AVF Proj. ID: 625
Year Funded: 2015
Category: Pest-Disease - Red Blotch
Investigators: David R. Smart

Discerning Mechanisms of GRBaV Virus Disease (Red Blotch) Using Leaf Nutrient Transport and Photosynthesis Analyses

Summary:

In 2015, considerable time was invested in establishing a relationship with the Stanford Synchrotron Radiation Lightsource Facility (SSRL) and working with their beam line scientist to develop a micro X-ray fluorescence method to image micronutrient distributions in grapevine tissue sections.  Images of micronutrient distributions, concentrations and chemical states on a cellular level were not obtained this year due to a malfunction in the beam line equipment, but will be obtained in 2016.  Nutrient levels in leaves in petioles at veraison were measured. Boron (B), an element essential for sugar transport across membranes, was observed to be accumulating in vines that tested positive for GRBaV virus (infected,[RB(+)]). Iron (Fe) levels in RB(+) leaves were observed to be diminished compared to non-infected controls [RB (-)], a situation that may affect the photosynthetic metabolism since Fe is a major catalyst in the production of chlorophyll.  These results suggest the need for SSRL analysis to better understand the changes of these elements, as well as other macro- and micronutrients, on a cellular level between RB(+) and RB(-) vines. Photosynthetic assimilation analysis showed decreased CO2 assimilation in the RB(+) mature leaves closest to fruit clusters yet at the same time starch accumulated in these leaves, suggesting phloem loading (transport) as being disrupted. Sucrose levels in RB(+) mature leaves were higher than RB(-) mature leaves. Sugar (brix) levels in the RB(+) fruit were 14% lower than RB(-) fruit. However in both treatments, sucrose levels between treatments were equally higher in younger RB(-) asymptomatic leaves compared to mature symptomatic leaves. These results, along with the results from Oberholster’s group, suggest that source sink dynamics are being altered by the virus

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