Viral infection and nicotine conversion to nornicotine in the next generation
In tobacco, nicotine demethylation to nornicotine may occur during leaf maturation and yellowing. The gene involved in this transformation is present in any plant whereas it is activated only on some, called "converters".
The appearance of such converters in the descent of non converter plants of burley inbred lines is a frequent phenomenon, thought to be linked to epigenetic events that would affect the regulation of the nicotine demethylase gene.
In order to test the effect of viral infections on such events, the following experiment was performed at Bergerac (France). In 2006, the burley inbred line TN 90LC was grown. Three weeks after transplantation the following treatments were applied, each on 25 shoots:
- Not inoculated,
- Mock inoculated with water,
- CMV inoculated,
- PVY inoculated,
- CMV + PVYN inoculed.
Viral symptoms were recorded on inoculated plants and ELISA tests confirmed the virus presence. Seeds were harvested from 10 individual plants in each treatment.
In 2008, respectively 100, 100 and 200 shoots from the seeds of treatments 1, 2 and 5 plants were grown. Mature middle leaves were individually harvested, air-cured, and analysed for alkaloids. The frequencies of converters (nicotine to nornicotine conversion ratio > 10%) were found to be 14, 6, and 26%.
In 2010, respectively 50, 100 and 100 shoots from the seeds of treatments 2, 3 and 4 plants were grown and analysed, and the frequencies of converters in these descents were 10, 15 and 26%. This suggests that viral infection, in particular PVY, is associated with a higher frequency of converter plants in the descent. It fully justifies discarding virus infected plants as soon as possible during tobacco seed production.