As the fourth most prevalent food crop, potato is very important in the global economy, but it is affected by numerous pests, and by many bacterial, viral and fungal diseases. Among these diseases, potato virus Y (PVY), which is transmitted from plant to plant by aphids, causes significant yield losses, but as far as we know, the economic impact of PVY in Europe has not been quantified. Our economic study covers a period of 13 years between 2004 and 2017 and is based on an analysis of statistical, economic and agronomic data, obtained from various stakeholders in the potato sector in Switzerland and the European Union, as well as from field experiments. In Switzerland, the economic loss due to PVY for seed and ware production was estimated at about 2000 and 200 CHF/ha, respectively. For the European Union, the annual losses were estimated at 187 M EUR, respectively 96 and 91 M EUR for seed and ware. These losses were due mainly to the cost of chemical treatments applied in seed potato production and the yield drop in ware potato production. However, based on literature, these significant losses are lower than those caused by potato late blight (Phytophthora infestans), which is considered to be the most economically damaging potato disease in Europe.

This study investigated the drought protection effects of six fungal and bacterial inoculants and ten consortia thereof on vegetative growth, nutritional status, and tuberization of potato under controlled and field conditions. It was hypothesized that microbial consortia offer improved drought protection as compared with single strains, due to complementary or synergistic effects, with differential impacts also of N fertilization management. Under NO₃⁻ fertilization, a 70% reduction in water supply over six weeks reduced shoot and tuber biomass of non-inoculated plants by 30% and 50%, respectively, and induced phosphate (P) limitation compared to the well-watered control. The P nutritional status was significantly increased above the deficiency threshold by three single-strain inoculants and eight consortia. This was associated with the presence of the arbuscular mycorrhizal fungus (AMF) inoculant Rhizophagus irregularis MUCL41833 (five cases) and stimulation of root growth (five cases). Additionally, Bacillus amyloliquefaciens FZB42 and AMF + Pseudomonas brassicacearum 3Re2-7 significantly reduced irreversible drought-induced leaf damage after recovery to well-watered conditions. However, the microbial inoculants did not mitigate drought-induced reductions in tuber biomass, neither in greenhouse nor in field experiments. By contrast, NH₄⁺-dominated fertilization significantly increased tuber biomass under drought stress (534%), which was further increased by additional AMF inoculation (951%). This coincided with (i) improved enzymatic detoxification of drought-induced reactive oxygen species (ROS), (ii) improved osmotic adjustment in the shoot tissue (glycine betaine accumulation), (iii) increased shoot concentrations of ABA, jasmonic acid, and indole acetic acid, involved in drought stress signaling and tuberization, and (iv) reduced irreversible drought-induced leaf damage. Additional application of bacterial inoculants further improved ROS detoxification by increasing the production of antioxidants but stimulated biomass allocation towards shoot growth at the expense of tuber development. The results demonstrated that microbial consortia could increase the probability of drought protection effects influenced by the form of N supply. However, protective effects on vegetative growth do not necessarily translate into yield benefits, which can be achieved by adequate combination of inoculants and fertilizers.

Potato virus Y (PVY) is considered the most economically damaging virus for seed-potato production. PVY isolates are usually divided into three historical PVY strains, namely PVY^C, PVY^O and PVY^N. More recently, recombinant strains named PVY^NTN and PVY^N-Wi appeared in Europe and North America, rapidly spread into seed-potato production and gradually replaced historical strains. This progression can be explained by several factors, including the differential susceptibility of cultivars to PVY strains. This article presents the results of a Swiss survey of PVY strains conducted in 2012 in which the progressive increase of the prevalence of PVY^N-Wi was observed. The occurrence of PVY strains in the two main potato cultivars grown in Switzerland, cv. Agria and cv. Charlotte, is described through the 2012 survey and one additional PVY strain survey conducted in 2014. Both surveys were completed with a mechanical-inoculation assay. The inoculation assay showed that cv. Agria is more susceptible to PVY^N-Wi than to PVY^NTN, whereas cv. Charlotte is susceptible to both strains. The inoculation assay also showed that the expression of symptoms on cultivars is strain-dependent. These results stress the major role of the resistance profile of cultivars to explain the balance of the PVY strains in potato crops.

Potato virus Y (PVY) is responsible for major viral diseases in most potato seed areas. It is transmitted by aphids in a non-persistent manner, and it is spread in potato fields by the winged aphids flying from an infected source plant to a healthy one. Six different PVY strains groups affect potato crops: PVY^C, PVY^N, PVY^O, PVY^N:O, PVY^NTN, and PVY^N-Wi. Nowadays, PVY^NTN and PVY^N-Wi are the predominant strains in Europe and the USA. After the infection of the leaf and accumulation of the virus, the virus is translocated to the progeny tubers. It is known that PVY^N is better translocated than PVY^O, but little is known about the translocation of the other PVY strains. The translocation of PVY occurs faster in young plants than in old plants; this mature plant resistance is generally explained by a restriction of the cell-to-cell movement of the virus in the leaves. The mother tuber may play an important role in explaining mature plant resistance. PVY is able to pass from one stem to the other stems of the same plant through the vascular system of the mother tuber, but it is unknown whether this vascular link between stems is permanent during the whole life of the plant. Two greenhouse trials were set up to study the spread of PVY in the vascular system of the potato plant. The PVY-susceptible cultivar Charlotte was used for both trials. It was demonstrated that all stems growing from a PVY-infected tuber will become infected sooner or later, and that PVY^N-Wi translocates more efficiently to progeny tubers than PVY^NTN. It was also demonstrated that the progressive decay of the mother tuber in the soil reduces the possibility for virus particles to infect healthy stems through the vascular system of the mother tuber. This new element contributes to a better understanding of the mechanism of mature plant resistance.