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IL “RECOVERY” DA APPLE PROLIFERATION IN MELO È ASSOCIATO ALL' AUMENTO DELLA CONCENTRAZIONE DELLO IONE CALCIO NEL FLOEMA
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Phloem-specific protein expression patterns in apple and grapevine during phytoplasma infection and recovery
No full textRecovery - complete remission of disease symptoms - has been reported in plants affected by phytoplasmas. The physiological basis for this phenomenon is not yet understood, but it seems associated to ultrastructural and biochemical modification of the phloem, the tissue where phytoplasmas live and spread. In this work we compared asymptomatic, phytoplasma-infected and recovered apple and grapevine leaf tissues by means of ultrastructural and gene-expression analyses, focusing on a possible role of specific phloem proteins in the plant defense-related processes. Preliminary results indicate that different occlusion mechanisms could interact in the phloem during phytoplasma symptomatic status and/or recovery
DNA-dependent detection of the grapevine fungal endophytes Aureobasidium pullulans and Epicoccum nigrum
No full textAureobasidium pullulans and Epicoccum nigrum are frequently reported as endophytes of various
crops, including grapevine (Vitis vinifera). Because of their potential role as biological control
agents against grapevine pathogens, we examined the occurrence of A. pullulans and E.
nigrum in two grapevine varieties (Merlot and Prosecco) in Italian vineyards where spontaneous
recovery from phytoplasma disease is recurrent. Species-specific primers for A. pullulans and
two genetically distinct strains of E. nigrum were designed in variable regions of ITS1 and ITS2.
Primer specificity was confirmed by polymerase chain reaction using purified DNA from other
fungal endophytes that are usually encountered during isolation attempts from grapevine tissues
and from several other strains of A. pullulans and E. nigrum isolated from other sources. In order
to determine the occurrence of the two endophytes in grapevine plants, DNA was extracted from
shoots of 44 grapevines collected in six vineyards from different localities of northeast Italy.
Both endophytes were detected and their identity was confirmed by restriction fragment length
polymorphism (RFLP) patterns obtained from reference strains. RFLP analyses confirmed the
presence of two E. nigrum strains belonging to different RFLP groups in grapevine. The molecular
methods described allowed a sensitive, specific, and reliable identification of the two endophytes
in grapevine
Detection of Bois Noir phytoplasma in grapevine roots by reverse transcription-Real Time TaqMan assays
No full textBois noir (BN) is a phytoplasma disease of grapevine spread in
the Mediterranean basin, causing relevant economic losses. BN
phytoplasma diagnosis is currently carried out by detecting the
pathogen DNA sequences in the leaf. Even if reliable and usable
in routine analyses, molecular diagnosis is nevertheless restricted
to the late summer, when BN symptoms become evident. This is
because the above methods are not enough sensitive to carry out
diagnosis in other periods of the year, when symptoms are not evident,
or on other plant organs such as roots. This consideration
suggests that more sensitive and focused detection methods for
BN would be needed. Because of the lack of diagnostic methods
for root tissues, it is not known where the pathogen overwinters
inside the host. We aim at expanding diagnosis effectiveness to
root tissues in BN-infected grapevine, to better understand phytoplasma/
grapevine interactions and to give new insights to BN
epidemiology. Different root samples from healthy, BN-infected
and recovered grapevines, have been collected and RNA was extracted.
As the low concentration of template in the host, we performed
a nested Real-Time PCR using a BN specific TaqMan
probe, following the method already described by Margaria et al.
(Plant Pathol. 58:838-845, 2009). Preliminary analyses showed
positive signal in roots of symptomatic and recovered plants,
whereas no amplification was observed in healthy samples. This
result suggests that BN phytoplasma persists in the root phloem
tissues of recovered individuals. The epidemiological significance
of this finding will be discussed
Interactions between ‘Candidatus Phytoplasma mali’ and the apple endophyte Epicoccum nigrum in Catharanthus roseus plants
No full textPhloem cytological and molecular modifications induced by Bois Noir infection in grapevine plants
No full textPhloem cytochemical modification and gene expression following the recovery of apple plants from apple proliferation disease
No full textRecovery of apple trees from apple proliferation was studied by
combining ultrastructural, cytochemical, and gene expression analyses to
possibly reveal changes linked to recovery-associated resistance. When
compared with either healthy or visibly diseased plants, recovered apple
trees showed abnormal callose and phloem-protein accumulation in their
leaf phloem. Although cytochemical localization detected Ca2+ ions in the
phloem of all the three plant groups, Ca2+ concentration was remarkably
higher in the phloem cytosol of recovered trees. The expression patterns
of five genes encoding callose synthase and of four genes encoding
phloem proteins were analyzed by quantitative real-time reverse transcription-
polymerase chain reaction. In comparison to both healthy and
diseased plants, four of the above nine genes were remarkably upregulated
in recovered trees. As in infected apple trees, phytoplasma
disappear from the crown during winter, but persist in the roots, and it is
suggested that callose synthesis/deposition and phloem-protein plugging
of the sieve tubes would form physical barriers preventing the recolonization
of the crown during the following spring. Since callose deposition
and phloem-protein aggregation are both Ca2+-dependent processes, the
present results suggest that an inward flux of Ca2+ across the phloem
plasma membrane could act as a signal for activating defense reactions
leading to recovery in phytoplasma-infected apple trees
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