Shatter bruises

• Symptoms

Shatter bruises (fracture damage, external or split damage) are wounds characterised by sometimes deep and extensive breaks in the cell walls. Depending on the symptoms, they will be named as follows: cracks, open shatters or internal crushing (photos 1 and 2). Breaks are directly visible on the skin of the tuber immediately following strong impact. With starch potatoes, major crushing may cause the release of starch grains, inducing “starch pile” symptoms (photos 3 and 4).

The use of colouring agents (iron perchloride, pyrocatechol) facilitates visual detection if applied as soon as the injury occurs. The lesions, which also affect the tuber flesh and take several days to heal, provide an easy entry point for different rotting agents (Phoma spp., Fusarium spp., Pectobacterium spp., etc.).

• Risk factors

The susceptibility of the cultivar plays an important role in this type of wound. Under the same conditions of production and for the same force of impact, some cultivars burst completely while others only have a few shallow cracks. Apart from this cultivar aspect, a number of other factors can increase the tuber’s intrinsic susceptibility: high turgor pressure due to heavy rain and excessive irrigation, immaturity, premature lifting and low handling temperatures.

• Control measures

Globally, all the mechanical equipment used to reduce tuber damage should be implemented throughout harvesting and handling operations: height of fall less than 30 cm, belt speed under 40 m/min, fall impact dampener, high-performance sheaths and foam protection, etc. During harvesting, the settings must be very accurately adjusted: chain rotation speed consistent with the engine speed (ideally, a ratio of 0.8 to 1.2), minimum shaking, minimum aggression by devices used for the elimination of haulms and clods. Preferably, harvesting must be done when the tubers have had sufficient maturation time in the soil to have a well suberised skin. At the same time, it is necessary to avoid too dry, too humid or too cold conditions. For all handling operations, the temperature of the tubers should never be less than 10°C.