Experimental set-ups
From each tree, two (pear and peach) or four (apple) mature leaves were randomly selected. The mass flow measurements were done in vivo . Thereafter, the leaves were cropped, length and width of the leaf lamina were measured, cross sections were done to analyse the mass flow rate, the middle part of the midrib was fixed in a fixative (see below), and the rest of each leaf was used for phytoplasma titre determination. Leaves for phytohormone measurements were separately collected, immediately frozen in liquid nitrogen and stored at -20 °C until used.