Gene expression analysis and cytochemical investigations in ‘Candidatus Phytoplasma mali’-resistant and -susceptible Malus genotypes grown in vitro

A gene expression study was carried out in ‘Candidatus Phytoplasma mali’-resistant and -susceptible apple genotypes infected with ‘Ca. P. mali’. Genes involved in the general response against stress and pathogens were found to be differentially expressed in the ‘Ca. P. mali’ resistant wild genotype Malus sieboldii. Furthermore, cellular modifications and ultrastructural features were investigated through cytochemical analysis performed on healthy and ‘Ca. P. mali’-infected in vitro plants of Malus sieboldii and the ‘Ca. P. mali’-susceptible Malus x domestica cv. Golden Delicious. Preliminary results showed that while the cellular organisation in the susceptible genotype was deeply affected by the presence of ’Ca. P. mali’ only few localised structural modifications were observed in the resistant genotype