J. Fránová, K. Petrzik
Strawberry plants (Fragaria × ananassa Duch.) cv. Senga Sengana and Fratina with vigorous growth and without distinct disease symptoms (regular shape and colour of leaves, high quantity of normal flowers and runners) did not produce any fruit or very severely deformed fruits. No positive results were obtained by mechanical inoculation of herbaceous hosts and ELISA. Electron microscopy of negatively stained partially purified preparations showed only a few isometric virus–like particles and no pathogens or tissue abnormalities were observed in ultrathin sections. After leaf grafting Fragaria vesca indicator clones revealed symptoms resembling the presence of strawberry mottle virus. Three periwinkle recipient plants that had been parasitised by Cuscuta spp. bridged from one examined strawberry plant developed symptoms of increased number of flowers of smaller size but of regular shape, increased number of axillary shoots, yellowing, dwarfing and produced abnormally small, sterile seeds, if any. Strawberry plants and periwinkles were tested for the presence of phytoplasmas. Nested PCR procedures were employed with different sets of primers to amplify phytoplasma 16SrDNA plus spacer region. RFLP analyses of phytoplasma 16S rDNAs (R16F2/R16R2 nested PCR products) after digestion with endonucleases MseI, HhaI, RsaI and TaqI revealed profiles typical for phytoplasmas belonging to aster yellows group, 16Sr I-B and 16SrI-C subgroups. Mixed infection was observed in all naturally infected strawberries and also graft inoculated F. vesca clones. RFLP analyses of DNA sequences from periwinkles revealed the presence of single phytoplasma infections of 16SrI-B subgroup in one plant and of 16Sr I-C subgroup in the second plant. The RFLP profile from the third periwinkle plant was very similar to those of 16Sr I-C phytoplasmas; however, the fourth band, at the size position 208 bp was missing. DNA sequencing confirmed the presence of phytoplasma 16SrI-C subgroup in naturally infected strawberry 'Senga Sengana', graft inoculated F. vesca 'Alpine' and in one periwinkle plant. We conclude that mixed infection of phytoplasmas belonging to the 16SrI-B and 16SrI-C subgroups in strawberries may be involved in this disease.
Fránová, J. and Petrzik, K. (2008). STRAWBERRY STERILITY – WHAT IS THE CAUSAL AGENT(S)?. Acta Hortic. 780, 27-34
DOI: 10.17660/ActaHortic.2008.780.3
strawberry sterility, biological experiments, viruses, phytoplasmas, PCR, RFLP, sequencing