Soil-borne plant diseases are a serious impediment in organic crop production. Several species within the plant family Brassicaceae are very important potential sanitisers of plant pathogens that can survive in the soil. Oilseed radish (Raphanus sativus ssp. oleifera), white mustard (Sinapis alba) and oriental or Indian mustard (Brassica juncea) are the main focus of interest. In addition to being disease sanitisers, these intercrops are also catch crops, green manure crops and structure improvers.
Oilseed radish and mustard
Disease saniters with great potential
Project manager: Paula Persson, Department of Crop Production Ecology, SLU
International literature shows that a number of pathogenic fungi, but also certain nematodes, can be inhibited by incorporation into the soil of biomass of oilseed radish and/or mustard. The mechanisms behind this inhibition have not been determined for each individual case, but one of the effects is conversion of the glucosinolates in the brassicas into isothiocyanates. It is extremely important that the biomass is thoroughly chopped and incorporated immediately.
- The main hypotheses of this project are:
Chopping and incorporation of the biomass of an intercrop with a high glucosinolate content has a sanitising effect against soil-borne plant pathogens
- The mechanisms behind this inhibition are either immediate conversion of glucosinolate into isothiocyanate or an indirect action as a result of transformations in the composition of the soil flora.
In this project we will be working with brassica intercrops containing high but also low concentrations of glucosinolates. We have decided to study four economically important diseases and the pathogens responsible:
- Pea root rot (Aphanomyces euteiches);
- potato spraing (tobacco rattle virus, TRV);
- stem canker (Rhizoctonia solani) and
- white rot (Sclerotinia sclerotiorum).
We will grow the intercrops outdoors in large crates and incorporate the biomass at early flowering, add known amounts of pathogens at sowing and analyse any inhibition using biotests and DNA-based analytical methods. The effects of the crop on structure of the soil microflora will be analysed through DNA extraction of soil samples before and after biomass incorporation. The DNA in the soil samples will be analysed using e.g. T-RFLP, which gives the sample a DNA fingerprint and can therefore reveal changes in structure.
Didon UME, Widmark D, Soldevilla-Martinez M, Kolseth AK & Persson P, 2009. Allelopathic Cover Crops – Effects on Plant Pathogens and Weeds. Proceedings of the 1st Nordic Organic Conference. Towards increased sustainability in the food supply chain. Göteborg 18-20 May 2009, p. 157