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Symptoms and Signs

Wheat plants

Infected wheat plants often, but not always, tend to be slightly shorter than healthy plants (Figure 1). After heading, the spikelets of infected plants tend to "flare-out" and take on a greasy, off-green color. This "flaring out" of the spikelet is due to the expansion in size of the bunt infected seed that has become filled with teliospores. In cultivars that normally produce long awns (bristle-like structures), infected heads may have shorter awns, or even no awns (Figure 2). In place of normal seeds, infected kernels develop into "bunt balls" (Figure 3). These are the remnants of what would normally be a seed, but in its place, the seed coat remains intact with the inside converted into a black mass of spores (Figure 4). The name "smut," which is derived from the Germanic word for "dirty," comes from this black spore stage. The name "bunt" comes from a dialectic contraction of the term "burnt ears" to "bunt ear" and finally to just "bunt."


Figure 1	Figure 2	Figure 3


Figure 4	Figure 5

Wheat kernels

The earliest evidence of infection occurs shortly after ovaries would normally be pollinated. Infected ovaries appear greasy with a dark green cast. When squeezed, such ovaries reveal a mass of black spores that smell like rotting fish. This odor is actually that of trimethylamine, which is produced by the smut fungus. As the heads and kernels mature, the bunt balls develop into a hardened mass that looks like miniature footballs. The spores inside the mature bunt balls are released when the heads go through the combine harvester to produce the cloud of dust (Figure 5). This dust also smells of rotting fish. Occasionally, both healthy seeds and bunt balls are found in the same head.

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