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     Viruses

PMTV (Potato Mop Top virus)

TRV (Tobacco Rattle Virus)

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

PVY^NTN  (Potato Tuber Necrotic Ringspot Disease = PTNRD)

PVY^NTN (PTNRD)

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

Fungus

Violet root rot (Rizoctonia crocorum)

Visual diagnosis

Tubers are often covered with reddish-purple mycelial network. Under the mycelial mats, tubers may have dark gray spots covered with purplish black sclerotia

Cause

Rizoctoniacrocorum

Oomycetes

Pink rot (Phytophthora erythroseptica)

Pink rot (Phytophthora erythroseptica)

Visual diagnosis

Dark brown or black irregular on the tuber surface

Symptoms may show specifically around lenticels

External symptoms linked to lesions internally

Infected tubers may leak liquid from lenticels and feel spongy

Similar symptoms may be caused by Pythium spp. and Phytophthora infestans

Confirmatory diagnosis

Isolation onto agar from the leading edge of the internal lesion

Microscopoc observation of the spores

In the case of pink rot, the internal tissue turns pink within 30 min after exposure to air

Leak rot (Pythium spp.)

Late blight (Phytophthora infestans)

Golding bloch-like symptoms

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Visual diagnosis

Brown discoloration, golding bloch-like symptom; also occuring on red skin varieties

Causes

So far unidentified causes;  putative physiological disorders and/or uncomplete pigmentation