Suellen Barbara Ferreira Galvino-Costa

Treatments with pyraclostrobin, a fungicide from the strobilurin chemical group, have induced physiological effects in several plants, which may influence their productivity. In this study, two experiments were carried out to study the effect of a commercial product containing pyraclostrobin + metiram on productivity and virus dissemination in potato cultivars. The first experiment was carried out in Maria da Fé-MG, applying different combinations of the product via furrow at planting and via foliar application, in post-emergence, using the cultivar Cupido and two fertilizer levels: 2,500 kg/ha and 3,500 kg/ha of NPK in the formulation 4:14:8. In the second experiment, eight French potato cultivars were tested in São Gonçalo do Sapucaí-MG, with applications of the fungicide via furrow and via foliar application. An interaction between the fertilizers and cultivars with the types of fungicide treatments used was observed. There was a significant increase of 13.6% in the production of the treated potato cv. Cupido, when the fungicide was applied in the furrow and the NPK level was 2,500 kg/ha. The production of all eight cultivars tested was higher in the treated plots, and the greatest productivity gain was 28% in cv. Eole. In both experiments, pyraclostrobin did not affect the spread of the virus in the field. This study showed that pyraclostrobin has the potential to increase potato productivity and reduce fertilizer use. However, the best treatment and the best fertilizer level should be determined for each cultivar, since the cultivars used responded differently to the same treatments.

Potato virus Y (PVY) is recognized as one of the most common and destructive pathogens seriously affecting potato producing areas worldwide. More recently PVY^NTN and PVY^N:O/N-Wi, have emerged as the main strains present in the PVY infected plants detected in Brazilian potato fields. In this study, samples of potato collected in south part of Minas Gerais - Brazil were first tested by DAS-ELISA and then by RT-PCR multiplex in order to discriminate the PVY strains. Afterward, part of them was tested by RT-qPCR to confirm and quantify the viruses in infected tissues. The sensitivity of the techniques for detecting PVY isolates present in the sampled locations was investigated, as well as the occurrence of mixed infections, aiming to understand the general epidemiological picture of this pathogen in potato producing fields. In the multiplex RT-PCR test, the samples with O and N serotypes were identified as infected with PVY^NTN and PVY^N:O/N-Wi strains. When tested by RT-PCR for amplification of PVY^E, 41 samples (67,2%) were positive, having a characteristic electrophoretic profile for this recombinant strain, and 9 isolates were also observed with atypical patterns for recombinant PVYE. The best technique to detect mixed infection was RT-qPCR, with the concentration of PVYNTN being much higher than that of PVYN:O/N-Wi. These results show the importance of using the most suitable method for the diagnosis and surveying of PVY strains in crop fields and reveal, for the first time, the dissemination of PVYE recombinants to several Brazilian potato fields.