The role of some weeds as hosts of Capsicum viruses in the rift valley parts of Ethiopia.

Abstract

Hot pepper (Capsicum annuum. L.) is a traditionally and economically important spice crop in Ethiopia. Chronic infection with viruses is reported as major constraint, that often force farmers to ban its production. However, epidemiological studies on these viruses are lacking in the country. Knowledge of the weed flora as virus reservoir is essential to reduce the spread of plant viruses. The potential role of some frequently and abundantly occurring weed species as host plants for Capsicum viruses was therefore investigated. Surveys were conducted during the 2000/2001 cropping- and off-season. Samples of various weed species revealing virus symptoms were collected from different districts. Collection was done from inside and at the border of pepper cropped and fallow fields. It was also performed along road sides and irrigation channels. The identity of the collected isolates was established based on serology, electron microscopy and host range studies. Moreover, seeds were collected from natural populations of the most prevalent weeds, namely Datura stramonium and Nicandra physalodes. They were grown under glass house conditions and tested for their ability to host viruses. To verify their role further, healthy seedlings from these weeds were artificially inoculated with all viruses isolated from weeds and Capsicum leaf samples. Natural infection of different Potyviruses with an average incidence of 33% in the weed samples were the most dominant. In addition, the occurrence of Cucumber mosaic virus, Tomato mosaic virus and Potato virus X in these weeds was demonstrated. However, none of the isolated viruses was found to be seed borne in the tested weed species and pepper crop (var.Mrkofanna) under glass house conditions. Recently, there was an explosion in population size of some solanaceous weeds, particularly Datura and Nicandra species in the area. The presence of infected weeds throughout the year means, that they are an important reservoir and source for secondary spread. It is suggested therefore, that a rigorous weed control is an important step to reduce the incidence of viruses infecting Capsicum in the area.