Seed borne diseases - a challenge for organic cereal production

Anders Borgen and Lars Kristensen

Royal Vet.- and Agricultural University,Dep. Agr. Sci., Agroecology,

Agrovej 10, 2630 Taastrup, Denmark, E-mail: anders@ecoweb.dk

Homepage: http://www.agsci.kvl.dk/agroecology

Keywords: Tilletia tritici, Pyrenophera graminea, plant protection

Introduction

Since the development of mercury seed treatment in 1913, seed borne diseases have been of minor significance in conventional agriculture. In organic agriculture, seed borne diseases are important due to their strong potential for proliferation, limited possibilities for both preventive and direct control measures.

Material and methods

Our research has been a combination of registrations on organic farms, investigations of biology and preventive methods and experiments on direct seed treatments aimed for organic production.

Results and discussion

The systemically infecting seed borne diseases of major importance in Denmark are common bunt in wheat (Tilletia tritici syn. T.caries), leaf stripe disease (Pyrenophera graminea) and loose smut (Ustilago nuda) in barley and stem smut in rye (Urocystis occulta). These diseases are normally considered to be obligate seed borne, but our research has shown that at least common bunt and stem smut can infect a crop from soil resting spores even after several years with non host crops in the field (Borgen 2000, in press). Clean seed lots can be contaminated with common bunt spores from harvest equipment, and our experiments shows that the combine harvester needs to be emptied at least 5 times with clean seeds to avoid contamination (Kristensen et al 1996).

Common bunt in winter wheat and leaf stripe in barley are believed to be the most significant seed borne diseases in Denmark. Preventive methods like isolating the crop from possible inoculum sources with crop rotation in combination with seed analysis has reduced the frequency of these diseases, but has failed to insure an adequate control. 30-50% of all propagated cereal seed-lots in Denmark are at present discarded because of seed borne diseases. We therefore believe that direct seed treatments against these diseases are needed.

Our results shows that common bunt can be effectively controlled by methods like: Hot water treatment at e.g. 55 Cº for 3 minutes, seed dressing with mustard flour at a dose of 10 g/kg grain, seed dressing with acetic acid (1M) at 20 ml/kg grain. A dry physical seed cleaning eg. in a brushing machine can remove up to 99.9% of the bunt spores in a seed lot and may therefore contribute to an intregrated control strategy in combination with other methods. The methods mentioned had only limited side-effects on seed germination properties. Barley leaf stripe can also be controlled by hot water treatment and acetic acid, but acetic acid needs to be further investigated for the optimal dose and concentration. Further, microbiological products and resistant varieties can be expected to contribute to the regulation of seed-borne diseases in the future.

Acetic acid, mustard flour and milk powder are not listed in annex II in the EU standards for organic plant production, and can therefore not be used at present. Microbiological products and also bordeaux liquid and other synthetic fungicides based on copper are listed in the annex II. A principal discussion in the organic movement on the feasibility of the different methods is therefore relevant.

Conclusions

Seed borne diseases are to be considered serious in organic agriculture, and direct seed treatment methods will some times be necessary. Hot water treatment, mustard extracts and acetic acid can provide efficient control methods. Discussions on the feasibility of the different methods in organic agriculture is needed.

References

Borgen, A. (2000). Perennial survival of common bunt (Tilletia tritici) in soil under modern farming practice. Zeitschrift für Pflanzenkrankheiten und Pflanzenschutz. in press

Borgen, A. and M.Davanlou (2000). Biological control of common bunt (Tilletia tritici) in organic farming. Journal of Plant Production. in press

Kristensen, L, A. Borgen og P.Kølster (1996). Stinkbrandspores spredning via mejetærskere.13. Danish Plant Protection Conference. SP-rapport 4:185-192