Regulated Non-Quarantine Projects

Two EU funded projects for the benefit of the whole EPPO region

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Justification for qualification based on EPPO PM 4 Standards
Justification for disqualification
Additional or non-conclusive information
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NAME OF THE ORGANISM: Tilletia controversa (TILLCO)


GENERAL INFORMATION ON THE PEST

Name as submitted in the project specification (if different):
 

Pest category:
 
Fungi


1- Identity of the pest/Level of taxonomic listing:

Is the organism clearly a single taxonomic entity and can it be adequately distinguished from other entities of the same rank?
 
Yes

Is the pest defined at the species level or lower?:
 
Yes

Can listing of the pest at a taxonomic level higher than species be supported by scientific reasons or can species be identified within the taxonomic rank which are the (main) pests of concern?
 
  • Not relevant: Cereals (including rice) sector
If necessary, please list the species:
 
-

Is it justified that the pest is listed at a taxonomic rank below species level?
 
Not relevant

Conclusion:
 
  • Candidate: Cereals (including rice) sector
Justification (if necessary):
 
Remark: Tilletia controversa is closely related to T. caries (syn. T. tritici) and T. laevis. The species can readily hybridize together (Bockus et al., 2010; CABI, 2020). In the responses to the questionnaire, DE indicated that the different species of Tilletia are difficult to distinguish from each other microscopically. A reliable differentiation using PCR does not currently exist.

2 – Status in the EU:
 
Is this pest already a quarantine pest for the whole EU?
 
No

Presence in the EU:
 
Yes

List of countries (EPPO Global Database):
 
Austria (1993); Bulgaria (1993); Croatia (1996); Czech Republic (2011); Germany (2020); Greece (1992); Hungary (2012); Italy (1992); Latvia (2007); Luxembourg (1988); Poland (2019); Romania (1992); Slovakia (1998); Slovenia (1995); Sweden (2021)

Conclusion:
 
Candidate

Justification (if necessary):
 
Data of the presence of this pest on the EU territory are available in EPPO Global Database (https://gd.eppo.int/). It is considered that, very probably, T. controversa has already reached the limits of its potential natural distribution in the EPPO region (CABI, 2021).
Remarks: In Germany, the pest is not reported every years, and was not reported during years 1984-1996 (EPPO Reporting Service 1996/29). It was reported having a restricted distribution (EPPO Reporting Service 1998/203). Rudloff et al. (2020) reports that the pest is mainly in the southern part of Germany, in organic production, and at low incidence in conventional fields in Northern Germany in 2016-2017. Use of seed and perhaps plant treatments with fungicides (triazole on the soil surface) may have been responsible for such different situations reported. The disease is not observed in France under the present surveillance effort. Same situation may occur in Denmark, Spain, Portugal and the United Kingdom according to EPPO Global Database (Delos, pers. comm., 2024).

HOST PLANT N°1: Triticum aestivum (TRZAX) for the Cereals (including rice) sector.


Origin of the listing:
 
New proposal

Plants for planting:
 
Seeds


3 - Is the pest already listed in a PM4 standard on the concerned host plant?
 
No
 
Conclusion:
 
Evaluation continues

4 - Are the listed plants for planting the main* pathway for the "pest/host/intended use" combination? (*: significant compared to others):
 
Yes
 
Conclusion:
 
Candidate

 
Justification:
 
Natural infection of hosts other than wheat is less common (Bockus et al., 2010). In addition to Triticum aestivum (wheat, especially winter wheat), xTriticosecale and Triticum turgidum spp. durum are also main hosts of Tilletia controversa (Vánky, 2012). Consequently, experts considered that (at least) these additional pest/host combinations should be assessed for the RNQP status.

T. controversa also infects Secale cereal (winter-sown rye), Hordeum vulgare (winter-sown barley), and various wild and cultivated grasses after artificial inoculation. These last hosts may not be relevant for RNQP regulation, but can be regulated at export by third countries for quarantine aspects.
Movement of wheat seed is a pathway since spores adhering the seed can contaminate uninfested soil, but the disease is only induced with this pathway when heavily infested seeds are planted. Ustilospores are also spread by wind on hundreds of kilometers and can contaminate soil but seems to play a relatively limited role in epidemics thanks to crop rotation (except for situations with organic wheat when the previous wheat crops were contaminated). The fungus can survive for up to 10 years in soil, germinating under a temperature optimum of 0-8°C (lower than for the common bunt), typically after preconditioning exposure to light, which conditions are found under persistent snow cover during 3-10 weeks. Temperature over 15°C inhibits spore germination (Bockus et al., 2010; CABI, 2021). However, in the last few years T. controversa and hybrids of T. caries x T. controversa were reported in regions, which would normally be too warm and mild for the pathogen. As winters aren‘t so cold anymore the pathogen finds optimum temperatures over longer periods without snow cover and is reported to grow in new regions (Thüringer, pers. comm, 2024). Contrary to common bunt, infection of winter wheat by T. controversa does not occur during seed germination to seedling emergence, but only after the seedling is well established. Therefore, seed is considered as a significative pathway compared to other, only under high inoculum density. Harvesters and other machinery passing from a contaminated production site to a pest-free one, as well as seed handling equipment, are also source of contamination (Bockus et al., 2010; CABI, 2021).

