Tobacco Pvy Virus
Some of our contracted farmers woke up to their tobacco affected by Pvy Virus in some areas in Mount Darwin and Centenary Districts. This virus is the one that can affect the quality of the leaf. Below is an extract of a paper on the virus courtesy of the TRB;
Potato virus Y (PVY) incidence on tobacco in Zimbabwe – trends in the last decade
“Potato virus Y is among the economically important viral diseases of tobacco in Zimbabwe. Although first described in potato in 1931 by Smith, the first report on tobacco in then Rhodesia was in 1963 describing a new hazard in tobacco seedbeds caused by “necrotic Virus Y”. Two strains of the virus, one which produces mosaic-type symptoms and another that causes leaf and veinal necrosis, have been observed on tobacco. The mosaic strain reduces leaf quality, while the necrotic strain is very destructive leading to serious yield losses. The necrotic strain continues to be a problem in late-planted field tobacco in Zimbabwe. The Tobacco Research Board was one of the participants in the CORESTA collaborative experiment monitoring PVY incidence and characterising strains on CORESTA-prescribed and some local cultivars since 1996/7. The global CORESTA data presented by Verrier and Doroszewska in 2003 was based on data on number of plants infected by PVY and symptoms expressed (mosaic or necrotic) on resistant and susceptible cultivars. From this data the PVY incidence, the percent of va breaking strains within the necrotic strains and the estimated frequency of va breaking strains were calculated. The trials continued after 2003 and the trends from 2004 to 2013 for Zimbabwe are discussed in this paper. Results show that PVY incidence varied among seasons. As expected the resistant cultivars showed little or no expression of the necrotic symptoms. Of the local cultivars tested, TB4 (a flue-cured line) exhibited high resistance to the necrotic strain of the virus. Results also indicated that in some seasons there was an increase in the incidences of necrotic symptoms on some formerly resistant cultivars which could be attributed to PVY strains breaking the resistance. The estimated frequency of va breaking strains within the necrotic strains was also high in two of the peak seasons. As most local cultivars are susceptible to the necrotic strain of the virus, efforts are currently underway to utilise TB4 to breed for resistance to PVY.”