Viruses and certification of olive in Apulia (southern Italy).
Of the 8 mechanically transmissible viruses known to infect olive in Italy, 4 occur in Apulia. All these viruses, as well as Verticillium dahliae and Pseudomonas syringae pv. savastanoi, are included in the list of pathogens for entering a national voluntary certification scheme which was formally established in 1993 by a decree of the Italian Ministry of Agriculture and Forestry. Although the incidence of viral infections of olive in Apulia is barely appreciable (<1%), in view of the implementation of voluntary certification, surveys and testing for selecting candidate mother trees with a sanitary status compatible with the requirements of the scheme, were initiated in 1990. A total of 310 symptomless plants belonging to 27 different oil and table cultivars were individually checked and found free from mechanically transmissible viruses. However, when 12 of these plants of 8 different cultivars were analysed for the presence of dsRNA, 6 contained 1 or more dsRNA molecules. It is concluded that dsRNA technology may help in identifying virus-diseased olive trees, and that latent virus infection may be much more widespread than previously thought.