Pseudomonas viridiflava, a Multi Host Plant Pathogen with Significant Genetic Variation at the Molecular Level

The pectinolytic species Pseudomonas viridiflava has a wide host range among plants, causing foliar and stem necrotic lesions and basal stem and root rots. However, little is known about the molecular evolution of this species. In this study we investigated the intraspecies genetic variation of P. viridiflava amongst local (Cretan), as well as international isolates of the pathogen. The genetic and phenotypic variability were investigated by molecular fingerprinting (rep-PCR) and partial sequencing of three housekeeping genes (gyrB, rpoD and rpoB), and by biochemical and pathogenicity profiling. The biochemical tests and pathogenicity profiling did not reveal any variability among the isolates studied. However, the molecular fingerprinting patterns and housekeeping gene sequences clearly differentiated them. In a broader phylogenetic comparison of housekeeping gene sequences deposited in GenBank, significant genetic variability at the molecular level was found between isolates of P. viridiflava originated from different host species as well as among isolates from the same host. Our results provide a basis for more comprehensive understanding of the biology, sources and shifts in genetic diversity and evolution of P. viridiflava populations and should support the development of molecular identification tools and epidemiological studies in diseases caused by this species

The 'birch-leafroll disease' emerging in forests and urban parks in Fennoscandia - Viral agents associated with the disease

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Investigation on the apple proliferation epidemics in the orchards of the Pelion Mountain and preliminary observations on possible phytoplasma vectors

The apple producing region in the Pelion Mountain (Magnesia prefecture, Thessaly, Greece) is suffering for more than 10 years from the apple proliferation disease. The orchards are basically planted with cv 'Starking Delicious', are grafted on seedling rootstocks and are older than 40 years. The presence of the 'Candidams Phytoplasma mali' was proven by PCR/RFLP analyses as well as by sequencing. 'Ca. P. pyri' was also detected in at least three different orchards. First attempts to identify the vectors were carried out by monitoring the insect populations in 8 different orchards, one species of psyllids morphologically identified as Cacopsylla pulchella (Low) was the most present insect in the orchards all along the two-month monitoring (May/June). Cacopsylla mali (Schmidberger) was also present in the orchards but in lower numbers. The monitoring is continued and still in progress

First report of Candidatus phytoplasma mali in Greece and correlation with small apple fruit disorder occurring in the orchards of the pelion mountain

The apple producing area of the Pelion Mountain suffers the last six years from the extensive phenomenon of small fruiting. Small fruit may appear in few or even all trees of the orchards as well as on few or several branches of each tree. Recovery phenomena and reappearance of the symptoms were observed. Malus xdomestica 'Starking Delicious', widely cultivated at Pelion Mountain, showed high susceptibility. Preliminary studies on the aetiology of this phenomenon were focused to physiological abnormalities in small fruits and to pathogen detection. In small fruits, a high concentration of Mn is observed. The basic colour is not modified, but anthocyanids in the phloem are reduced. Soluble solids and dry mass is decreased, but no difference in pH and acidity is measured. Small apples also show inability in reaching maturation, as they are harder and remain on the tree for many weeks after harvest. Injections with oxytetracycline in a small number of trees were carried out; in the next year a remission of the symptoms in 60% of cases was observed. In September 2005, PCR diagnostic tests for Candidatus Phytoplasma mali in symptomatic trees were performed revealing high presence of the pathogen in the region; out of the 131 trees tested, 43 were positive. The high detection rate of Candidatus Phytoplasma mali in symptomatic trees reveals the high correlation of the presence of the pathogen with small fruit disorder