Degeneration of seed caused by virus
The main factors that determine the rate of degeneration are:
- number of infection sources
- the presence and activities of vectors ( aphids)
High degeneration
In a high degeneration area with plenty of virus infection sources (fields, plants) and a big population of active aphids, an initially clean seed stock (< 0.1% virus) after 1, 2 and 3 generations has 1%, 10% and 100% virus respectively.
Low degeneration
In a low degeneration rate area the percentage of virus after 1, 2, 3, 4 and 6 generations is about 0.5%, 1.2%, 9%, 20% and 100% respectively.
In the very low degeneration area the virus percentage is still less than 10% after 7 generations.
Degeneration caused by virus (graph)-------Degeneration caused by virus (table)
Low degeneration areas (periods) are most suitable for seed production and here farmers also can use their seed stocks for a large number of generations.
Reduction of the spread of aphid transmitted viruses
With regard to reducing aphid transmitted virus infections the following measures are taken: