Diffusione di ‘Candidatus phytoplasma asteris’ in colza

Oilseed rape (Brassica napus L. var. oleifera) is cultivated in about 25,000 Ha in Italy (ISTAT, 2009). The seeds are mainly employed for oil for the biodiesel production as well as for flour for animal feedings. During 2009 in Legnaro (PD) and 2010 in the same area as well as in Padova, Verona and Zevio (VR) oilseed rape production areas plants showing phytoplasma-like symptoms were observed. Witches’ broom, leaf malformation and with abnormal reddening, flowers with malformation and phyllody; in affected inflorescences only a small proportion of flowers set seeds that were shrivelling and not germinating. In May of the two years symptomatic samples were collected for nucleic acid extraction from shoots, midribs and petioles. Phytoplasma detection and identification were obtained with direct PCR using phytoplasma universal primers P1/P7, amplifying 16S rRNA and spacer region, followed by RFLP analyses with TruI and HhaI as restriction enzymes. All samples were positive and showed identical RFLP profiles with the two enzymes that were indistinguishable from the one of European aster yellows (16SrI-B) reference strain belonging to ‘Candidatus Phytoplasma asteris’. The same phytoplasma was reported in oilseed rape from Bertaccini et al. (1998) in the Czech Republic and from Maliogka et al. (2009) in Greece. In Italy after its first report (Rampin et al., 2010) it is slowly spreading. During the two years survey 51 cultivars of diverse genetic types (hybrids CHH, CHH semi-dwarf, CHL and free pollinates lines) and having diverse qualitative characteristics (LEAR and HEAR, with low and high content of erucic acid respectively) were tested. Among those 31 showed the above described symptoms with incidences ranging from 0.03% to 1.89%. The phytoplasma diffusion seems not to be influenced by fertilization, while the number of seeds per square centimetre appears to influence its spreading. In all examined fields a gradient of disease from filed borders toward the centre was observed leading to the hypothesis of important activity of insect vectors. Aster yellows phytoplasma is naturally transmitted by different leafhoppers such as Euscelidius variegatus (Kirschbaum), Euscelis incisus (Kirschbaum), Macrosteles quadripunctulatus (Kirschbaum), Macrosteles quadrilineatus (Forbes) and Macrosteles laevis (Ribaut) all quite commonly present in the Padano-Veneto agricultural areas.