Potato diseases in the Andes
In the Andes, it is considered that the status of fungal and bacterial diseases has not changed much during the last 10 to 15 years but that the situation of viruses has been substantially modified. The following points can be noted:
Phytophthora infestans: outbreaks of mating type A2 of potato late blight have been observed in Bolivia. In the Andes, A2 mating type is reported only in Bolivia (in South America, it is also reported in non-Andean countries such as Brazil and Argentina). It is considered that the emergence of the A2 mating type is the result of seed movements from the Northern hemisphere.
Ralstonia solanacearum (EPPO A2 list): bacterial wilt was the most important bacterial disease spreading in the Andes during the last 10 years. Biovars 1, 2A and 2T occur throughout Peru; only biovars 1 and 2A were found in Bolivia.
Streptomyces scabies: a high incidence of common scab was observed in some localities in Bolivia (incidence of 30 to 40%, with up to 20% yield losses).
PVYNTN: isolates of Potato virus Y (Potyvirus) causing tuber necrosis have been found in some countries, including Peru. Studies suggest that these isolates have always been present in the Andes and were probably spread with other potato viruses when the crop was introduced into Europe during the XVI century.
Two new uncharacterized potato viruses: SB26/29 and SB41
SB26/29 can cause severe symptoms such as mosaic, foliage deformation, dwarfing and severe growth reduction. Yield reductions varying from 30% to 80% according to the potato cultivar have been observed. This virus is spreading in Peru, and has been shown to be transmitted by a psyllid vector (Russelliana solanicola, Homoptera: Psyllidae). Isometric viral particles have been observed, but so far the virus could not be purified.
SB41 can cause severe mosaic on potato. In experiments, it could be transmitted only by grafting and could also infect tomato (severe mosaic and deformation).
Potato yellowing virus (tentative Alfamovirus): it is commonly observed in the Andes, causing systemic yellowing of the foliage. It is transmitted in a semi-persistent manner by aphids and potato true seeds (on which it can cause a necrosis).
Pepino mosaic virus (Potexvirus, PepMV – EPPO Alert List): PepMV has been found in some potato germplasm accessions growing in the field. So far, PepMV had only been reported from pepino (Solanum muricatum) and tomato (Lycopersicon esculentum) along the coast in Peru. Due to difficulties in isolating PepMV, the potato isolates could not be characterized.
Papaya mosaic virus (Potexvirus, PapMV): this virus was also found in some potato germplasm accessions. This was not found surprising because PapMV occurs in Ullucus tuberosus which is a tuber crop widely grown in the Andes in the vicinity of potatoes.
Potato yellow vein virus (tentative Crinivirus, PYVV): PYVV has spread during the last 7 to 10 years from Colombia and Ecuador to Venezuela and Peru, respectively. It is transmitted by Trialeurodes vaporariorum and can persist in symptomless perennial weeds (mainly Polygonaceae).
Potato mop-top virus (Pomovirus): symptoms associated with this virus (crinkle mosaic and yellow aucuba patterns) have increased among the native Andean potato cultivars from Venezuela to Bolivia.
Finally, it is noted that both Potato yellow dwarf virus (Nucleorhabdovirus) and Potato aucuba mosaic virus (Potexvirus) have practically disappeared from the Andean potato crops.
Sources
Salazar LF (2006) Emerging and re-emerging potato diseases in the Andes. Potato Research 49(1), 43-47.