Occurrence of potato mop-top virus in Northwest of Pakistan

Abstract

The Northwest of Pakistan is the leading seed potato producing area of the country. The long presence of powdery scab in potato in the region led us to investigate the occurrence of potato mop-top virus (PMTV) in potato cultivars commercially grown in the region. We surveyed the hilly region, particularly Malakand and Hazara divisions, over 3 years i.e. 2010–2012. We found that PMTV is prevalent in Northwest of Pakistan and were detected in almost all potato cultivars commercially grown in the region. The highest mean percent incidence (19.0 %) of the virus was reported from a field in zone F (Abbottabad) followed by 15.6 % in zone G (Manshera) in Hazara division. In Malakand Division (Zone A–E) the incidence was lower (5–12 %) than Hazara Division. We observed an increase in virus incidence in 2012 as compared to 2010 and 2011 in all major potato growing zones. The identity of the virus was confirmed through bait bioassay, enzyme-linked immunosorbent assay (ELISA) and reverse transcription-polymerase chain reaction (RT-PCR) in leaves and roots of bait plants, tubers of commercially grown cultivars and also in zoospores of its vector, Spongospora subterranea. Our results indicate that the virus was prevalent in at least 25 (out of 26) sampling locations. We found that internal browning symptoms were positively correlated with the presence of the virus in the tubers when tested through ELISA. The results were further confirmed through RT-PCR in potato tubers with brown arc.