Pear Rootstock Effects on Seasonal Colonization Patterns of Pear Decline Phytoplasma

Abstract

Pear decline (PD) phytoplasma populations were examined over one year in non-symptomatic pear trees with HW620 scions grafted onto three different rootstocks: OH×F87 (PD resistant), OH×F69 (PD susceptible), and Bartlett (PD susceptible). For all three rootstocks, populations were at a maximum during late summer for leaves and shoots, and reached their minimum in mid-winter for shoots and early spring for leaves. In contrast, roots exhibited maximum populations in mid-winter and minimum populations in mid-spring. For all tissue types, PD populations were consistently lowest in trees grafted onto OH×F87 rootstocks, intermediate in those on OH×F69, and highest on Bartlett rootstocks, demonstrating that the type of rootstock significantly impacts PD populations. While OH×F87 rootstocks had the lowest populations, they can still contain relatively high PD populations, particularly during periods with maximum populations. Future research could explore the development of even higher levels of PD resistance in pear rootstocks to reduce PD populations in both the rootstock and scion.

Keywords

• pear decline
• phytoplasma
• dynamics
• seasonal
• phloem