The epidemiology and control of heuchera rust


HNS 191 - The epidemiology and control of heuchera rust

Start Date: 
Completion Date: 
Project Leader: 
Dr Erika Wedgwood, ADAS Boxworth
HNS 191

Industry representative: Neil Alcock

HDC project cost: £39,867


The Problem:
Heuchera rust, caused by Puccinia heucherae, was first identified within the UK in 2004. Since then, the incidence of the disease on nurseries has increased significantly on a range of species and varieties and it has been proving extremely difficult to control using a combination of fungicides and cultural control methods.
A range of species (H. americana, micrantha, sanguinea and villosa) are susceptible, as are individual varieties, including 'Marmalade', 'Lime Marmalade', 'Peach Flambe', 'Obsidian', 'Midnignt Rose', 'Plum Royale', 'Plum Pudding', 'Southern Comfort', 'Chocolate Ruffles', 'Melting Fire', 'Palace Purple', 'Lime Rickey', 'Sugar Plum', 'Beauty Colour', 'Ginger Ale', 'Mocha', Key Lime Pie', 'Silver Scrolls'). In addition, it appears that micropropagated hybrids can be particularly problematic for growers. Heuchera rust is mainly seen on older stock. although symptoms can be seen on younger plants of more susceptible varieties.
A number of research and knowledge transfer priorities have been identified and the HDC intends to fund a two year research programme to address these. The programme should focus on a balance of research and knowledge transfer activities. Work should build on current knowledge and not duplicate effort.
Aims and objectives:
To investigate and improve the understanding of heuchera rust and its epidemiology, specifically;
• Determine the origin of the infection by heuchera rust
• Elucidate the conditions when heuchera rust is most likely to occur
Objective 1: Survey and review for further information relevant to heuchera rust incidence
1.1 Survey heuchera growers to understand the pathway of disease introduction and conditions in which the disease is most likely to occur, including plant susceptibility, to guide investigations into the situations in which heuchera rust may appear.
1.2 Review global knowledge of heuchera rust and relevant epidemiological information from rusts on other hosts to guide investigations into conditions favourable to heuchera rust.
Objective 2: Determine if latent rust infection can be detected in heuchera from nurseries
2.1 Refine and apply a molecular test to confirm if the infection is due to Puccinia heucherae, or another rust species, and to detect the fungus on symptomless heuchera plants.
2.2 Apply the molecular test and collect and grow on heuchera plants to determine whether plants arriving at nurseries are infected.
Objective 3: Determine how differing irrigation periods may affect infection from rust pustules and if water demand affects symptom expression from latent infection
3.1 Study the effects of leaf wetness period and timing in the day on plant infection by rust.
3.2 Study the effect of different water regimes on expression of rust symptoms in heuchera.
Objective 4: Knowledge transfer
4.1 Prepare annual and final reports, an article for HDC News and updates to growers.
4.2 Present findings to growers and discuss outcomes at suitable HDC events.
Risks that may prevent or delay achievement of objectives:
The survey of growers will seek detailed information on their heuchera production which could involve them in additional work in checking, or be considered commercially sensitive and so we may not be able to obtain as much data as we would like. This could affect our ability to be able to compare growing practices between those with and without rust on particular varieties or propagator sources. All information on rust problems that could be linked to particular growers will, however, remain confidential between Beatrice Henricot and Erika Wedgwood and care taken in how the work is reported.
The practical work will rely on both latent and visible rust on plants being obtained in sufficient quantities in time for the start of experiments. Heuchera rust has not been as widespread in 2013 and this could also happen in 2014 and 2015. This obligate fungus cannot be held in agar culture and spore preservation, if possible, would not be ideal in epidemiology tests. Preliminary experiments will seek to obtain infection under optimum conditions before it will be possible to study the parameters in more detail.
The outcome of the proposed molecular work to determine if latent infection can be detected cannot be predicted and there is a risk that it will be found that detection is not possible by the use of conventional polymerase chain reaction (PCR). Work on chrysanthemum rust has, however, shown detection possible by this technique four days post-infection, 10 days before any visible symptoms.