3.7.49
NATURAL INFECTION OF WILD AND CULTIVATED PEARS IN GREECE WITH PEACH LATENT MOSAIC VIROID AND POME FRUIT VIROIDS

PE KYRIAKOPOULOU, A HADIDI, K DOUGDOUG and L GIUNCHEDI

Fruit Laboratory, ARS USDA, Beltsville, MD 20705, USA

Background and objecdves
For years it was presumed that peach latent mosaic viroid (PLMVD) naturally infects peach only. Recently, however, it has been demonstrated that plum, cherry and apricot are natural hosts of PLMVD [1,2]. During the last 3 years we have investigated possible natural infection of wild and cultivated pears (Pyrus amygdaliformis and P. communis, respectively) in Greece with PLMVD. Natural infection of Greek pears with apple scar skin viroid (ASSVD) and pear blister canker viroid (PBCVD) was also investigated. ASSVD infection has been described in Asian but not European pears. PBCVD is common in European pears.

Materials and methods
We have utilized recombinant DNA, polymerase chain reaction (PCR) and nucleotide sequencing technologies in this investigation.

Results and conclusions
Hybridization experiments of pear total nucleic acids from leaf, fruit or bark tissue with DIG-1 1 -labeled PLMVD, ASSVD, or PBCVD CRNA probes revealed PLMVD, ASSVD and PBCVD related sequences in wild and cultivated pears. PBCVD was most common, followed by PLMVd, then ASSVD. To ascertain that full length PLWD and ASSVD molecules were present in pear nucleic acid extracts and that the hybridization of ASSVD and PLWD probes were not only due to the short nucleotide segments of ASSVD and PLWD in the recombinant PBCVD, we have used RT-PCR to amplify PLMVD DNA and ASSVD DNA from pear nucleic acids. When PLMVD primers were used for RT-PCR, amplified DNA of the expected size (336-337 bp) was obtained. Similarly, when ASSVD primers were used for RT-PCR, amplified DNA of the expected size (330 bp) was also detected. Products of the expected size were also obtained in RT-PCR assays using PLMVD primers with nucleic acid extracts of an Italian pear cultivar from Bologna. Cloning and sequencing of DNA that was RT-PCR amplified with PLMVD primers revealed typical PLMVD nucleotde sequences from naturally infected Greek and Italian pears with a chain length of 338 nucleotides. Therefore: i) the host range of PLMVD is not restricted to stone fruits. Pear, which is a member of the pome fruits, is also a host; ii) European pears, as with Asian pears, are natural hosts of ASSVD; iii) viroids have evolved in wild plant species.

References
1. Giunchedi L, Hadidi A, Poggi-Poilini C, Bissani R, Mordent GL, Lugaresi C, 1997. Rivista di Frutficolturae di Ortofloricultura 59,92-94.
2. Hadidi A, Giunchedi L, Shamioul AM, Poggi-Poilini C, Amer AM, 1997. Plant Disease 81,154-158.