Experts considered that seed should be an important pathway for a grower not previously contaminated by the disease. In Austria, infections are sometimes reported in completely new regions and infections assumed to have been with seeds (Thüringer, pers. comm., 2024).

5 - Economic impact:

Are there documented reports of any economic impact on the host?
 
Yes

Justification:
 
Dwarf bunt is a serious disease, particularly of winter wheat at relatively high altitudes, and more recently in new regions which would normally be too warm and mild for the pathogen (see Pathway). It is very difficult to control because of the resistant resting spores which remain viable in the soil for a number of years. In the 1970s, the disease was reported to be of great economic importance in the EPPO region in Austria, Poland and the former USSR and of less economic importance in the other countries in which it is established (CABI, 2021). In Germany, losses of up to 30% have been reported (Murray & Wright, 2007). Dwarf bunt has the same effect on wheat quality as common bunt. If visually detected, the wheat would be unacceptable for human consumption and thus be downgraded to feed quality. The difference in value depends on the related market value of the grades, but feed wheat usually trades at 30–50% of the value of human consumption grades (Murray & Wright, 2007). Present yield losses in most countries where dwarf bunt occurs are minimal due to the effectiveness of current controls (modern seed fungicides). Recent reports of impact mostly relate to the production for organic farming. Similarly, organic farming had established specific thresholds few years ago for common bunt to manage the disease on seed.
Pest presence may cause additional impact for export of wheat and barley because T. controversa is a quarantine pest for many third countries.
Remark: Tilletia controversa may survive longer in the soil than T. laevis or T. controversa, and is considered more difficult to control with rotation.

What is the likely economic impact of the pest irrespective of its infestation source in the absence of phytosanitary measures? (= official measures)
 
Major

Is the economic impact due to the presence of the pest on the named host plant for planting, acceptable to the propagation and end user sectors concerned?
 
No

Is there unacceptable economic impact caused to other hosts (or the same host with a different intended use) produced at the same place of production due to the transfer of the pest from the named host plant for planting?
 

Conclusion:
 
Candidate

Justification:
 
It should be noted that economic impact depends on regional environmental conditions (favourable or unfavourable), race and available plant varieties (resistance).

6 - Are there feasible and effective measures available to prevent the presence of the pest on the plants for planting at an incidence above a certain threshold (including zero) to avoid an unacceptable economic impact as regards the relevant host plants?
 
Yes
 
Conclusion:
 
Candidate

Justification:
 
Dwarf bunt is primarily controlled by using resistant cultivars to particular races. At least 15 major resistance (Bt) genes have been identified in wheat and these genes influence host resistance to both dwarf bunt and common bunt (Bockus et al., 2010).
Because T. controversa infests plants after emergence, most fungicide seed treatments used for the control of common bunt are not effective against dwarf bunt. Active substances such as difenoconazole, systemic triazoles, SDHI or QOI fungicides, when applied in the field on susceptible wheat varieties, are effective against T. controversa and several other smut pathogens (Bockus et al., 2010; Delos, pers. comm., 2024). Contact fungicides such as Mancozeb are no longer authorized in the EU and the limited number of products available for organic farming is causing difficulties for pest management in organic farming.
Measures should consist in controlling that the pest presence is below a certain threshold for Tilletia species, without differentiating the species involved.

7- Is the quality of the data sufficient to recommend the pest to be listed as a RNQP?
 
Yes
 
Conclusion:
 
Candidate

Justification:
 

CONCLUSION ON THE STATUS:
 
Recommended for listing as an RNQP, based on data.


8 - Tolerance level:

Is there a need to change the Tolerance level:
 
Yes (new regulation proposal)

Proposed Tolerance levels:
 
A tolerance (not higher than an average of 5 to 10 spores per kernel in a sample, for T. caries, T. controversa and T. laevis together) with an alternative risk management measure (see risk management measures).

