Occurrence of Potato Tuber Necrotic Ringspot Disease (PTNRD) in Italy.

Potato tuber necrotic ringspot disease, caused by a tuber necrotic isolate of potato virus YN named PVYNTN, was originally described in Hungary in 1980; later on, the disease spread throughout northern and eastern Europe (1). Recently, the virus was reported in Portugal (2) on fresh-market potatoes. During the summer of 1997, the disease appeared in the north of Italy, causing serious damage in processing and fresh-market potatoes. After harvesting, we observed in most of the potato cultivars tubers showing the typical superficial necrotic rings and areas. These viral lesions were predisposed to secondary infection by fungi and bacteria. Moreover, PVYNTN causes degradation of tuber starch into simple carbohydrates. This metabolic activity resulted in undesirable browning in chips. In different areas of northern Italy, samples were collected from 48 stocks of cv. Hermes, the most important processing cultivar in Italy, and from 12 stocks of other potato cultivars (Ernterstolz, Liseta, Monalisa, Primura, Kennebec). The original seed of the stocks came from five different European countries: Austria, Italy, Scotland, Switzerland, and The Netherlands. Samples were serologically tested by indirect enzyme-linked immunosorbent assay with specific monoclonal antibodies to tobacco venial necrosis strain group of PVY. The results showed that 37 out of 60 analyzed stocks were infected by an isolate belonging to PVYN group, 7 stocks were infected by a common isolate of PVY, and 16 were PVY free. To distinguish the tuber-necrosis isolate (PVYNTN) from the PVYN isolates, reverse transcription-polymerase chain reaction (RT-PCR) and immunocapture-RT-PCR were carried out with specific primers for PVYNTN (3). Both tuber and leaf sap were tested. RT-PCR was performed on tuber sap and immunocapture-RT-PCR on leaf sap. Leaf and tuber sap of healthy, PVY-infected, and PVYNTN-infected tobacco was used in each experiment. At least two tubers from each of 32 PVYN-infected stocks were included in the molecular assay. All samples showed an amplified product of the characteristic size for PVYNTN (835 bp), whereas neither the healthy control nor the PVY sample gave a product. All tested cultivars were infected and all countries from which tuber seed came revealed infected stocks. The high proportion of samples in which PVYNTN was detected suggests that the virus is now endemic to potato-growing regions of northern Italy. The weather in these regions during 1997 was mild and drought in winter-spring and very warm in late summer; these conditions were ideal for disease diffusion by vectors and for symptom development. This is the first report of the occurrence of PVYNTN in Italy. References: (1) C. Kerlan. Le Pomme de Terre Française 498:40, 1997. (2) M. C. Serra and H. L. Weidemann. Plant Dis. 81:694, 1997. (3) H. L. Weidemann and E. Maiss. Z. Pflanzenkrank. Pflanzenschutz 103:337, 1996.