BIOLOGICAL SEED TREATMENT

Karin Förster, Monika Pfannmöller, Wulf Diepenbrock

Institute of Agronomy and Crop Science, Martin-Luther-University Halle-Wittenberg, Germany

Abstract

In Germany no biological seed dressings are licensed, but some plant stimulating products with additional effects on pathogens are known. Plant extracts against seed borne diseases are under investigation. Comparing with recent developments in technology of thermal or electron seed treatment biological alternatives are not well developed. There are different problems with biological seed treatment. One is the handling, if microorganisms are used. Another is connected with the standardisation of plant extracts and their lower efficacy comparing with chemical seed treatment.

A certain amount of plants, natural products and microorganisms had been found to have inhibitory effects on plant pathogens. The importance of alternative products increases especially for organic farming and therefore the need to develop practicable solutions for biological seed treatment.

biological seed treatment, organic farming, soil-borne diseases, seed-borne diseases

Souhrn

V Německu nejsou povoleny žádné biologické přípravky k ošetření semen, ale jsou známy některé rostlinné stimulující produkty s vedlejšími vlivy na patogeny. Zkoumají se rostlinné extrakty působící proti chorobám přenosných osivem. Srovnání biologických možností se současným vývojem technologie tepelného nebo elektronového ošetření semen není řádně rozvíjeno. S biologickým ošetřením semen se vyskytují různé problémy. Jedním z nich je manipulace s mikroorganismy. Další je spojován se standardizací rostlinných extraktů a jejich nižší účinností ve srovnání s chemickým ošetřením semen.

Určité množství rostlin, přírodních produktů a mikroorganismů má inhibiční efekt na patogeny. Významnost alternativních produktů se zvýší zvláště z hlediska ekologického zemědělství a proto je třeba rozvíjet praktická řešení biologického ošetření semen.

Introduction

One of the most important problems of seed multiplication is the production of healthy seeds. Closed crop rotations, changing climatic conditions, changes in the distribution and activity of pathogens resulted in seeds which can be more or less infected with seed-borne diseases or noxious insects. Seed-borne organisms (fungi, viruses and bacteria) are wide distributed and can affect seed quality, especially germination and field emergence.

The seed certification system guarantees the health of certified untreated seed or certified treated seed respectively. In some cases the quality level for seed certification can only be reached with chemical treated seed.

Seed treatment based on chemical substances can protect seed against different forms of seed-borne, soil-borne or wind-borne diseases as well as other pests. In integrated agriculture the most common used form of seed treatment is the chemical one. Alternative forms of disease control e.g. physical or biological seed treatment are of lower importance.

In organic farming the use of the most chemicals is not allowed, that´s why alternative principles and techniques for seed treatment are necessary. The physical seed treatment is pushed through new developments on thermal treatment of cereal and vegetable seed or electron seed treatment (Schröder et al. 1998). Another very interesting alternative form of seed treatment is the biological seed protection. Biological seed treatment developed into three directions: use of antagonists, biopriming and use of natural plants or plant extracts inhibiting pathogen growth orkilling pathogens.

In the following some aspects about the situation of seed treatment with biological active microorganisms or natural plant extracts against soil-borne and seed-borne diseases in Germany are discussed.

Beside seed inoculation with microorganisms which are beneficial to plant growth, particularly rhizobial bacteria, seed treatment has been directed against soil-borne pests. Bio-protectants, fungi and bacteria providing short-term protection against seed rot and damping-off fungi (e.g. Pythium spp.) are known as effective systems (Maude 1996).

Principles of microbial seed treatment against damping off fungi are well studied for sugar beet. The influence of environmental factors and dosage effects on effectiveness of seed treatment are of special interest. So, Schmidt et al. (2000a) reported results from three biocontrol agents Pseudomonas fluorescens, Pseudomonas corrugata and Bacillus subtilis against Pythium damping. Soil pH did not have any influence on biocontrol activity of the agents. In further phytotron experiments Schmidt et al. (2000b) studied the influence of increasing Pseudomonas fluorescens and Pseudomonas corrugata doses on antagonistic performance in seed pellets. Under the condition of pelleting both Pseudomonas strains were able to persist and to propagate on the seedling surfaces. But Tilcher et al. (2000) considered that the potential of antagonistic microorganisms for sugar beet seed treatment is not yet big enough to commercialise sugar beet pellets free of fungicides. The formulation of antagonists as well as the pelleting process have to be optimised and the screening of isolates which can be used for sugar beet pellet production should be continued.

Experiments of Marten et al. (2000) showed that a treatment of sugar beet seeds with Rhizovit 7 (Streptomyces isolate) was very effective. The emergence rate of treated sugar beet seed pellets in soils which were inoculated with Rhizoctonia solani and Pythium ultimum was significant better in comparison with the untreated control. After seed infiltration with the Streptomyces preparation good biocontrol results were found in the systems Valeriana locusta / Phoma valerianellae and Valeriana locusta /Alternaria species.

In Germany no biological seed dressing against soil-borne fungi is licensed up to now. But with CONTANS WG (Coniothyrium minitans) the first biological fungicide is listed in the Register of Authorised Plant Protection Products. It can be used for direct soil treatment against sclerotia of Sclerotinia sclerotiorum and other sclerotial fungi (BBA 2000).

