GPGV (Grapevine Pinot Gris virus) is a recently-identified grapevine disease which causes significant damages in some white-berry grapevine cultivars. Some authors have argued that Boron deficiency or sub-optimal content of this essential element could trigger the outbreak of symptoms. This hypothesis was supported by experiments carried out in hydroponics, where GPGV symptoms were evident only when grapevines were grown in boron-limited solutions. We hypothesized that a high content of B in the vine could suppress the symptoms and thus negative effects of GPGV in vineyard. We also wanted to check whether toxic effects could occur when exceeding maximum recommended dose of B per hectare by foliar spray.
To test efficacy of B fertilization in increasing B content in vines, an agronomic trial (3 randomized blocks) was set-up in a vineyard grown with “Friulano” cultivar, located in “Villanova” Farm, (Farra d’Isonzo, Northeastern Italy; 45°54’59,5” N; 13°31’51,5” E) in 2018. Treatments were four: 1- control; 2- soil B fertilization (2 times); 3-foliar B fertilization (10 times), 4- foliar (10 times) plus soil (2 times) B fertilization; in all cases B was supplied as a complex with ethanolamine. Before each foliar administration, and after the last one, 5 leaves were sampled from each plot and analysed for their B content as well as for other mineral nutrients (Ca, Cu, Fe, K, Mg, Mn, Na, P and Zn). Soil samples were taken for B quantitation before each fertilization and after second fertilization. Buds were taken in early November (one bud per vine) to be analysed as for the leaves.
Foliar treatments (3 and 4) promptly increased boron content in leaves compared to control; by contrast foliar B concentration increased slightly when this element was added to soil (treatment 2). B concentration in buds taken from soil only fertilization (treatment 2) was not different from control; foliar treatments (3 and 4) were both statistically higher compared to control and not statistically different among them.
No visual reduction of GPGV symptoms were noticed during the season as a consequence of any B fertilization treatment. However, because B reserves in plant are important at sprouting, both visual and B content monitoring will be performed in 2019 growing season.