Brassicas: Evaluating the use of novel biocides for the control of Xanthomonas campestris pv. campestris in modules during propagation.

• A number of horticultural disinfectant products along with Thyme oil and a bio-control product were tested in the laboratory to investigate their efficacy in inhibiting the growth of Xanthomonas campestris pv. campestris (Xcc) in an in vitro experiment.
• All products performed well, particularly at the higher concentrations and inhibited the growth of Xcc at a range of different time exposures.
• ‘Sanogene’ (chlorine dioxide) proved to be the most effective of all the products tested, with ‘Sporekill’ (didecyl dimethyl ammonium dioxide) proving only slightly less effective. Thyme oil and Jet 5 (per-acetic acid) were effective, though marginally less so than the two products named previously.
• The biological control product – ‘Serenade’ (Bacillus subtilis) could not be tested in the same way as the other products as its mode of action involves direct competition with Xcc in terms of nutrients, niches and the possible release of secondary (inhibitory) metabolites. The modified experiments showed that at the higher concentrations there was clear inhibition of Xcc in culture. However, whilst a qualitative effect was found, it was not possible to quantify it effectively in an in vitrotest and hence form a clear idea of the potential efficacy of this product. It is therefore recommended that further work is undertaken with this product in vivo.

A number of horticultural disinfectant products, a plant oil and a bio-control product were evaluated in vitro and found to be effective against Xanthomonas campestris pv. campestris, cause of black rot of crucifers, in laboratory studies. Chlorine dioxide (‘Sanogene’) and didecyl dimethyl ammonium chloride (‘Sporekill’) were found to be most effective in this initial in vitro test.

Background and expected deliverables:

The seed-borne pathogen Xanthomonas campestris pv. Campestris (Xcc.) causes black rot in Brassica seedlings during propagation. It has been estimated that even very low seedborne infections e.g.<1 in 10,000 seed can lead to epidemic development of the disease in intensive monoculture systems such as Brassica propagation. There has been discussion in the industry that products such as Jet 5/Hyperox are becoming less effective in controlling the spread of infection from primary infector plants (R White : pers. comm.). This investigation focused on looking at the efficacy of possible alternative products for use in the future.

Information regarding one possible candidate product for this work was put forward by a prominent Brassica propagator. The product - ‘Sporekill’™ is marketed as ‘a horticultural disinfectant and plant sanitiser’. However, at present this product is not registered for use in the UK though is currently marketed in South Africa and Australia. This product, whose active ingredient is didecy dimethyl ammonium chloride, was tested alongside ‘Jet 5’(hydrogen peroxide/per-acetic acid), ‘Sanogene’ (chlorine dioxide), Thyme Oil and the biological control product ‘Serenade’ (Bacillus subtilis) in an in vitro study to ascertain their relative efficacy in inhibiting the growth of Xcc.

It was hoped that this small-scale laboratory experiment would provide some initial comparative data to enable the propagation industry to make decisions regarding the potential for further study to ultimately gain improved control of black rot in Brassica seedlings and, ultimately, crops post-planting.