Incidence and Characterization of Potato virus Y in Seed Potatoes in Tunisia

Abstract

Surveys during five consecutive years in four main seed potatogrowing areas of Tunisia revealed large differences in Potato virus Y (PVY) incidence. Infection rates at harvest ranged from up to 19% in Cap Bon and in Jendouba, to 31% in Kairouan and 48% in Manouba. However, infection rates were very low across the country in 2003 (1-5%), except in Kairouan, and rather low in 2004 (4-10%). Secondary infections in plants growing from imported seed potatoes were assessed to be 1-6% depending on region and year. Serological analysis of a first set of 90 samples collected in 2004-2005 revealed dominance of the PVY N group (90% of the total number of PVY positives). A second set of 44 isolates from samples collected in 2006 was further analyzed with a combination of serotyping, indexing on tobacco, and RT-PCR tests targeting four genomic regions (5′Ntr/P1, HcPro/P3, CI/NIa, CP). Thirty-five of these 44 isolates were typical PVY NTN isolates, with three recombination junctions in HcPro/P3, CI/NIa, and CP regions, respectively, whereas no recombination junction was identified in the genome of five isolates belonging to the PVY N group. One additional recombinant PVY NTN isolate was recovered from a mixed infection with a PVY O isolate. Only three PVY O isolates were recovered from the samples analyzed.

Biological, serological and molecular typing of potato virus Y (PVY) isolates from Tunisia

“…Here, preliminary results indicating the high prevalence of PVY (up to 80%) are in close agreement with the situation reported in numerous worldwide potato growing areas (Gray et al, 2010), especially in Northern Africa (Boukhris-Bouhachem et al, 2010;Djilani-Khouadja et al, 2010). All positive samples were largely geographically distributed in Tunisia except for the central part of the country (Sidi Bouzid), which showed the lowest rate.…”

“…All positive samples were largely geographically distributed in Tunisia except for the central part of the country (Sidi Bouzid), which showed the lowest rate. This could be due to climate and seems to be in accordance with other works on seed potatoes in Tunisia (Boukhris-Bouhachem et al, 2010). Several factors may have contributed to the widespread distribution of PVY in Tunisia, which is one of the largest producers of ware potatoes in North Africa.…”

“…The main sources of seed potatoes imported by Tunisian producers are Holland and France (Khamassy N, personal communication), where a wide range of PVY types have been reported since the 1980s . Furthermore, the absence of local well-established systems for multiplication and distribution of virus-free seed potatoes of high quality, the presence of alternate PVY hosts (weeds or crops) and the large range of aphid species present in Tunisia and able to transmit this virus (Boukhris-Bouhachem et al, 2010) will also contribute to PVY distribution. Furthermore, our data clearly showed that the PVY isolates were mainly necrotic PVY N strains (~73.2%).…”

“…Viral diseases are the major cause of poor seed quality and low yield. Potato virus Y (PVY) is reported to be one of the most detrimental potato viruses responsible for the major yield losses worldwide (Gray et al, 2010) and in Tunisia (Boukhris-Bouhachem et al, 2010;Djilani-Khouadja et al, 2010). The type-species is of the genus Potyvirus in the family Potyviridae, and this virus is a single-strand, positive-sense genomic RNA of ~9.7 kb.…”

“…The destructive effects of this threatening disease are a particular problem in consumption and seed potato production, as it makes tubers of susceptible cultivars unmarketable as fresh potato and since infected seed lots submitted for certification are rejected (Beczner et al, 1984). This disease is now well-known in Tunisia (Boukhris-Bouhachem et al, 2010) and in most countries cultivating potatoes (Singh et al, 2008). Immunocapture RT-PCR was used in this study for specific detection of PVY NTN isolates on the basis of the nucleotide sequence polymorphism observed in the 5'NTR/P1 region (Glais et al, 2005).…”