Contans first biocontrol agent against Sclerotinia sclerotiorum in oilseed rape

 

Katrin Hedke 1, Peter Lth 2, Andreas von Tiedemann 1

 

1 University of Rostock, Faculty of Agriculture, Department of Phytomedicine, Satower

Strasse 48, Rostock D-18051, Germany

e-mail: katrin.hedke@agrarfak.uni-rostock.de

2 Prophyta Biologischer Pflanzenschutz GmbH, Inselstrasse 12, Malchow/Poel D-23999, Germany

e-mail: prophyta@t-online.de

 

Abstract

 

The biocontrol agent Contans is based on conidia of the soil fungus Coniothyrium minitans, a mycoparasite of Sclerotinia sclerotiorum. It has been registered for use in oilseed rape and vegetables in Germany.

Results of two-year field trials conducted on three farms in Northern Germany are presented. The aim was to introduce Contans for biocontrol of S. sclerotiorum in commercial oilseed rape production and to evaluate the practicability and efficacy of different treatments. The biocontrol agent was tested with respect to timing, dose and frequency of application in combination with conventional or reduced tillage. The field trials showed good efficacy of Contans with disease reductions of up to 60 % in the first year and additional long term effects. With regard to autumn applications, different variants of timing showed a good flexibility and high practicability of the procedure. The dose of 1 kg Contans per hectare (1x1012 viable spores) seems to be sufficient to achieve satisfactory disease control.

 

Keywords: Coniothyrium minitans, biological fungicide, sclerotia, mycoparasitism, soil

application

 

Introduction

 

Coniothyrium minitans Campbell is a comparably well-known mycoparasite of sclerotia. Since its first isolation from sclerotia of Sclerotinia sclerotiorum Lib. de Bary in 1947 the antagonist has been found in many soils worldwide and on several kinds of ascomycetous sclerotia-forming fungi (Whipps and Gerlagh 1992, Sandys-Winsch et al. 1993). C. minitans is parasitic on and destroys the sclerotia of S. sclerotiorum thereby reducing airborne ascospore infections of the pathogen. This specific ability leads to a new strategy of plant protection concerning Sclerotinia diseases which is of special interest in oilseed rape. In contrast to the usual spray at flowering stage to prevent ascospore infections, an application of the biocontrol agent directly onto the soil aims at destructing the duration bodies of S. sclerotiorum, in this way achieving a soil decontamination.

 

So far, results of soil treatments in the greenhouse have been very promising. There have also been first tests in different field-grown crops including host and non-host crops (McLaren and Huang 1996). Preliminary tests in microplots of oilseed rape proved a reduction of soil inoculum but this neither lead to disease control nor to a yield improvement (McQuilken et al. 1995). The reasons for this are generally attributed to the fact that Sclerotinia ascospores dispersal occurs over long distances (Lefol and Morrall 1997) and thus strongly affect adjacent plots. In the study presented here, results of two years of field trials in commercial grown oilseed rape are outlined. To eliminate falsifications due to ascospore dissemination between treatments, our experimental design is based on macroplots surrounded by guard areas to prevent major influences of invading external ascopores.

 

Experimental

 

Production procedure and characteristics of the biocontrol agent

 

The biofungicide Contans consists of the dried conidia of the sclerotia pathogenic fungus Coniothyrium minitans. The product is formulated using glucose as carrier for the conidia. One kilogram of the product contains 1 x 1012 living conidia. This corresponds to 53 g dry mass in ratio to 947 g glucose. The product has to be dissolved in water, sprayed onto the soil surface and incorporated into the soil.

 

A solid-state fermentation technique is used for the production of the fungal conidia. With the help of this technique it is possible to produce 4 x 109 conidia per g culture substrate. These conidia are harvested from the culture substrate with a special micro-screening method. The result of this step of the production chain is a pure conidia suspension. This suspension is used in a fluidized bed drying procedure to produce the end product. The use of a pure conidia suspension ensures very high purity of the end product. Most other products which are manufactured on the basis of an antagonistic fungus consist of spores or conidia, mycelium and residues of the culture substrate. It is therefore very difficult to determine the real content of colony forming units in such products. Very often microbial fungicides are also contaminated with other undesirable fungi.

