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Potato tuber blemishes: understanding & diagnosis

Other pitted or raised symptoms

Enlarged Lenticecels

Other pitted or raised
Other pitted or raised

Visual diagnosis

When the tubers spend a long time in wet soil,  initially, whitish outgrowths of lenticels are formed.

When soil becomes less moist, the tubers dry  and suberize leaving enlarged brown lenticels, which may be locally infected by various pathogens and become blackened

Cause

Heavy rainfall or exessive irrigation, especially in a badly drained soil

Potato cyst nematodes (PCN)

PCN

 

PCN

Visual diagnosis

Skin altered by very thin bite sites (pitting) of nematodes, only occurring under heavy soil infestation

Cause

Globodera spp.

Viruses

PMTV (Potato Mop Top virus)

Spraing

TRV (Tobacco Rattle Virus)

TRV
Visual diagnosis

Brown irregular lines and blotches

External symptoms linked to brown arcs and necrotic areas internally

Spraing due to PMTV or TRV are generally not typical enough to allow a precise diagnosis

Confirmatory diagnosis

Confirmatory diagnosis relies on serogical or DNA diagnostic tests

PVYNTN  (Potato Tuber Necrotic Ringspot Disease = PTNRD)

PVYntn

PVYNTN (PTNRD)

PVY ntn
Visual diagnosis

Brown blisters in the form of arcs, rings or lines

The necotic tissues become later depressed and may even crack

The symptoms remain limited to the periderm

Confirmatory diagnosis

Confirmatory diagnosis relies on serogical or DNA diagnostic tests

Potato tuber moth

More other pitted and raised

Visual diagnosis

Tunnels produced by potato tuber moth larvae at feeding in the flesh ; frass may be present, degrading the quality of presentation. Larvae can be found hiding in tunnels

Cause

Tuber moth larvae

Flea beetle larvae

More other pitted and raised

Visual diagnosis

Characteristic superficial trails resulting from suberized skin after larval feed of Epitrix species ; larvae are never resting in the trails, there is no presence of frass  

Cause

Epitrix spp.

Chemical damage

Other pitted or raised

Visual diagnosis

Prominent brown areas on the tuber surface

Cause

Application of CIPC on wet and immature tubers

Other holes 

Other pitted or raised

   

Dry core hole

Visual diagnosis

Holes surrounded by corky tissue

Cause

So far unidentified causes;  putative cause is R. solani