High level of resistance of sweet cherry (Prunus avium L.) towards European stone fruit yellows phytoplasmas

摘要

Thirteen sweet cherry cultivars were bud-inoculated with European stone fruit yellows (ESFY) phytoplasmas and observed for symptom expression under field conditions. Only one out of 375 inoculated trees developed ESFY-typical symptoms of early bud break. All other trees showed no evident symptoms. The symptomatic tree, cv. Bing, was positive with DAPI staining and pathogen-specific polymerase chain reaction (PCR). In a complementary experiment, ESFY-phytoplasmas were separately bud-inoculated on Bing and on the highly susceptible Prunus persica cv. Higama. After 4 years, buds from these trees were used to retroinoculate indicator plants of Higama and P. armeniaca cv. Luizet. All of the retroinoculations from Higama were successful but none of theretroinoculations from Bing became infected, as confirmed by PCR. To study the resistance mechanism, Bing was double grafted together with the indicator Higama onto a compatible rootstock. After ESFY phytoplasma-inoculation on Higama, all of the 38 Higama scions but only 3 of the double grafted Bing scions became infected. After inoculation on Bing, all of the corresponding Higama scions became infected but only one of the 7 transmitting Bing scions remained diseased 5 years after inoculation. Thus, itis the multiplication of ESFY phytoplasmas rather than the translocation which seems to be limited in P. avium. These results indicate that sweet cherry is highly resistant to ESFY phytoplasmas.