Justification (if necessary):
 
It is impossible to recognize different bunt species only based on field symptoms. Tilletia species may hybridize. Consequently, the threshold should be defined for the Tilletia ‘complex’. It should be based on an average of spores per seed in a sample.

No consensus was reached on the exact threshold to be used. The provided range is based on the experimental data available:
- A 3-year project evaluating the dynamic of T. caries infection when seeds are sown with a certain infection level, at different locations and for different varieties; and then harvested, saved and used again for two more times was performed (AGES, 2016; 2017). It shows that the infection level under 10 spores/seed resulted in low infection levels at least for two years, also in regions favorable for T. caries infection. It is consequently not recommended to use seeds with higher levels e.g. 20 spores/seed since in regions with favorable conditions, already in the second year, this is reported to cause high infection levels.
- An European Project (TESTA, 2013-2015) evaluated the transmission of viable T. caries to plantlets after artificial contamination of seeds sown under greenhouse and field conditions (https://www.eppo.int/media/uploaded_images/MEETINGS/Meetings_2015/testa_angers/07_Orgeur.pdf). This study showed that infection levels below 5 spores/seed resulted in low percentage of positive plantlets.
- Field data and theoretical spore load calculations confirmed that there is a risk potential for low-level infection. Independent of site and year, loads of 5 to 20 spores/seed of T. caries were sufficient to produce a distinct infection. A threshold of 20 spores/seed is too high for some susceptible cultivars (Waldow & Jahn, 2007).
Remark: based on experience, under German conditions, when using resistant cultivars, an average of 20 (viable) spores per seed is considered to be a threshold enough to prevent damage under conventional and organic farming. However Experts considered that this was not applicable in all situations in the EU.

Such thresholds are only necessary for untreated seeds. Lots which are planned to be treated or are already treated would not need to be tested in the laboratory.

National situation and regulation for Tilletia spp. is highly dependant on the importance of organic wheat seed production at national level.

9 - Risk management measures:

Is there a need to change the Risk management measure:
 
Yes

Proposed Risk management measure:
 
All categories (Pre-basic, Basic and Certified material):
(a) On a representative sample of seeds, infection with Tilletia caries, T. controversa and T. laevis should not exceed on average 5 – 10 (viable) spores per seed (Remarks: no consensus was reached on the exact threshold to be used. Viability testing is optional. When exceeding the threshold, viability test can be used to show that the threshold is respected for viable spores); or
(b) Seed treatment known to be effective against Tilletia controversa (Remark: option b should not be authorized when infection is known to exceed in average 150 (viable) spores per seed before the treatment. This should be systematically checked when infection with Tilletia spp. is reported during field inspection);

Field inspection and inspection of plots, pre and post control, may be used as an additional risk management measure to avoid any build-up of infection levels during the chain of propagation. Seed brushing may be used to achieve option (a). Stricter tolerance may be defined nationally.

Justification (if necessary):
 
Only untreated seeds should be tested in the laboratory and the threshold should only be valid for untreated seeds.

A maximum of 5-10 spores per seed should be used for all categories to avoid any build-up of infection (see thresholds). No consensus was reached on the exact threshold to be used.

Field inspection should not be considered as a standalone measure: In seed certification in AT, field inspection is mandatory. Although Tilletia isn‘t found very often in the field, lots infected with Tilletia sp. are regularly found. Additionally, seeds can also get contaminated after harvest with e.g. harvesting machines, contaminated trailers etc. Infection of other fields in the immediate vicinity may also be a source of contamination. Infection inside a non-broken seed may not be visible. Therefore laboratory testing should be performed for untreated seeds.

Experts discussed the available treatments for organic production. Contrary to T. caries and T. laevis, there are no fungicide organic seed treatments with demonstrated efficacy against T. controversa. Experts considered that seed brushing should only be used to achieve option (a). Brushing may be about 70–80% effective on seed-borne spores.
Consequently, if there is an infection higher than 5-10 (viable) spores/seed it is not possible to sell the lot as organic seed anymore. The only option is to treat it with a conventional seed treatment, then it can be sold as conventional seed.

Experts indicated that efficacy of seed treatments with triazoles or fludioxonil is close to 100% on seed-borne spores and at least 80% on soil-borne spores for triazoles.

For option (a), viability of the spores may not need to be systematically tested. However it can be an option for organic seeds, if the threshold was slightly exceeded.

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