Plant defense mechanisms against pathogens result in differential regulation of various processes of primary and secondary metabolism. Imaging techniques, such as fluorescence imaging and thermography, are very valuable tools providing spatial and temporal information about these processes. In this study, effects of Grapevine leafroll-associated virus 3 (GLRaV-3) on grapevine physiology were analyzed in pot-grown asymptomatic plants of the white cultivar Malvasía de Banyalbufar. The virus triggered changes in the activity of photosynthesis and secondary metabolism. There was a decrease in the photorespiratory intermediates glycine and serine in infected plants, possibly as a defense response against the infection. The content of malate, which plays an important role in plant metabolism, also decreased. These results correlate with the increased non-photochemical quenching found in infected plants. On the other hand, the concentration of flavonols (represented by myricetin, kaempferol and quercetin derivatives) and hydroxycinnamic acids (which include derivatives of caffeic acid) increased following infection by the virus. These compounds could be responsible for the increase in multicolor fluorescence F440 (blue fluorescence) and F520 (green fluorescence) on the leaves, and changes in the fluorescence parameters F440/F680, F440/F740, F520/F680, F520/F740 and F680/F740. The combined analysis of chlorophyll fluorescence kinetics and blue-green fluorescence emitted by phenolics could constitute disease signatures allowing the discrimination between GLRaV-3 infected and non-infected plants at very early stage of infection, prior to the development of symptoms.

Grapevine leafroll disease is one of the most important viral diseases of grapevine (Vitis vinifera) worldwide. Grapevine leafroll-associated virus 3 (GLRaV-3) is the most predominant virus species causing this disease. Therefore, it is important to identify GLRaV-3 effects, especially in plants which do not systematically show visual symptoms. In this study, effects of GLRaV-3 on grapevine physiology were evaluated in asymptomatic plants of Malvasía de Banyalbufar and Cabernet Sauvignon cvs. Absolute virus quantification was performed in order to determine the level of infection of the treatment. The net carbon dioxide (CO 2 ) assimilation (A N ) and electron transport rate (J flux ) were the main parameters affected by the virus. The A N reduction in infected plants was attributed to restrictions in CO 2 diffusion caused by anatomical leaf changes and a reduction of Rubisco activity. Those effects were more evident in Malvasia de Banyalbufar plants. The reduction of A N leads to a decrease in the total oxygen uptake rate by the activity of the cytochrome oxidase pathway, producing slight differences in plant growth. Therefore, even though no symptoms were expressed in the plants, the effects of the virus compromised the plant vital processes, showing the importance of early detection of the virus in order to fight against the infection.Closteroviridae family. In red varieties, symptoms of GLRaV-3 are easily identified, noticeable as dark-red, downward rolling leaves with green veins, but the infection is almost asymptomatic in white varieties. The difficulty in detecting virus can lead to rapid spread of virus-infected material through propagation. Diagnostic methods for the detection of grapevine viruses have been developed over the last few years. These methods include: biological indexing (Habili et al., 1992), enzyme-linked immunosorbent assay (ELISA) (Rowhani, 1992;Frosline et al., 1996;Rowhani et al., 1997) and nucleic acid-based methods, mainly PCR methods (Minafra et al.Grapevine leafroll-associated virus 3 effects on plant physiology R. Montero et al.

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