 

Since Contans is a highly active microbiological agent that specifically attacks the sclerotia in the soil, there are no adverse effects on the soil ecosystem in general. In addition, there are no toxic or allergic effects on mammals, fish or insects known. The necessary toxicological and eco-toxicological investigations have been carried out. The fungus C. minitans does not grow at a temperature above 35 C which excludes any disease in mammals.

 

At present, the product is registered in Germany for oilseed rape and lettuce and in Switzerland for lettuce, cucumber and beans.

 

Field trials in oilseed rape

 

Field trials were initiated in 1997 at three locations in Northern Germany to introduce Contans for biocontrol of S. sclerotiorum in commercial winter oilseed rape production and to evaluate the practicability and efficiency of different treatments. The biocontrol agent is tested with respect to timing, dose and frequency of application in combination with conventional or reduced tillage at sites with high Sclerotina infestation. To minimize the effects of ascospores dispersed between plots, macroplots of a size of 54 x 40 m are uniformly treated and only the centre area is used for evaluations. An edge of 15 m in each direction is established as a guard area to reduce effects of travelling ascospores. This results in a total size of about 6 ha per trial at one location. To evaluate long-term effects, the plots are situated identical every year in an oilseed rape monoculture.

 

The compared biocontrol systems concentrate on autumn soil applications which proved to be more effective than spring applications (McQuilken et al. 1995) and are easy to integrate into a cropping management system. Contans is applied directly onto the soil and incorporated by the following cultivation. The variants are listed in table 1. Treatments with the antagonist are compared to an untreated control, a treatment with a synthetic fungicide at flowering stage (Konker R, 1.5 l ha-1) and treatments with combinations of a repeated autumn application with Contans followed by a leaf spray with the synthetic fungicide at flowering stage.

Table 1: Factors of the field trials in commercial grown oilseed rape.

Timing of Contans application

a-

post-harvest,

(directly onto the stubble)

 

b-

pre-sowing

(after ploughing/reduced tillage)

 

 

 

 

Tillage system in combination with

a-

conventional

(plough)

different application times

b-

reduced

(grubber)

 

 

 

 

Dose of Contans

a-

1 kg ha-1

(1 * 1012 viable spores ha-1)

 

b-

2 kg ha-1

(2 * 1012 viable spores ha-1)

 

 

 

 

Frequency of application over the years

a-

yearly

 

 

b-

every two years

 

 

 

 

 

 

Disease assessments are made three times in three-week intervals from growth stage 69 to 87. Incidence, severity and location of infections of S. sclerotiorum are determined. After harvest, stubble samples are taken to score the incidence of myceliogenic (root-)infections. Plant disease assessments are accompanied by investigations with the help of baiting sclerotia - incorporated in autumn and analyzed in the following spring -, by soil sampling in spring to reisolate the antagonist from soil and yield analysis.

 

In 1998, reduced tillage already showed a strong effect on disease development of S. sclerotiorum. In untreated controls disease developed more rapidly and reached higher final incidences in non-ploughed than in conventionally tilled oilseed rape plots. On average of the three locations, final disease levels reached 40.0 % in ploughed compared to 49.1 % in non-ploughed plots at growth stage 85/87.

 

The relative disease reduction by a single Contans treatment at the last time of disease assessment was 49.8 % on average of all variants. Disease reductions ranged from 29.4 % (reduced tillage, 79.3 % Sclerotinia disease incidence in the untreated control) to 65.8 % (ploughing, 28.7 % disease incidence in the untreated control). Crops with reduced tillage and high disease levels showed comparably less effect of a treatment with Contans at this final stage but a slower disease development at the beginning. Due to myceliogenic spread of infections between upper plant parts during the whole wet season disease increased continuously until the end of the vegetation period.

