Grapevine leafroll disease: an econphysiological perspective

Matthew Magnus Halldorson

Grapevine leafroll associated viruses, and their accompanying disease symptoms contribute to losses in fruit quality both in the State of Washington and worldwide. While grapevine leafroll disease alone can compromise vine productivity, it is commonly believed that the combination of viral diseases and abiotic factors such as cold and drought exacerbate losses. Visually, leafroll disease symptoms appear similar to those associated with an imbalance in source/sink relations and its associated feedback inhibition of photosynthesis. If it is indeed the case that the disease symptoms result in a down-regulation of photosynthesis, this would presumably result in a reduction in stomatal conductance, effectively lowering transpiration and increasing drought tolerance of infected vines. Furthermore, if virus infection causes an impasse in sugar translocation, passive phloem leakage could act to lower the plant's overall solute potential and increase cold-hardiness. In order to test these hypotheses as well as the feedback inhibition of photosynthesis, 12 pairs (healthy and infected) of own-rooted Merlot vines grown North of Prosser, Washington were observed for gas exchange, chlorophyll content, water potential, cold-hardiness, and non-structural carbohydrates. Foliar non-structural carbohydrate content was found to be significantly higher in infected vines both before and after veraison, with significantly more starch being accumulated in infected vines occurring earliest in the season, followed by soluble sugars. Gas exchange was also found to be significantly lower in infected vines late in the growing season after carbohydrate accumulation was witnessed. Further, strong negative correlations were seen between photosynthesis and sugar accumulation. Though both transpiration and stomatal conductance were found to be lower in infected vines after veraison, this did not effectively correlate into significantly higher water potential values. Additionally, no differences were found regarding the cold-hardiness was not found to be significantly different between healthy and infected vines. These findings however, provide evidence that infected vines are no more susceptible to drought or winter damage than their healthy counterparts.

Grapevine leafroll disease: an econphysiological perspective

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