Cracks, fissures and clefts: different appearances of external tuber disorders

February 07, 2022
Author: PotatoWorld editorial

Tuber cracks, fissures and clefts have different appearances following different causes. They are healed wounds but clearly visible as scars on the surface. These healed fissures are generally oriented in the length direction of the tubers and are more present at the rose end than at the bud end of the tuber. They are triggered by a sudden change in growing conditions.

When after a dry spell without rain or irrigation, the crop is suddenly irrigated or when it starts to rain again, the tuber takes up water. As a result, it swells, or at least attempts to do so and becomes more turgid. The resulting internal pressure is too much for the outer skin and it bursts. A heat wave has the same effect, as at high temperatures the tuber stops growing and resumes growth when the temperature drops again.

Growth cracks related to potato diseases

Some diseases are related to growth cracks such as potato virus Y (PVY), potato mop top virus (PMTV) and the fungus responsible for black scurf (Rhizoctonia solani). Cultural practices such as narrower spacing, well balanced irrigation, even distribution to the soil and moderate nitrogen fertilization contribute to the reduction of the phenomenon. Other external cracks are smaller than growth cracks such as the ‘thumbnail cracks’ caused by drying of the surface of very turgid tubers.

Image: Tubers show cracks following irregular growth because of diseases or irregular or nitrogen water availability and or temperatures. Thumbnail cracks are due to drying of turgid tubers. Moreover, viruses (PVY causing mosaics) and fungi (Rhizoctonia solani causing black scurf) lead to tuber cracking.

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