 

Final disease levels were comparably similar regardless of the application time. Post-harvest and pre-sowing applications led to disease levels of about 9.5 % incidence of S. sclerotiorum in systems with conventional ploughing and 19.5 % in systems with reduced tillage at locations with medium disease levels (untreated control values: 26.4 % and 34 % respectively). Only at one location with extreme disease pressure the efficacy of the biocontrol agent in the first year was not satisfactory. Incidences of 73.3 % Sclerotinia disease were reduced to 43.2 % but this would call for additional fungicide strategies at least in the first year. Long-term effects will be of special interest at this location and will be outlined during the following season. No difference could be determined between the effects of the doses 1 or 2 kg ha-1 Contans. So far the application of only 1 kg ha-1 seems to be sufficient.

 

Conclusions

Contans is the first biological fungicide that can be used economically in low value agricultural crops like oilseed rape. This is possible because the production costs are relatively low in comparison with other biocontrol agents. In this context the development of an application system in oilseed rape fulfills the function of a precedent of applications in other field-grown crops. Our aim is to get the product registered for all susceptible crops world-wide.

 

The results of the field trials in oilseed rape so far indicate that C. minitans can be handled with flexibility allowing users to implement the plant protection strategy into existing cropping systems. Glasshouse trials also prove that the antagonist is effective under a comparably wide range of temperature and soil humidity conditions (Hedke and Tiedemann 1998). Very often, the use of biocontrol agents is restricted to controlled environments in the greenhouse because they need stable environmental conditions (Whipps 1994) but C. minitans seems to be active under a wide range of conditions. This implies promising perspectives for the use of the antagonist not only in horticultural but also in high-acreage field-grown crops. The trials in oilseed rape are continued to optimize the biological plant protection strategy. We also hope to prove the biocontrol agent's potential to achieve long-term effects as already indicated in other studies (McLaren et al. 1994, McQuilken et al. 1995). This might lead to an effective soil decontamination.

 

Acknowledgements

The authors wish to thank U.Eiben for skillful technical assistance in developing the actual product as well as the cooperating farmers and Dr.R.Mgling, H.Puff, M.Goltermann and I.Gliege for intensive technical support in performing the field trials.

 

References

Hedke, K., Tiedemann, A.v. 1998. Environmental influences on the decomposition of sclerotia of Sclerotinia sclerotiorum by Coniothyrium minitans. Mitteilungen aus der Biologischen Bundesanstalt 357, 352.

 

Lefol, C., Morrall, R. A. A. 1997. Dispersal of ascospores of Sclerotinia sclerotiorum in canopies of flowering canola. Canadian Journal of Plant Pathology 19, 113.

 

McLaren, D.L., Huang, H.C., Kozub, G.C., Rimmer, S.R. 1994. Biological control of Sclerotinia wilt of sunflower with Talaromyces flavus and Coniothyrium minitans. Plant Disease 78, 231-235.

 

McLaren, D.L., Huang, H.C., Rimmer, S.R. 1996. Control of apothecial production of Sclerotinia sclerotiorum by Coniothyrium minitans and Talaromyces flavus. Plant Disease 80, 1373-1378.

 

McQuilken, M.P., Mitchell, S.J., Budge, S.P., Whipps, J.M., Fenlon, J.S., Archer, S.A. 1995. Effect of Coniothyrium minitans on sclerotial survival and apothecial production of Sclerotinia sclerotiorum in field-grown oilseed rape. Plant Pathology 44, 883-896.

 

Sandys-Winsch, D.C., Whipps, J.M., Gerlagh, M., Kruse, M. 1993. World distribution of the sclerotial mycoparasite Coniothyrium minitans. Mycological Research 97:1175-1178.

 

Whipps, J.M., Gerlagh, M. 1992. Biology of Coniothyrium minitans and its potential for use in disease biocontrol. Mycological Research 96, 897-907.

 

Whipps, J.M. 1994. Advances in biological control in protected crops. Brighton Crop Protection Conference, Pests and Diseases 1994, 1259-1264.