ERADICATION OF SHARKA IN APULIA: STATE OF THE ART

Extensive surveys were therefore carried out each year in commercial plantings and nurseries, during which careful visual observations were made and samples were collected for laboratory examination by immunoenzymatic (DAS-ELISA) and immunoelectron microscopy (IEM) procedures. A total of 375 nurseries and commercial orchards of apricot, peach and plum were inspected, and over 30,000 trees were individually tested. Plum pox potyvirus (PPV) infections were detected in 13 plum and two apricot orchards, totalling a surface of about 35 Ha and 5 Ha, respectively. Six plum plantings that had an infection rate exceeding 30% were pulled out, immediately. In the remaining plantings (both plum and apricot) the infection rate was lower than 10% and the uprooting was limited to infected trees. Whereas in plum orchards no additional infections were detected in the years that followed the elimination of diseased trees, a few newly infected plants were discovered each year, from 1989 to 1994, in the two apricot stands. No PPV infections were ever detected in peach, or in nurseries, or in mother plants stands. The results of the studies carried out so far indicate that there was no detectable secondary spread of PPV in plum orchards, and that its spread in apricot was extremely limited, thus liable to be controlled. It seems then that the eradication programme is likely to be successful, because of the low inoculum potential, slow vius spread, and rapidity of intervention. However, the recent discovery in northern Apulia of natural PPV infections in sweet cherry, a species that was not taken into consideration in the programme, calls for a re-appraisal of the situation.

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