Melanism and brown necrosis (also known as False black chaff)

1. Symptoms: Melanism occurs as brownish black to dark purple spots, streaks, or blotches on the leaf sheaths, stems (picture below at left), and/or glumes and results from a high production of melanoid pigments in some genotypes. The dark brown pigmentation usually develops on the glumes (picture at right, below) and peduncles. Melanism and brown necrosis may be confused with black chaff or stagonospora blotch.
2. Development: The symptoms develop under certain environmental conditions, in particular with cloudy, humid weather and a high intensity of ultraviolet light (high elevations). Melanism appears to be linked with the stem rust resistance genes from "Hope" and H44.
3. Hosts/Distribution: Melanism occurs wherever wheat is grown, but is more pronounced in high radiation, high humidity environments.
4. Importance: Generally not a serious problem; some crosses exhibit severe necrosis and yield is affected.