Source: The Scottish Farmer [summ., edited]
Cereal diseases like common bunt (_Tilletia tritici_) have rarely been seen over the past decade as seed treatments have been highly effective. But there has been an increasing trend against seed treatments in both farm-saved and certified seed, to save costs and support soil biology.
Bunt is re-emerging as a serious threat to wheat. A 5-year seed disease resurgence trial has recorded exceptional levels of bunt in untreated farm-saved seed plots, unexpectedly already in year 2. Both wheat and barley seeds were used in treated and untreated trial plots. All plots received maintenance fungicide sprays during the growing season as required. Bunt infection in the untreated wheat plots averaged 15% of ears across the trial.
Experts are now cautioning against using untreated seed without first testing for any disease presence.
[Byline: Ken Fletcher]
[Common bunt, caused by the fungus _Ustilago tritici_ (previously _Tilletia tritici_), affects bread wheat (_Triticum aestivum_), durum wheat (_T. turgidum_), triticale (wheat/rye hybrids), rye (_Secale cereale_), and some grass species. Disease development is favoured by cool, humid conditions at time of planting. Infection occurs during seed germination via contaminated seeds or from spores in surrounding soil, but symptoms do not appear until heading. On infected seed heads, kernels are replaced by brown smut balls filled with malodorous spores ('stinking smut'); plants may be stunted and glumes distorted. At harvest, clouds of spores are released, but some bunt balls remain intact and mix with healthy grain. Economic losses are due to reduction of grain quality and yield.
Spores can be spread with plant material, especially seeds, and consequently farm saved seeds pose a high risk of spreading the fungus. The pathogen can also be transmitted by contaminated equipment; human activities; and over long distances by wind. Spores can survive on seeds and in the soil for decades. Disease management may include cultural and phytosanitary measures, fungicide seed treatments, and use of certified clean seed. Some resistant crop varieties are available, but many newer wheat varieties are susceptible since bunt has not been a priority for farmers in a long time.
Pathogens previously classed in the same genus cause karnal (_T. indica_) and dwarf bunts (_T. contraversa_) of the same hosts, as well as black smut of rice (_T. barclayana_).
Common bunt on wheat:
Information on common bunt of wheat:
and via https://www.agric.wa.gov.au/barley/smut-and-bunt-diseases-cereal-biology-identification-and-management?page=0%2C1
_U. tritici_ life cycle:
_U. tritici_ taxonomy & synonyms:
Other fungal taxonomy via: