Over the past twenty years, many vineyards across the world have shown signs of deterioration, with vine yields and longevity declining and vine mortality significantly increasing. According to researchers, dieback due to vine wood diseases such as esca – a disease caused by parasitic fungi for which there is no curative treatment – are responsible for the loss of five percent of vineyard surface each year.
“The world is witnessing a sharp increase in perennial plant dieback,” wrote the study authors. “The hypothesized cause is that environmental stresses such as drought are interacting with pathogens fueling plant decline. Global vitculture has seen similar decreases in fruit yield and vine longevity.”
Until recently, a prominent hypothesis explaining the increase in vine dieback has relied upon a postulated synergy between environmental factors such as the increased frequency and intensity of droughts and diseases like esca. However, a new study led by the National Research Institute for Agriculture, Food, and Environment (INRAE) has found that droughts are actually inhibiting esca disease.
“In sharp contrast to this theory, our study demonstrates that drought completely suppresses esca leaf symptoms, and although esca and drought both alter plant water transport and carbon balance, they do so in completely distinct ways,” the researchers explained.
Since esca is affecting vines over seven years old, it can usually be observed only in outdoors plots. However, by using a method of transplanting vines into pots that was similar to techniques used to grow bonsai trees, the scientists managed to transplant dozens of 30-year-old Sauvignon Blanc vines from the INRAE Grande Ferrade experimental estate near Bordeaux, and monitored the appearance of esca symptoms in a controlled environment. Half of the vines were placed under drought conditions.
The study revealed that no vines under moderate to severe drought conditions exhibited any esca symptoms. The scientists suggested several possible explanations for this surprising result. Water deficits caused by drought could inhibit the activity of the parasitic fungi causing esca or could affect the plant’s defense responses. Another hypothesis was that reduction in water transport in the plant could also suppress the transport of toxic chemicals produced by the fungi.
Further research is needed to clarify the role of climate on esca expression on a national and international scale, and to accurately predict the appearance of esca symptoms by monitoring drought indices.
The study is published in the journal Proceedings of the National Academy of Sciences.