FUSARIUM OXYSPORUM F. SPP. AND XANTHOMONAS CAMPESTRIS PATHOVARS: TWO IMPORTANT PATHOGENS OF WILD ROCKET FOURTH RANGE PRODUCTIONS IN SOUTHERN ITALY

Wild rocket (Diplotaxis tenuifolia) is an important fourth range species; the most of its Italian production comes from Southern Italy. Fusarium oxysporum (Fo) and Xanthomonas campestris (Xc) are two dangerous pathogens that affect this plant species and often are the cause of great yield losses.
Fo is the causal agent of plant wilting while Xc causes the black rot and bacterial leaf spot disease. Either Fo and Xc are seed-borne pathogens and because of their aggressiveness many farmers check the seed health before sowing. In the last years, we frequently isolated them from infected plant specimens. Moreover we analysed 57 seed samples to check Fo and Xc presence. Fo detection in the seeds was carried out by isolation on semi-selective agar medium and the suspected colonies were tested for pathogenicity using the dipping root inoculation method. The 6% of the tested seed samples resulted contaminated by Fo. To detect Xanthomonas sp. in the seeds, a modified ISTA protocol (7-019) was used; pathogenicity tests were performed by spraying and by pin inoculation methods on one month old plants. The identification of Xanthomonas-like colonies was performed by molecular and in vivo tests. According to Vicente description (2006), the strains with vascular behavior were identified as X. c. pv. campestris and were detected in the 6% of the analysed seed samples. The identity of these strains were confirmed by the positive PCR amplification in the hrpF and hrcC gene regions. Non-pathogenic Xanthomonas strains were frequently isolated from seed samples, too. The characterization of these Xanthomonas strains is still in progress and it will be completed by further molecular tests. Xc and Fo were frequently detected on wild rocket: much more stringent phytosanitary controls should be applied to the seeds to reduce the widespread of both pathogens in the cultivations.