Stem Rust - Pathology

Pathology

The stem rust fungus attacks the parts of the plant which are above ground. Spores that land on green wheat plants form a pustule that invades the outer layers of the stalk. Infected plants produce fewer tillers and set fewer seed, and in cases of severe infection the plant may die. Infection can reduce what is an apparently healthy crop about three weeks before harvest into a black tangle of broken stems and shriveled grains by harvest.

Stem rust of cereals causes yield losses in several ways:

• Fungus absorbs nutrients that would otherwise be used for grain development.
• Pustules break through epidermis, which disrupt the plant's control of transpiration and can lead to desiccation and infection by other fungi.
• Interference with plant vascular tissue leads to shriveled grains.
• The fungus weakens the stems, which can lead to lodging (falling over). In severe cases lodging can make mechanical harvesting impossible.