Understanding the physiological disorders in daffodil - BOF 076 project extension to study the three-year-down crop

Daffodil rust (physiological rust or stem rust) makes stems unmarketable, causing financial losses and potentially a loss of markets. The cause of rust is unknown. Pathological or nutritional causes have been tentatively ruled out, and an environmental cause (such as adverse soil/water conditions) suggested instead.
BOF 76 is investigating the associations between rust, soil/water and other factors over two years. Plots of daffodil ‘Golden Ducat’ were planted in ten locations in Cornwall and soil/water and other factors recorded. In year 1 a variable but low level of rust was found at all sites, with a higher incidence at three of four sites having high soil water content. Year 2 is underway and the incidence and severity of rust are greater than before though not severe.
The sporadic nature of rust, the view that it is not generally significant in crops in their first year, and the relatively low levels found so far, confirm the value of extending the project to cover the whole three-year growing period typically used. This proposal is to fund a third-year extension using the plots and monitoring equipment already in place.

 

Daffodil rust occurs sporadically, but (on the basis of information provided by growers as part of BOF 76) results in a 3% average annual loss of revenue (spread across all years) or losses of 10% in one year in three (with negligible losses in the intervening years). Currently a 3% annual loss would amount to about £0.7m annually for UK growers, or around £2.3m every three years. These figures represent only the direct monetary losses from reduced flower sales and returns, and there are additional costs associated with managing unpredictable yields.
With commercial daffodil growing in the UK more dependent on the sales of cut-flowers than bulbs, it is vital to avoid anything which could harm the buyers’ perception of the quality of the UK product. Ongoing problems with daffodil rust could result in a substantial loss of markets.
These losses could be largely eliminated if the project succeeds in identifying the cause of daffodil rust and is able to propound treatments, avoidance strategies and risk management opportunities that avoid rust development. The findings would be delivered through the normal channels of seminars, news articles and a fact-sheet.

(i) Project aim(s):

To identify the cause of daffodil rust

(ii) Project objective(s):

1 Extend the current two-year project to a third year in order to complete observations on the existing trial plots over the typical three-year-down growing cycle used in daffodil growing:
1.1 Complete observations on the effect of the soil/water environment and related factors on the incidence and severity of daffodil rust
1.2 Obtain further analyses of nutrients in soil and plant tissue associated with rust-affected and ‘healthy’ plots
1.3 Continue pathogen testing of rust-affected and ‘healthy’ stems

2 Investigate any association of daffodil rust with virus infection by RNA extraction and sequencing of rust-affected and ‘healthy’ stem tissue, using samples previously collected in the project and stored at -70°C

3 Determine the earliest date that daffodil rust symptoms appear by examining the above- and below-ground parts of stems at intervals from before bulb sprouting until flowering; this will inform us on the time-scale of rust development

4 Survey commercial cut-flower samples to discover whether mild daffodil rust symptoms are ubiquitous in a rust-prone and a non-rust-prone cultivar; this is basic information that will help us understand daffodil rust

5 Build on the results of the original project to inform the daffodil industry on the cause of daffodil rust and assist in formulating a protocol for its control through remedial treatments, avoidance strategies and risk management opportunities, using presentations at grower meetings, articles and a fact-sheet; if appropriate, facilitate discussions with science specialists on further research needs

Together, objectives 1 and 5 form a package. This package and objectives 2 to 4 are not interdependent, but much more would be added to our understanding of daffodil rust if all objectives were included.

The project extension would be based on work carried out in one year, and the overall project would be based on studying a single three-year crop cycle in one region of the UK, so it is possible the findings may not be truly representative because of weather, local factors or year-to-year variation.

Conditions beyond the contractor’s control, such as unusual weather, serious pest or disease problems, or material changes within the bulb industry, could affect the process of obtaining representative results. The sporadic nature of daffodil rust means that in some years the disorder is absent or occurs at a very low level.