Pyricularia oryzae Triticum lineage causing wheat blast: addition to the Alert List
Why: Wheat blast, caused by the Triticum lineage of Pyricularia oryzae, is a fungal disease of wheat (Triticum aestivum) that causes significant economic damage in South America. It has spread to Asia and Africa. There are currently no sufficiently effective control methods for P. oryzae Triticum lineage. Considering the importance of wheat in the EPPO region, and the potential impact of P. oryzae Triticum lineage, the EPPO Panel on Phytosanitary Measures recommended that it is added to the Alert List.
Note: P. oryzae Triticum lineage was previously classified as a unique species Pyricularia graminis-tritici, however it is no longer considered a distinct species but a lineage of P. oryzae with a host specialism for wheat, distinguishing it from other lineages of P. oryzae which have specialisms for other Poaceae species.
Where: P. oryzae Triticum lineage was originally observed in 1985 in Parana state in Brazil, before quickly spreading across the country. In the late 1990s and early 2000s it spread to neighbouring countries in South America. It has since been reported in Asia where it was found in Bangladesh in 2016, possibly introduced via seed imports from South America, and in Africa where it was found in Zambia in 2017. It was reported in the EPPO region in Serbia in 2023 based on morphological characteristics, but the formal identification of P. oryzae Triticum lineage has not yet been confirmed by molecular analyses.
Africa: Zambia
Asia: Bangladesh
South America: Argentina, Bolivia, Brazil (Brasília, Goiás, Mato Grosso do Sul, Minas Gerais, Rio Grande do Sul, São Paulo), Paraguay, Uruguay.
On which plants: The main host of P. oryzae Triticum lineage is bread wheat, Triticum aestivum. Although, it is reported on other Poaceae hosts including durum wheat (Triticum durum), oat (Avena strigosa), rye (Secale cereale), triticale (x Triticosecale) and barley (Hordeum vulgare) alongside several wild grasses which may be weeds (e.g. Cynodon spp., Digitaria spp., and Lolium spp.).
Damage: On wheat P. oryzae Triticum lineage infects all aboveground parts of the plant.
Leaf infection often occurs before symptoms are seen on the spikes. Infections on a leaf are characterized by diamond-shaped or elliptical necrotic lesions, with a reddish brown margin and white centre, on the upper side of the leaf and dark grey lesions on the underside of the leaf. The shape and size of these lesions varies depending on the growth stage of the plant, cultivar susceptibility and environmental conditions. In susceptible cultivars, if seedlings are infected this can lead to plant death.
However, the most damaging symptom in the field is head (spike) blast, which can be confused with Fusarium head blight. Typical head blast symptoms include partial or complete spike bleaching and shrivelled and deformed grains. Grey sporulating lesions can be seen on the neck (rachis). In severe cases, blackening and necrosis of the rachis is observed. If infection occurs during the flowering stage of wheat very little or no grain is produced. If infection occurs during the grain filling stage, small, shrivelled and discoloured grains are produced. Grain yield losses have been reported in the range of 10-100%. Yield loss is attributed to reduced spike weight, low grain filling and sterility issues.
Pictures are available in https://gd.eppo.int/taxon/PYRIOT/photos
Dissemination: P. oryzae Triticum lineage reproduces asexually in the field. Conidia (asexual spores) are released from lesions on the plant. Conidia are dispersed by wind and rain splashes onto neighbouring hosts. Dispersal is most efficient during periods of warm (18 – 30°C) and humid weather.
P. oryzae Triticum lineage can also be transmitted by seeds. The pathogen can survive in seeds for up 22 months. Seed transmission is the primary method of long-distance dispersal of the disease.
Pathways: seeds of host species.
Possible Risks: Wheat is an economically important crop that is widely grown in the EPPO region. P. oryzae Triticum lineage requires warm and humid conditions for dispersal. Within the EPPO region, climatic modelling suggests that it could establish and cause damage in the Mediterranean basin. A potential introduction of P. oryzae Triticum lineage poses a significant threat to wheat production as reported losses are very high. There are limited control strategies available, as chemical control measures and sources of genetic resistance are currently limited and further research is needed. Control measures centre on cultural practises to reduce inoculum pressure (e.g. adjusting sowing date to avoid flowering and grain filling during high temperatures and high humidity, crop rotation with non-grass crops, deep stubble ploughing, destruction of crop residues and alternate grass hosts), use of tolerant/resistant wheat varieties (some cultivars show moderate to high host resistance), while various chemical and biological products can reduce but not eliminate damage. Considering the potential damage to wheat, strict import controls and seed testing are needed to prevent accidental introductions.
Wheat blast could also emerge in the EPPO region after a host jump from the Lolium lineage to wheat, as the Lolium lineage is already widespread in the region.
EPPO RS 2025/127
Panel review date –
Sources
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