Condition of the Phloem and the Persistence of Mycoplasmalike Organisms Associated with Apple Proliferation and Pear Decline

Persistence of the European Stone Fruit Yellows Phytoplasma in Aerial Parts of Prunus Taxa During the Dormant Season

“…However, he observed during the winter in cherry phloem, adjacent to the cambial zone, a layer of turgid sieve tubes which were without definitive callose and smaller than sieve tubes active in SEEMOLLER, STOLZ und KJSON summer. These so-called winter sieve tubes were anatomically similar to those described for apple and pear by Schaper and Seemuller (1982) but occurred much more frequently. It is conceivable that phytoplasmas can overwinter in such kind of phloem.…”

“…In this way, the sieve tubes become an unsuitable environment for the survival of the phytoplasmas. Although Schaper and Seemuller (1982) observed a few small turgid sieve tubes adjacent to the cambial zone in both apple and pear, these sieve tubes, for still unknown reasons, play no role in the persistence and transmissibility of the pathogens.…”

“…However, since Schneider (1945a) obviously did not observe 'winter sieve tubes' in peach, another possibility may exist. As phytoplasmas induce phloem necrosis in many plants, a more or less pronounced replacement phloem is often formed in infected plants including peach (Schneider, 1945b), pear (Batjer and Schneider, 1960), and apple (Schaper and Seemuller, 1982). In the replacement phloem of witches'brooms of apple proliferation-infected apple trees, phloem layers with functional sieve tubes were observed throughout the winter.…”

“…Both the AP and PD phytoplasmas are known to be unable to persist in the aerial parts (stem) of the trees during winter because the sieve tubes, on which the phytoplasmas seem to depend in most plants, degenerate at the end of the growing season. In contrast, the AP and PD phytoplasmas do survive in the roots where functional sieve tubes are present throughout the year (Schaper and Seemuller, 1982;Seemiiller et al. 1984).…”

PM 3/84 (1) Inspection of places of production for ‘Candidatus Phytoplasma pyri’

“…Phytoplasmas are detected in phloem tissues in shoots from midsummer to the end of sap flow. Detection on roots is possible throughout the year, although uneven distribution also applies here (Schaper & Seem€ uller, 1982;Seem€ uller et al, 1984). This should be considered when looking for symptoms or taking samples.…”