance.
Supplemental results are expected from ongoing field trials and more detailed analyses will follow to improve our understanding of quantitative relationships among epidemiological key variables to develop decision support tools for handling net blotch infestations in organic barley seed production.

Additional Summary

Seed born net blotch is a threat to the organic barley seed production in Denmark because it often exceeds the legal 15% infestation threshold in organically produced barley seed lots. Relationships among initial seed infestation levels, disease development during the growing season, yield parameters and net blotch infestation of the harvested grains were examined. Highly significant positive correlations among initial seed infestation, primary infection of seedlings and disease severity during the growing season as well as among disease severity at flowering and infestation of the harvested grains were found. The seed infestation level was much less than proportionally related to the primary infection of seedlings and to the disease severity later in the season. All these variables were negatively correlated with single grain weight, fraction of large grains and total yield. Varietal resistance appeared to be a key determinant for disease severity and seed infestation. The results will be used to help develop more flexible net blotch infestation thresholds for organically produced barley seeds.

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