Results of artificial inoculations of 8 combinations of rootstock/pear cultivar by 'Candidatus phytoplasma pyri'.

Because the pear varieties Conference, Comice and William, grafted in open field on different rootstock resulted susceptible to 'Candidatus phytoplasma pyri', transmitted by Cacopsilla piry, and, in the same orchard, sixty-eight apricot varieties resulted differently susceptible to 'Candidatus phytoplasma prunorum', we planned a work program with the aim to discover a source of immunity among six new combination of pear varieties/rootstock and seven new combination apricot varieties/rootstock, exposed to the contact with the associated phytoplasma micro-organisms, by patch grafting of infected tissues on their phloem. We used also one pear combination and one apricot combination already resulted, in open field, both susceptible to the associated phytoplasma, transmitted by the specific vectors. These experiments were carried out on health young plants, cultivated in pots, under insect proof greenhouses, since 2002 to 2008. The molecular analyses using PCR/RFLP technology to verify pathogen presence were carried out every season from 2003 to 2008. The new pear combination resulted susceptible to ‘Ca. phytoplasma piry’ is William on Pirus betulaefolie but the evidence that either the pear combination or the apricot combination, resulted in the past susceptible, were resulted, in these experiments, negative to molecular test does not permit us to declare immune all the other new combinations tested. So we can conclude or that this kind of grafting cannot be trusted with transmitting these two pathogen to young plants, cultivated in pots, or that it is necessary to find new molecular methods to detect few genomic copies of these two pathogens.