Effect of XXXX seeds contamination rate by the @entity67471 on epidemics development.

@entity778 @entity67471 @entity281 @entity325 @entity11314
@entity67471 ( @entity67471 ) diseased seeds provide at seedling, @entity778 plants which are the only source of primary inoculum. @entity325 are bequeathed by aphids. The objective of this research is to study the development of the secondary @entity281 in field. Therefore, eight @entity11314 varieties with different seed contamination rate (0, 0.05, 0.25, 0.5, 1, 5%) were used over consecutive four years. The infected plants were recorded every week from the tenth day after sowing and over seven weeks. In the same way, aphids' population were evaluated in plots 30 days after sowing. There was no difference for the incidence rate between the average of plots sown with virus free-seeds and those sown with infected seeds with a rate of 0, 5%. In any case, the disease progressed lowly leading to incidences less than 50% at the post-flowering period in spite of a relatively high initial contamination rate of seed. For this group of varieties, the low progression of the disease indicated a high level of resistance to the @entity281 . The high levels of @entity281 especially observed with the varieties with high level of virus transmission to seed, translated the need to reduce aphids' population density notably by the use of insecticides during @entity11314 growing cycle. The high number of aphids and inoculum availability in the neighbouring plots were undoubtedly at the source of this result. This situation laid out the problematic of the use of seeds then little or not contaminated by the virus.
