Tilletia controversa

Dwarf bunt

General

Tilletia controversa is a plant pathogen. It is a fungus known to cause the smut disease TCK smut in soft white and hard red winter wheats, as well as dwarf bunt.

Life cycle and appearance of Dwarf bunt

Tilletia controversa survives as teliospores in the soil or on seed. The soil-borne teliospores are the main source of primary infection. The soil-borne teliospores may survive in soil without suitable host for as long as ten years. Seed-borne transmission does occur, but is less important from an epidemiological point of view.

The teliospores germinate in response to moisture and form basidiospores, also called primary sporidium. Two mating types are distinguished. The filiform basidiospores fuse in the middle with a basidiospore of the other mating type so that H-shaped structures are formed. These can germinate directly or form secondary sporidia. These sporidia infect the wheat seedlings even before emergence and the fungi grow inside the plants to the growing tip. The fungi grow between the plant cells and eventually grow inside the kernels. When that happens, the fungal mycelium turns into teliospores and the whole kernel becomes a bunt ball full of teliospores. These balls break during harvest allowing the teliospores to fall to the ground. Additionally, these teliospores contaminate healthy kernels, which in turn become a source of disease in the next season.

The optimum temperature for germination is 3-8 °C and it takes three to ten weeks for germination. The seedlings are infected after emergence; the two- to three-leaf stage plants are most susceptible. This disease occurs mostly at some elevation and after prolonged snow cover which ensures a period of low soil temperatures.

Damage symptoms

Tilletia controversa causes (bunted) heads that are slender and remain green longer than healthy heads. The glumes are opened either on some or on all spikelets, showing the bunt (smut spore) they contain, which is larger than a normal kernel. The bunt balls are grey-brown. They rupture at harvest and release black, powdery spores, that smell like fish, hence the common name stinking bunt.

Additionally, plants only reach a fraction of their normal height. Spikes are generally broader and the glumes opened wider, than in plants infected with Tilletia tritici and Tilletia laevis

How to prevent Dwarf bunt

  • Use resistant cultivars. However, the fungi may form new isolates that can break resistance
  • Use clean, disinfected seed
  • The use of soil fungicides can help reduce the soil-borne inoculum
  • Sowing winter crops early in the fall when temperatures are still above 15°C at the critical first 11 days reduces the risk of infection by Triticum tritici and Triticum laevis. Since Triticum controversa mostly attacks the 2-3 leaf stage, this is less effective for this fungus

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