Submitted to: Acta Horticulturae
Publication Type: Proceedings
Publication Acceptance Date: 9/14/1998
Publication Date: N/A
Interpretive Summary: Stone and pome fruit phytoplasmas ae the causal agents of diseases of quarantine importance to the U.S. Among these diseases are: apple proliferation, plum leptonecrosis, and apricot chlorotic leaf roll which do not occur in the U.S.; pear decline and X-disease of stone fruits which are common in the U.S. and other countries. These phytoplasmas were detected from their respective hosts using universal primers in polymerase chain reaction (PCR) assays. These assays were sensitive enough to detect X-disease phytoplasma in dormant cherry and peach buds. These findings may be of significant importance for the detection of phytoplasma in stone fruits during the international movement of germplasm. We have also developed PCR assays which differentiate plum leptonecrosis phytoplasma from the closely related apple proliferation or pear decline phytoplasma. A precise diagnosis of the causal agent of plum leptonecrosis disease is useful and important for epidemiological studies of the disease.
Technical Abstract: Various oligonucleotide primers, derived from the 16S rRNA were used to detect phytoplasmas associated with apple proliferation (AP), plum leptonecrosis (PLN), pear decline (PD), apricot chlorotic leaf roll (ACLR), and X-disease. Primers AP3-AP5 were successfully utilized for amplification of AP, PLN, and PD DNA fragments from fruit trees and of AP and PLN DNA fragments from infected periwinkle. AP and PLN PCR products were cloned into a plasmid vector and then sequenced. An attempt was made to design PLN specific primers based on a few nucleotides that are different between PLN and AP. These primers in PCR assays gave a higher yield of products from PLN infected tissue than from AP and PD infected tissue. The primers were more specific if used in nested PCR with PCR products obtained with AP-group specific AP3-AP5 primers. The universal primers R16F2-R16R2 were also used for PCR detection of several phytoplasmas, including AP, ACLR and X-Disease. Therefore, the primers can be used in PCR assays for the reliable and sensitive diagnosis of phytoplasmas affecting pome and stone fruits. PCR assays were also sensitive enough to amplify phytoplasma DNA fragments from dormant infected Prunus material. Thus, PCR assays may be used for phytoplasma detection in Prunus germplasm in quarantine and certification programs.