Efficacy of CONTANS®WG for the control of sclerotinia rot in carrot: A case study for other susceptible muck soil crops

Project Code : BPI06-190

Project Lead

Vicky Toussaint - Agriculture and Agri-Food Canada.

Objective

To determine the potential of biofungicide Contans®WG, a commercial formulation of the mycoparasite Coniothyrium minitans, to control Sclerotinia rot in carrots grown in muck soil.

Summary of Results

White mould caused by Sclerotinia sclerotiorum, is an important disease of carrots crop and is a major concern of the carrot industry in the eastern part of Canada. At the beginning of this project in 2006, no fungicide was registered to control this disease in carrots. Moreover, using a chemical during the growing season is complicated since the sclerotia (primary inoculum) are buried in the soil or well protected by carrot canopy. Contans®WG, a commercial formulation of Coniothyrium minitans, is known for its capacity to reduce damage caused by S. sclerotiorum in several crops by infecting and degrading sclerotia in the soil. However, most of studies were conducted under loam type soils. Very few data were available for its efficacy in muck soil, a widespread soil type used for horticultural crops in Quebec and Ontario. The biology, structure and physical/chemical properties of this soil are very different from sandy or clay loams. Hence, no conclusion could be drawn on the efficacy of the biocontrol in muck soil. The goal of this project was to assess the efficacy of Contans®WG, in terms of potential survival and ability to infect and degrade S. sclerotiorum sclerotia in muck soil. These assessments were validated in both field and laboratory conditions and compared with the efficacy in mineral soil.

Under field conditions, Contans®WG was applied at rates of 4.5 and 9 kg/ha and either drench-incorporated (spring 2006) or mechanically incorporated (spring 2007). In 2006, Contans®WG did not appear to suppress emergence of apothecia of S. sclerotiorum nor the development of white rot in storage. It was assumed that this was in part caused by the limited contact between S. sclerotiorum sclerotia and the hyperparasite C. minitans when Contans®WG was applied using a drench incorporation technique. This hypothesis was supported by the fact that sclerotia treated in a similar method (4.5 and 9 kg/ha of Contans®WG) and exposed to the same weather conditions, but placed in mesh bags and buried in corresponding plots were destroyed. In 2007, the number of apothecia observed was lower compared to 2006, including for the control, due to high temperatures observed during the growing season. Apothecia emerged in mid-September, and were observed in all treatments, but Contans®WG treatments were not significantly different from the control for the number of apothecia in the experimental plots and the disease incidence in storage. It should be emphasized that in both years of the study, the weather conditions during the growing season (moisture and temperature) were not conducive to disease development.

Results obtained in laboratory trials comparing the efficacy of Contans®WG in organic versus mineral soil, suggest that: i) under controlled conditions (20°C) and at water tensions between  -7 and -15 kPa, the activity of C. minitans is similar in both types of soil; ii) conditions that maximize contact between C. minitans and S. sclerotiorum will increase the efficacy of the biocontrol; iii) waterlogged soil conditions (-1 kPa) limit the activity of the C. minitans. These observations contribute to a better understanding of how to optimize field conditions that favour C. minitans activity in soil. Some recommendations drown from this study include using shallow tillage to incorporate Contans®WG, good drainage and limiting surface irrigation. The study of growth and sporulation of C. minitans on water agar soil amended media revealed that fungal growth is superior on mineral than on organic amended media. Moreover, an increase of the organic fraction will have a negative effect on vegetative growth but a stimulatory effect on C. minitans sporulation. This study validates the efficacy of C. minitans (Contans®WG) to degrade S. sclerotiorum sclerotia in both mineral and muck soil types under controlled conditions, but its efficacy in the field still needs to be established.

For more information about this project please contact Dr. Vicky Toussaint

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