Visual diagnosis

Cracks

• Tubers split while still growing
• Cracks associated with uneven growth  of the tuber frequently start at the bud or apical end of the tuber and can extend lengthwise. If cracking occurs in different directions their may be other causes
• When tubers are mature, the surface, within the crack, has a corky appearence

Deformations

The type of deformation depends on when abiotic factors occur :

• At the beginning of tuberisation, interrupted growth causes a constriction at the basal end of the tuber giving a pear-shape
• During tuberisation, the tuber may split into two parts, dumbbell-shaped tubers
• At the end of tuberisation, outgrowth develops at the tip of the rose end (sucker), or at several lateral eyes, tuber with multiple knobs

Potential causes

Tuber deformation and cracks are the results of physiological reactions of the tuber during its growing period

• One of the main causes of tuber cracks and deformations is an irregular water uptake during the growing period : dry periods alternating with rainfalls

• Another cause of growth cracking (usually unexpected) is the treatment of the folliage with an unappropriate pesticide causing phytotoxicity (herbicides)

•  Other abiotic factors such as over or poor nitrogen fertilisation, high temperatures... may also result in tuber cracking

• Some potato cultivars are more subject to such overall tuber deformation than others.

Specific reference:

Hiller etal (1985). Physiological disorders of potato tubers. In: Potato physiology. Ed.HL Paul. Academic Press, Orlando, Florida, USA. Pp. 389-455

Rhizoctonia cracking

Virus cracking