Grapevine Thermotherapy Effects

Among woody plants, grapevine, apple and peach are the most frequent targets of sanitation protocols because their health status is strictly ______

Even if thermotherapy represents the preferred method for the host, grapevine viruses can also be eliminated with ______ and tissue culture

apple viruses respond to ______ as well

With regard to virus, thermotherapy was successfully applied against viruses belonging to 13 families and an unassigned ______

Tissue culture, usually adopted to regenerate plantlets in biotechnological breeding programs, represents the less used tool for eliminate viruses from ______

Thermotherapy treatment involves keeping plants or plant parts at temperatures between 35°C and ______°C for an appropriate period

The most frequent thermal cycles reported in trials are between 35°C and ______°C

Thermotherapy was successfully applied against viruses in 13 families and an ______ genus

The paper was received on ______ and accepted on 04-02-13

Thermotherapy was conducted on plants infected by Cassava mosaic disease and the close relationship between temperature and VIGS was confirmed. Qu et al. (2005) considered plants of N. benthamiana infected by Potato virus X exposed to different thermal regimes (up to 33°C) with particular attention to the involvement of RNA-dependent RNA polymerase (RdRp), which is sensitive to temperature changes and thus induces the silencing complex, thereby highlighting its role. Wang et al. (2008) conducted combined thermotherapy (38°C) and cryotherapy treatments associated with the removal of meristem tips on raspberry plants infected by Raspberry dwarf virus. From their results, the authors noted the close relationship between temperature and RNA silencing which seems to act as a means to increase the degradation of virus RNA.

The development of research in the field of chemotherapy has not been as lively as the work conducted on thermotherapy, but valuable contributions have been provided by the most extensive investigations of anti-viral chemotherapy performed in clinical medicine. In this regard, the discovery of ribavirin (Sidwell et al., 1972; Huffman et al., 1973) represented a defining moment in the research, marking a different route of investigation in the study of new chemical synthesis analogues of nucleoside or precursors of RNA bases. In fact, knowledge of the complex interactions that develop between virus and host cell provides a guide for selecting the potentially most suitable treatment. To date, more than 40 antiviral molecules, synthesized in this way, are available on the market for clinical application. Keeping in mind the relevant differences between animal and plant hosts, the potential similarities between metabolic pathways present in both have been the starting point for experimentation on phytoviruses, making possible to highlight the effectiveness of these antiviral drugs in the botanical field. However, in plant virology, the fact that less resources are available and that there has been a delay in knowledge of the molecular characteristics of many phytoviruses, means that fewer results than in medicine are available.

Chemotherapy applications ______ plants were more frequently investigated than woody plants, with 66.0% and 34.0% respectively of published trials in 1991-2010 (Table 2). Potato (18.9%), orchid and tobacco (9.4%) were subjected to many treatments, while grapevine sanitation represented the main treated host among woody plants (11.3%) as well as apple and plum (7.5%). Chemotherapy, mainly with well-known pro-drugs such as ribavirin, was successfully performed against viruses belonging to 9 families and an unassigned genus (Table 2). Synthetic nucleoside such as tiazofurin, selenazofurin (2-pD-ribofuranosylselenazole-4-carboxamide) and benzamide riboside (3-(l-deoxy-pD-ribofuranosyl)benzamide, and non-nucleosides such as micophenolic acid [6-(4-hydroxy-6-methoxy-7-methyl-3-oxo-l,3-dihydroisobenzofuran-5-yl)-4-methyl-hex-4-enoic acid] were tested against Cucumber mosaic cucumovirus (CMV) and Grapevine leafroll-associated virus 3 (GLRaV-3) (Panattoni et al., 2005, 2007a). Interesting results were obtained using dihydroxypropyladenine [(RS)-9-(2,3-dihydroxypropyl) adenine] in combination with ribavirin and resulted in the elimination of Grapevine vitivirus A (Panattoni et al., 2007b). Surprising positive results were achieved by supplying oseltamivir to in vitro Nicotiana tabacum explants infected by CMV and V. vinifera explants infected by GLRaV-3; high rates of sanitation in both combinations were noted (D’Annaet al., 2006; Panattoni et al., 2006; Guta et al., 2010). Moreover, replication of Tobacco mosaic virus (TMV) was inhibited by bitriazolyl compounds (Xia et al., 2006), tylophorine B (Xi et al., 2006), phenanthrene-based tylophorine derivatives (Wang et al., 2010a), derivatives of thiadiazole-acetamide (Zhao et al., 2006), cyanoacrylate derivatives (Chen et al., 2008), and racemic phenanthroindolizidine alkaloids or pure alkaloids (Wang et al., 2010b): no sanitized plants were reported for these novel compounds.

Keeping in mind the relevant differences between animal and plant hosts, the potential similarities between metabolic pathways present in both have been the starting point for experimentation on phytoviruses, making possible to highlight the effectiveness of these antiviral drugs in the botanical field. However, in plant virology, the fact that less resources are available and that there has been a delay in knowledge of the molecular characteristics of many phytoviruses, means that fewer results than in medicine are available.

Thermotherapy has been more effective against ______ viruses localized in differentiated tissue, whereas meristem culture is suitable for phloematic viruses

The Virus-Induced Gene Silencing (VIGS) is characterized by adaptability and mobility at the ______ level

Studies have shown a correlation between VIGS and the thermal regimes to which a plant is exposed, with increased gene silencing at higher temperatures and a decrease in susceptibility to virus infections (Szittya et al., 2003; Qu et al., 2005). Investigations on the mechanisms that determine the influence of temperature on antiviral silencing, such as the study by Chellapan et al. (2005), have demonstrated the importance of understanding the ______ gene silencing mechanisms for effectively eliminating viral infections in plants

The study of infected plants has revealed that the VIGS process is effective at low temperatures, but increased heat stress enhances the host defense system's capacity, creating a ______ to infection

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