Discussion
Although the phytoplasmas ‘Candidatus Phytoplasma mali´,
‘Ca. P. prunorum´ and ‘Ca. P. pyri´ belong to the same
16SrX group, their pathogenicity is quite different in their respective
host plants Malus domestica (apple), Prunus persica(peach) and Pyrus communis (pear). Apple trees can survive a
phytoplasma infection for decades, whereas phytoplasma-infected peach
and pear trees often die after a few years and sometimes even after a
few weeks (quick decline of pear) (Fiore et al., 2019; Marcone et
al., 2010; Marcone & Rao 2019; Seemüller et al., 1986, 2018). This
indicates a higher tolerance resulting in better survival rate for
phytoplasma-infected apple compared with pear and peach; however, the
underlying reason is not known yet. To address this open question, we
collected a comprehensive dataset (summarized in Table 3) covering
anatomical and physiological responses of each plant species to its
particular phytoplasma infection, supporting a co-evolutionary impact.
Based on these results we are discussing several implications thereof in
the following paragraphs.