The effect of temperature on loose smut of wheat (Ustilago nuda)

In experiments made in controlled-temperature rooms on the wheat variety Kota, inoculated with two races of Ustilago nuda (Jens.) Rostr., maximum smut development occurred at 23 °C; at 20 ° and 15 °C the incidence and extent of smutting was reduced. An even greater reduction occurred when seedlings were grown at 6 °C for 2 months. No marked effect of temperature on mycelial development within the spike was observed until the ear emerged, when the mycelium in many of the ears of plants subjected to the lower temperatures failed to sporulate. The date of sowing in the field influenced disease development, presumably through the period of exposure to winter temperatures. Variety Little Club inoculated with race C₃ showed a similar but less marked response to cold-treatment.