Control of seed-borne pathogens

The use of microbial antagonists or natural plant extracts for the control of seed-borne diseases on cereals or vegetables is not well investigated up to now. One reason is the high efficacy of chemical seed treatment.

The organic farming can not use seed treatment with synthetic substances. Seed-borne pathogens like Tilletia spp., Fusarium spp., Ustilago spp. and so on lead to increased disease levels and to yield losses in organic farming. Therefore alternative strategies are very important. Natural products like milk powder or dextrose as well as inorganic materials, microbial antagonists and biopriming, a combination of biological seed treatment with bacteria and preplant hydration, are described as such alternative treatments.

Spieß and Dutschke (1992) used different plants like mustard, horse-radish, alfalfa, garlic, algae and also liquid manure as biological agents for wheat seed treatment against Tilletia caries. They found a high effectiveness of these materials ranging from 91 to 99.8 %.

Results of Koch and Lindner (2000) about the use of different bacterial antagonists against Fusarium graminearum, F. culmorum and Microdochium nivale show an inhibition of the mycelial growth especially of F. culmorum and M. nivale in laboratory tests. Field emergence and the number of plants after winter increased.

In vegetable production biological plant protection is also very important. Therefore effectiveness of bacterial antagonists as well as electron seed treatment and a combination of both against seed-borne and soil-borne pathogens are tested. Jahn and Puls (1998) used essentially the host/pathogen combinations Daucus carota / Alternaria spp. and Brassica oleracea / Xanthomonas campestris. They tested 4 Pseudomonas strains and 5 Bacillus strains as bacterial antagonists against the soil-borne pathogens Pythium ultimum and Rhizoctonia solani. The combination of electron and bacterial seed treatment was not so efficient as the electron seed treatment combined with the direct soil application of the bacteria.

The control of plant pathogens through treatments with defined plant extracts is more and more under investigation. Table 1 summarises some patent applications.

Table 1: Patent applications concerning plant extracts with fungicidal effects

Out of a lot of references concerning fungal growth inhibition or fungicidal and bactericidal effects of natural materials mosses seem to be of interest. In agar tests moss extracts inhibit fungal and bacterial growth (Frahm 2000). Their potential for the control of seed-borne diseases is not yet investigated.

In Germany beside common plant protection products, simple products on natural basis to be prepared by the farmer, and plant health (and growth) stimulating products on natural basis are known. For the purposes of organic farming a special list of applicable products is available.

One of the products for plant protection with the aim to stimulate the plant growth is Tillecur 7 (Gebr. Schaette KG, Bad Waldsee), which is also effective against Tilletia species. Tillecur is a mustard and horse-radish preparation. The resistance inducing product ComCat 7 (Polus GmbH, Lindenfels) is based on plant extracts. As active compounds Schnabl and Polus (1999) isolated brassinosteroids among others.

References

BBA 2000: Pflanzenschutzmittelverzeichnis, Teil 1. Biologische Bundesanstalt für Land- und Forstwirtschaft Braunschweig

Frahm, J.-P. 2000: Moosextrakte gegen Pilzbefall. Innovation 4, 22-23.

Jahn, M. and Puls, A. 1998: Zur Wirkung von Elektronenbehandlung und bakteriellen Antago-nisten gegen samen- und bodenbürtige Krankheitserreger an ausgewählten Gemüsekulturen. Mitt. BBA 357, 442-443.

Koch, E., Lindner, K. 2000: Möglichkeiten der Bekämpfung samenbürtiger Krankheiten an Getreide mit mikrobiellen Antagonisten. Mitt. BBA, 376, 192.

Marten, P., Minkwitz, A., Brückner, S., Lüth, P., Berg, G. 2000: Biologische Kontrolle pflanzenpathogener Pilze mit Rhizovit 7 auf der Basis von Streptomyces spec. DSMZ 12424. Mitt. BBA, 376, 573.

Maude, R. B. 1996: Seedborne diseases and their control. Principles and practice. CAB International Wallingford

Schmidt, C.S., Agostini, F., Whyte, J., Simon, A.M., Mullins, C.M., Leifert, C. 2000a: Influence of soil pH, soil temperature and soil type on biocontrol of Pythium damping off disease by antagonistic bacteria. Mitt. BBA, 376, 566.

Schmidt, C.S., Agostini, F., Mullins, C.M., Leifert, C. 2000b: Influence of initial antagonist dose on sugar beet root colonisation and biocontrol of Pythium damping off. Mitt. BBA, 376, 566.

Schnabl, H., Polus, G. 1999: Biological plant protection agent with resistance-promoting action and method for producing same. Patent application WO 99/38379.

Schröder, T., Röder, O., Lindner, K. 1998: e-dressing - a unique technology for seed. ISTA News Bulletin 118, 13-15.

Spieß, H., Dutschke, J. 1992: Bekämpfung des Weizensteinbrandes (Tilletia caries). Ökologie und Landbau 81, 7-9.

Tilcher, R., Peter, B.-F., Krebs, B. 2000: Behandlung von Zuckerrüben-Saatgut mit mikro-biellen Antagonisten. Mitt. BBA, 376, 421.