Evaluating potential new fungicides for the control of Narcissus basal rot in bulb and plant tests

Project summary:

UK Narcissus growers rely on two fungicide active ingredients (a.i.) for the control of basal rot caused by Fusarium oxysporum f.sp. narcissi (FON), the most serious pathogen affecting Narcissus crops. These are chlorothalonil and thiabendazole both of which are available for dipping bulbs (including hot-water treatment, HWT) through EAMUs. This situation leaves the industry vulnerable to a loss of disease control options as a result of legislation or commercial considerations.

To address this, HDC project BOF 74 was commissioned in 2011 to identify new fungicides which could suppress the growth of FON isolates on agar in vitro. Products based on prochloraz (an imidazole), tebuconazole (a triazole) or copper oxychloride were found to be most effective at suppressing FON growth. Results for the currently approved fungicides chlorothalonil and thiabendazole showed that the former was relatively ineffective except at the higher concentrations, while the latter failed to adequately reduce growth of two of the eight FON isolates tested, suggesting pathogen tolerance to this a.i.

In this project we will test the efficacy of prochloraz and tebuconazole against FON in plant tests before expensive commercial on-farm trials are conducted and potential EAMUs progressed. Copper oxychloride will not be tested as it was found in BOF74 that relatively high concentrations were required for activity against FON. However, this product may still be examined in the future. In addition, we will test FON isolates against other triazoles and imidazoles given that these classes of fungicides have slightly different modes of action and appear to have good activity so that additional backup products are potentially identified for future approval. The main experimental focus of the project will therefore be to evaluate the efficacy of prochloraz and tebuconazole against FON using small-scale HWT in plant/bulb tests under controlled conditions where basal rot development can be ensured, and to compare the results with the current industry standards thiabendazole and chlorothalonil. Both curative and protectant activity (a key factor not previously addressed in this plant/disease combination) will be assessed. A biological control agent will also be tested and hence a range of basal rot control options will be compared and potential phytotoxic or growth promoting effects of all the treatments assessed. At the end of the project, the results of this and related work will be synthesised to devise a robust integrated control strategy for Narcissus basal rot that will reduce the risk of fungicide resistance and explore different control options. Recommendations for follow-up on-farm field trials will also be made.

Benefits to industry:

The UK daffodil industry is estimated to be worth about £45m per annum and with significant dependence on the high-quality export and multiple-retailer markets, daffodil bulb and flower production is vulnerable to loss of yield and quality as a result of basal rot and other factors. Having more options for managing basal rot is therefore a key factor in ensuring the survival of the industry.

The results of this project will build on those of BOF74 to identify new products and control options against Narcissus basal rot that can be taken forward to registration and field trials under commercial conditions. These control options will be based on rigorous experimental evidence based both on in vitro and in planta experiments with activity of fungicides demonstrated across a broad range of FON isolates. The project will hence provide good evidence for the best treatments to take forward in an integrated control strategy. The use of small-scale HWT and the testing of potential new treatments in glasshouse trials is an essential step before considering investing time and money in evaluating new products in commercial-scale HWT dips, field experiments and seeking approvals through EAMUs. A small scale HWT set-up also overcomes the problems of disposing of large volumes of fungicides. The project is therefore a major step towards alleviating the dependence of the industry on thiabendazole and chlorothalonil (following the necessary approvals). This is particularly desirable as results from BOF 74 showed that chlorothalonil was less effective than other fungicides and that a quarter of the FON isolates tested exhibited tolerance to thiabendazole, which is also regarded as expensive and has some strict limitations on its use.

The industry will also benefit from the expertise and knowledge being built-up by researchers at Warwick Crop Centre working on Fusarium oxysporum f.sp. cepae (basal rot of onion) and other formae speciales, which can be applied to the Narcissus crop. Areas of research at Warwick include screening for plant resistance, identification, detection, diversity and genetic basis for pathogenicity of F. oxysporum as well as biological control using microbial products. Work on biological control originally started at Warwick and has been continued more recently through Ralph Noble (EMR; BOF 69). As well as expertise, a large culture collection of FON isolates (some of which are molecularly characterised) will remain available for future research. This proposal will also necessarily involve setting up a small-scale HWT facility which is not currently available elsewhere. Although there is some expense associated with this, it would remain a future asset for HWT research. There is therefore a significant centre for Fusarium research at Warwick and it is hoped that this can continue to be exploited for the benefit of UK Narcissus growers. All these benefits would be communicated to the industry through the usual means of an article in HDC News, a fact-sheet, a talk to growers or an Open Day, and a final report.