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Two phytoplasmas closely related to the X-disease group were associated with China-tree (Melia azedarach L.) and garlic (Allium sativum L.) decline diseases in Argentina. The present work was aimed at studying their phylogenetic relationship based on molecular characterization of the 16S ribosomal DNA sequences. Phytoplasma DNAs were obtained from naturally infected China-tree and garlic plants from different geographical isolates. The results from analysis of restriction fragment length polymorphisms and nucleotide sequences of the 16S rDNA showed the affiliation of China-tree and garlic decline phytoplasmas to the 16SrIII (X-disease group), subgroups B and J, respectively. Both organisms had high sequence similarities in the 16SrDNA nucleotide sequence with the Chayote witchesÕ broom phytoplasma from Brazil. The phylogenetic tree, constructed by parsimony analysis, grouped the Garlic decline, China-tree decline, Chayote witchesÕ broom and Clover yellow edge phytoplasmas into a cluster separated from the other phytoplasmas of the X-disease group.U. S.

Garlic plants (Allium sativum L.) showing symptoms of decline, absence of cloves, leaf yellowing (in ‘Rosado Paraguayo’ and ‘Colorado’ type) and reddening (in ‘Blanco’ type), have been observed in certain areas around the city of Córdoba, Argentina. This syndrome was termed ‘tristeza del ajo’ (garlic decline) by growers. Symptoms appear during the second half of the growth cycle. Affected plants die, and have spongy bulbs with undeveloped cloves. When symptoms appear close to harvest time, plants show only a colour change in leaves, but bulbs appear normal. Plants with symptoms showed abundant phytoplasma cells when observed under electron microscopy, and strongly reacted with an antiserum raised against the phytoplasma associated with ‘China‐tree (Melia azedarach L.) decline’. Using universal primers to phytoplasma, a DNA fragment from leaf and clove extracts of plants expressing symptoms was amplified by PCR. The PCR amplified product was digested with the restriction enzyme Alu I, and the generated restriction pattern was analysed in polyacrylamide gels. This allowed the location of the pathogen within Group ill of the classification proposed by Ahrens and Seemüller (1992). These results confirm the association between the symptomatology described as ‘tristeza del ajo’ and a phytoplasma. supporting our first report from 1992. on the presence of this prokaryote in garlic. Zusammenfassung Mit den Symptomen der Kümmerkrankheit “Tristeza del ajo” bei Knoblauch (Allium sativum L.) ist ein Phytoplasma assoziiert In der Nähe der argentinischen Stadt Cordoba wurden Knoblauchpfianzen (Allium sativum L.) mit folgenden Symptomen gefunden: Kümmern. fehlende Zehenbildung, Blattvergilbung (bei den Typen “Rosado Paraguay” und “Colorado”) und Rötung (beim Typ “Blanco”). Die Anbauer bezeichneten dieses Syndrom als “Tristeza del ajo” (“Kümmerkrankheit des Knoblauchs”). Die Symptome treten in der zweiten Hälfte des Wachstumszyklus auf. Betroffene Pflanzen sterben ab und bilden nur schwammartige Zwiebeln. in denen sich keine Zehen finden. Treten die Symptome erst kurz vor der Ernte auf, so zeigen die Pflanzen nur eine Verfärbung der Blätter, und ihre Zwiebeln erscheinen normal. Elektronenmikroskopische Untersuchungen ergaben. Daß Symptome aufweisende Pflanzen zahlreiche Phytoplasmazellen enthielten. zudem reagierten sie stark mit einem Antiserum gegen das mit der Kümmerkrankheit des Zedrachbaums (Melia azedarach L.) assoziierte Phytoplasma. Unter Verwendung universeller Primer für Phytoplasmen wurde ein DNA‐Fragment aus Blatt‐ und Zehenextrakten Symptome aufweisender Pflanzen mit Hilfe der PCR‐Technik amplifiziert. Das PCR‐amplifizierte Produkt wurde mit dem Restriktionsenzym Alu I gesehnitten. und das entstandene Restriktionsmusler wurde in Polyacrylamidgelen analysiert. Dadurch wurde es möglich, das Pathogen in Gruppe III der von Ahrens und Seemüller (1992) vorgeschlagenen Klassifikationsschemas einzustufen. Diese Ergebnisse bestätigen die Verbindung zwischen den als “Tristeza del ajo” beschriebenen Symptomen und der ...

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Fluctuations in Prunus necrotic ringspot virus (PNRSV) concentration were researched in single plants of six peach (Prunus persicae) cultivars—Kurakata, Red Haven, Nectar Red, Start Delicious, Meadowlark, and Loadel—by double antibody sandwich-enzyme-linked immunosorbent assay (DAS-ELISA) of dormant buds (May, June), flowers (September), new sprouts (November), and mature leaves (January) (Southern Hemisphere). The optimum extract dilution (sample weight per buffer volume) to detect the virus was also quantified. The average absorbance patterns of the six cultivars show a steady increase in virus concentration, ranging from A 405nm 0.61 in May to A 405nm 0.86 in July for dormant buds, to A 405nm 1.22 in September in flowers, to 1.53 in November in new sprouts, where the highest concentration was found. Virus concentrations in mature leaves drop to values similar to those of noninfected plants in January ( A405nm 0.12). The yearly average (six noninfected peach trees) ranged from A405nm 0.04 to A405nm 0.08. This drop coincides with an increase in summer temperature and attenuates foliation symptoms caused by PNRSV. Analysis of dormants buds, flowers, or new sprouts with 5-cm-long leaves was reliable to differentiate infected from noninfected plants. Cluster analysis of absorbance profiles for single plants of cvs. Loadel and Meadowlark, however, showed a comparatively low profile, with a drop at flowering time (A405nm 0.20 in September) close to the average of healthy controls. The difference between infected and healthy plants did not become apparent in all cultivars from the analysis of plants at a given phenological stage, for example by the analysis of flower only, the material most preferred to diagnose the virus. Therefore, plants should be analyzed during flowering and sprouting or flowering and dormancy (dormant buds).